John Wolff's Web Museum

Rebuilding the Model J Comptometer


Comptometer J, 1926-39.
Comptometer J, 1926-39.


These notes give a detailed step-by-step procedure for a complete disassembly, reassembly, and adjustment of the Felt & Tarrant Model J Comptometer (including the Sterling-curency machines). The procedure can also be used for the earlier Model H with only minor changes. A separate procedure is provided for rebuilding the later Model 3D11. Readers with a Model M should adapt the relevant sections from each procedure.

The notes have been prepared and refined during the rebuilding of a significant number of Felt & Tarrant machines of various types. There are no particular difficulties in rebuilding a Comptometer, and there is no requirement for workshop facilities or special tools. However it does require patience, care, and attention to detail. The procedure following works well for me, but comes with no guarantees. No responsibility will be taken for any consequences arising from the use of these notes by others.

The notes are intended to be read in conjunction with the Technical Description of the Model J Comptometer, and with the more general information in the Notes on overhauling a mechanical calculator. The Technical Description explains the construction and operation of the Model J mechanism and illustrates all of the major components and assemblies, while the Notes on Overhaul describe more general techniques for disassembly, cleaning, and rebuilding. Please study this material carefully before commencing your overhaul, and refer back frequently for the illustrations as you proceed.

I would be happy to receive feedback, comments, or suggestions via the enquiry form.


Disassembly does not require any special tools, although a good pair of bent-nose tweezers or fine pliers will be found useful. Except where advised otherwise, it is strongly recomended that you keep the parts in column order during disassembly and cleaning. The extra time taken will be saved many times over by avoiding trouble in reassembly and adjustment. Accumulators, for example, were selected in the factory according to the angular (mis-)alignment between the pinion and the accumulator gear, and may cause significant problems if paired incorrectly. Keeping columns together is especially important in non-decimal machines, where many similar components have small differences but big incompatibilities.

A Comptometer can be disassembled to frame level in about 3 to 4 hours if no problems are encountered. A thoroughly gummed cross-shaft can take 4 hours on its own.

Please review the material in the Notes on overhauling a mechanical calculator, and proceed as follows:

  1. Preliminaries Model J frame plate outline drawing
  2. Print a copy of these notes, and tick off each step as it is completed.
  3. Print the frame plate outline drawing (PDF file, 286kb) to show the location of the 28 cross-shafts and wires which support the mechanism . The numbering 1 to 33 in this drawing is the same as in the 3D11 rebuilding procedure. Wires 10, 15, 16, 19, and 30 are not used in the Model J.
  4. Prepare sets of numbered bags or containers to receive groups of parts in column order, and to store the cleaned parts. Column 1 is on the right. Prepare containers labelled A to K to receive the frame tie rods, spacers, and shims.
  5. Remove the clearing handle.
  6. Remove the two screws in the numeral wheel cover. Pull the cover forward and remove.
  7. Lift the machine off the bench, turn it over, and set it down carefully on its keys on a soft towel. Do not roll it over, as this can break the keytops. Remove the four countersunk screws near the corners of the base.
  8. Lift the base and sides away from the keyplate and the mechanism. The mechanism is a close fit inside the case, and will probably be stuck to the internal lining in several places. Stand the machine on its back while loosening the case to avoid damage to the keys, then set it down on the keys and lift off the base and sides together.
  9. Set the machine back on its internal feet.

  10. The rock frame.
  11. Replace the clearing handle and clear the machine.
  12. Withdraw the numeral wheel pivot wire 9. Remove the numeral wheels and store them in column order in the numbered containers.
  13. Release the clip at the right-hand end of the rock frame toggle pivot wire 4. Pull the rock frame forward and withdraw the wire to the right.
  14. Press any key to release the detaining toggle, or press rearward on wire 28. Lift the front of the machine and remove the support wire 3 which passes through the slots in the rock frame actuating links. Pull the rock frame forward and disengage the forked actuating links from the pins on the rock frame plates. Place a suitable block under the front of the machine so as not to damage the links when putting the machine back down.
  15. Withdraw wire 7 one column to the left and remove the first intermediate gear. Insert a short temporary pin (eg the shank of a 7/64" drill) at the right-hand end to support the rock frame as wire 7 is withdrawn, then remove the remaining intermediate gears. Leave wire 7 in place to support the rock frame at the left-hand side. (If you have the facilities, it is convenient to make up a couple of short temporary pins of 7/64" (0.108") diameter to support the rock frame during removal and reinstallation).
  16. In Sterling machines, there should be a special accumulator latch for the 10/- column pivoted on wire 7 in the first pounds column. If present, detach its spring and lift out.
  17. Check that all the formed spacers on tie rod E are lifted hard up against the spring support wire 8. Loosen the left-hand screw in tie rod E and adjust if necessary.
  18. Locate the linoleum guards (standing vertically from tie rod A) and pull them forward and clear of the rock frame. Loosen the left-hand screw in the tie rod if necessary.
  19. Rock frame position for insertion or removal Support the rock frame with one hand and remove wire 7 and/or the temporary pins. Hold the rock frame at each end, lift it straight up as far as it will go, and pull it forward to clear the duplex levers. Rotate the top forward until the two locating flanges (top centre) are clear of the main frame plates, then push it across to the right. The movement is only about 1mm, just enough for the toggle levers to clear the toggle link rivets. Sit the leftmost escapement lever over the toggle link mounting point, as illustrated, then swing the top of the rock frame forward so that it passes under the top spacer bar E. Lift out carefully to avoid catching on the carry levers, and set aside. Although it may seem impossible at first, the rock frame can actually be removed and replaced quite easily after a bit of practice (and you'll get plenty of practice by the time you've finished). It is never necessary to use force, to remove the tie rod, or to modify any part of the machine.
  20. In Sterling machines, unhook spring 3.8x27x0.32 from the tab on tie rod A and lift out the interlock lever from the bottom of the 10/- column.

  21. The accumulators.
  22. Loosen the screw at the left-hand side of the top front spacer bar E. Push the front lip of the spacers down just enough to free the carry lever spring retainer wire 8. Withdraw the wire and release the springs.
  23. Note the location of the accumulator backstops and their torsion springs on wire 6 at the right of each column. Support the front of the machine a few inches off the bench and carefully unhook the bottoms of the springs where they pass over the frame plate.
  24. Withdraw the backstop wire 6 gradually to the left and remove the backstop spring, the backstop, the carry lever assembly, and the accumulator latch lifter (between the arms of the carry lever). Store the parts in column order.
  25. Withdraw the accumulator wire 5 gradually to the left. Remove the accumulators, separate the parts, and store in column order.

  26. The right-hand support plate.
  27. Stand the machine on its back. Lift the clip at the left-hand end of the detaining toggle release bar 28 and withdraw the bar to the left.
  28. Detach the spring 2.2x9.5x0.23 from the support bar 27 and remove the bell hammer.
  29. Follow the detaining toggle release link in the left-hand column up to the detaining toggle pivot assembly 1. Unhook the left-hand spring (4mm) from the tab on the frame plate.
  30. Follow the detaining toggle arms from the pivot assembly up to the pinned arm on the rock frame actuating shaft 2. The toggle arm is held in place by a slotted link attached to a long 5mm spring. The link has a tapered slot which fits into a groove in the pin. Grasp the link with a strong hook or pliers, pull it forward, and release it from the pin.
  31. Stand the machine on its left-hand side. Remove all the screws from the right-hand support plate, then ease the plate off the ends of the tie rods.
  32. If present, lift out the large L-shaped interlock lever and the attached link and spring pivoted on tie rod H. This interlock is not present in Model H and early Model J machines.
  33. Recover the six short spacers from the ends of the tie rods (including the thin-walled spacer inside the hub of the interlock lever) and store them in the labelled tie rod bags.
  34. Rotate the detaining toggle release bar support 27 to free the arms and lift out.
  35. Lift out the rock frame actuating shaft 2.
  36. Stand the machine on its back and remove tie rod F and spacers. Recover the very short spacer inside the left-hand support plate, and note whether there is a special grooved spacer under the detaining toggle at the left-hand side. Note the location of any shims, and the location of the rock frame actuating shaft support bracket and its short spacer near the centre. The support bracket may not be present on 8-column machines.
  37. Spread the two leftmost frame plates and carefully extract the detaining toggle assembly from its bearings. Detach the large toggle spring 5.0x 70x0.62 from the pin on the frame plate.
  38. Disassemble the clearing handle mechanism on the support plate.

  39. The keys and keyplate.
  40. Invert the machine and set it down on its keys, as previously described. If you have the facilities, measure the wire diameter of the keypiece springs and determine whether they are all the same or graduated by row. If graduated, record the diameter for each row and prepare containers for each size to avoid sorting later. Otherwise, prepare separate containers for the springs from rows 1 to 9.
  41. Stand the machine on its back and remove the keypieces, starting at the top right. Put on your safety glasses, place a finger firmly over the coil of the spring (in case it flies), and unhook the tail of the spring from under the tab on the frame plate. Twist the keypiece to the right, release it from the key, lift out, and remove the spring. Work from right to left, then down, one full row at a time. The keypieces were all identical when new, but may have been "formed" or adjusted in service. The arms are easily re-adjusted, so they can all be stored in the same container. In Sterling machines it is necessary to fully depress the adjacent segment levers in order to remove the 10 and 11 keypieces.
  42. Put the machine back on its feet and lift the keys straight up and out. Start at the front and work backwards in each column. The keystems are often tight as the two operating shoulders pass through the keyplate. Pull on the metal stem, not on the moulded keytop. The step near the bottom of the keystems will often catch on the keystop levers and prevent removal, especially on the 10 and 11 pence keys. Insert a screwdriver from underneath and push the long levers apart to provide clearance. Keep all the pence keys together as they have different numbering to the decimal keys (as does the 1 key in the 10/- column). Stand the machine on its back to investigate any problems.
  43. Remove the keyplate screws behind the 9 keys. Press inwards on the spring clips under the rear corners of the keyplate, then lift the keyplate from the rear and remove. The cork lining will probably be stuck to the tops of the frame plates.
  44. Remove the red Controlled-Key release button and shaft. Some buttons are threaded, others just push on.

  45. The key stops and accumulator interlocks.
  46. Push the central stop wire 33 slightly to the right to unlock the retainer plate on the left-hand side. Push down on the front of the plate to access the key stop wire 13. Push wire 13 half a column to the right, detach the spring from the release plate 14, then lift out the release plate.
  47. Prop the machine up on its back and disconnect all of the long key stop springs from the inaccessible tabs on the side plates. Use two hooks or dental picks, one to push or pull the body of the spring into a suitable position, and one to unhook the spring without deforming the loop. Try not to think about how you are going to get these back on later.
  48. Set the machine back down. Unhook the tops of all the tiny springs between the accumulator locking hook (ALH) and the pinion ratchet reverse lock (PRRL). The springs are at the top front, just below tie rod B.
  49. Detach all the subtraction cutoff lever springs from the tabs on the frame plates.
  50. Withdraw wires 11, 12, and 13 to the left until clear of the right-hand column.
  51. Disengage the hook and tabs at the rear of the upper key stop and lift out. Disengage the lower key stop, turn it 90° to the left and lift out. Remove the ALH, PRRL, and the accumulator latch. Withdraw the wires further, lift the subtraction cutoff lever up, across to the right, then out. Repeat to the end.

  52. The trigger mechanism.
  53. Stand the machine on its back and unhook all the segment lever springs. In Sterling or non-decimal machines, record the variations in length, outside diameter, and wire diameter, or label the springs so that they can be returned exactly to their original positions. Withdraw wires 23 and 24 and remove the springs. (This also releases the brake springs).
  54. Withdraw wire 29 and remove the brake levers and springs.
  55. Lift the clip at the left-hand end of the 1/16" square touch-off bar 31 and withdraw the bar to the left.
  56. Detach the spring from the left-hand end of the touch-off bar support assembly 20. Push wire 32 to the right to clear the left-hand arm of the support. Spread the outer frame plates to disengage the pivots and lift out the support assembly.
  57. Lift the clips at the left-hand end of column lock retainer wires 21a/b and withdraw to the left. Spread the outer frame plates and remove the column lock retainer assembly 21.
  58. Unhook the springs from the column locks on wire 22. Leave the forward end attached to the trigger retainer horizontal (TRetH). Withdraw the wire and remove the locking hooks.
  59. Unhook the small springs from the trigger retainer vertical (TRetV, at the left of each column on wire 32) to the tabs on the frame plates.
  60. Withdraw wire 32 to the left and remove TRetH and V.
  61. At the rear, unhook the rear of the springs from the segment lever bell crank to the trigger connecting link and push the links off the pivot pins.
  62. Withdraw the trigger stop wire 17 and release the forward trigger springs.
  63. Remove the central stop wire 33. On Sterling machines, remove the special short key stop lever pivoted on wire 33 in the 10/- column.
  64. Withdraw wire 18 one place to the left and lift out the trigger assembly. Repeat to the end.

  65. The segment levers.
  66. Remove the left-hand screws in the bottom rear frame tie rods J and K. Invert the frame and lift the two internal feet away from tie rod J. The feet have slots at the forward ends. 8-column machines have only one internal foot. Spread the left-hand support plate to clear tie rod K, then lift the tie rod, spacers, and feet out of the "U"-shaped slots in the frame plates.
  67. Withdraw the key stop lever pivot shaft 25 and remove the pairs of levers together through the rear of the machine. Start a new set of bags or tie wires to keep the long levers together by column.
  68. Withdraw the segment lever pivot shaft 26 and remove the segment and lock levers together through the rear of the machine. Detach the long spring from the bell crank. Turn the bell crank forward across the lock lever, then turn the lock lever 90° and separate it from the segment lever.

  69. The rock frame. Model J rock frame outline drawing
  70. Prepare another set of numbered bags to receive the rock frame parts in column order, or re-use the first dirty set after cleaning their contents.
  71. Open the hinged retainer plates at each of the rock frame.
  72. Withdraw the locking dog stop wire (under the top tie rod).
  73. Hold the first carry gear, spring, and escapement wheel together. Withdraw the carry gear pivot wire one place and lift out the three components together. Release the spring tension carefully, check how far the escapement wheel turns, and record any variations. The initial pre-load on Model J decimal columns was one full turn (1.5 on Model H), but after 90 years it is usually only about 3/4 of a turn. The springs and pre-loads will be different in non-decimal columns. Separate the parts and store in column order. Repeat for the remaining columns.
  74. Turn the rock frame over, withdraw the two detent lever pivot wires, and remove the linked detent levers. The links are intended to be fairly loose.
  75. Withdraw the toggle lever pivot wire and remove the toggle levers and zero stops together.
  76. Make a detailed map of the position of the flanged locating spacers, tie rods, end plates, and especially the arrangement of the short spacers, screws and washers at the ends, then disassemble the frame. The frame plates are all identical (except for the rightmost, which has no locking dog) and do not need to be kept in order.

  77. The main frame.
  78. Devise a fail-proof method of keeping the frame plates in order. There are many subtle differences in the plate fittings that can easily escape notice. A 12-column machine has 14 frame plates and 11 of them are different, so proceed carefully. One method is to scribe a small Roman number in a constant location (eg next to tie rod K) as the plates are removed.
  79. Record the location of the various fittings mounted to the tie rods, including the keyplate clips, front linoleum guards, internal feet, and rock frame actuating shaft support.
  80. Turn the spacers on the remaining small tie rods to loosen them. On Sterling machines tie rod J is in two parts to provide clearance for the high pence keypieces. Withdraw each rod in turn, remove the spacers and any shims present (including the narrow spacers behind the outer support plate), and store them in their labelled containers.
  81. The procedure for disassembling the main tie rods A,B,C, and D depends very much on the condition of the frame and the extent to which it is affected by dried oil and rust. Loosen the screws at the left- hand side, loosen the spacers by turning, and attempt to withdraw the rods to the right. If this fails replace the screws, stand the frame on the left-hand support plate and undo the four threaded 1/4" spacers at the right-hand end. Early machines have round threaded collars; later versions have hexagons. When new, the round collars could be unscrewed easily after loosening the screw at the left-hand end, but after 90 years they may need Vice-grips. Repair any obvious damage to the threaded end of the rod, then remove each plate in order and store the spacers and fittings in the labelled containers. The frame plates are a close fit around the tie rods and must be lifted evenly to avoid jamming.


Please review the general information about cleaning and checking in the Notes on overhauling a mechanical calculator, and proceed as described. Use a large flat-bottomed dish for washing, and be very careful not to bend the long levers or the frame plates. Initial cleaning of all the disassembled parts will take about 6-8 hours.


Please review the material on Reassembly in the Notes on overhauling a mechanical calculator. No special tools are required, but you will need to make some simple spring hooks from suitable fine wire. A pair of strong locking tweezers (or a small surgical artery clamp) will be useful for holding some of the small parts securely during assembly.

Several mechanism wires have retaining grooves which engage with flat spring clips. The clips and grooves are made in matched pairs of several different widths so that the correct wire can easily be found. Temporary follow-through wires can be cut from silver steel or "music wire" of 0.0625", 0.088", and 0.108" diameter from an engineering or hobby supply shop.

In the notes following, tension springs listed as (eg) 3x10x0.3 are 3mm diameter, 10mm closed coil length, and 0.3mm wire diameter.

All parts must be checked thoroughly and lubricated sparingly during assembly. Apply a thin film of oil to steel parts with a (slightly) oily rag to help prevent rust, and apply light oil to all gears, rollers, pivots and bearings.

Reassembly requires patience, care, and attention to detail. If everything goes according to plan, it will take at least 14 hours to prepare and check the washed parts and to reassemble and test the machine.

  1. The frame.
  2. Check the threads and the threaded spacer nuts on the large tie rods A, B, C, and D. These rods have both internal and external threads, and the surrounding material is often distorted. Ease the end diameter and/or the thread profile until the both ends will pass without difficulty through the close-fitting holes in the frame plates, and the nuts can be run fully down by hand. Note that the nuts are counter-bored on the inner face to ensure that the rightmost frame plate is located clear of the threaded section.
  3. Fit screws and washers to the plain ends of tie rods A, C, and D and insert them into the the left-hand support plate. Do not tighten. Lay the plate flat on the bench and assemble the frame plates and spacers in the original order. Fit the special spacers and keyplate clips to tie rod D, and the linoleum guards to tie rod A, all in their original columns. (Look for matching oil stains on the frame plates). Be careful not to damage the keyplate clips while moving the frame during reassembly.
  4. Fit the special nuts. Back off the screws at the left-hand end so that the nuts can run fully down.
  5. Place the right-hand support plate in position and check that the ends of the tie rods are level with or just slightly above the top of the plate. Adjust the nuts if necessary, then loosely fit the 3 screws and washers.
  6. Stand the frame on its right-hand side. Remove the screws on the left side, press the support plate down firmly, and check that the ends of the tie rods are below the top of the frame plate. The tie rod will be pulled up into the washer as the frame is tightened, but must remain clear of the head of the screw. Shims can be added as required to adjust the clearance.
  7. Tighten the screws on both sides. Check that the frame is square and rigid, and that it sits evenly on a flat surface with no twisting or rocking.
  8. Check that tie rod B and the eccentric spacers can be installed and removed reasonably easily. The rod will be a close fit, but should not cause any great difficulty. It must not be loose. Loosen the screws and adjust the frame alignment (or individual plates) as necessary. Remove tie rod B when satisfactory.

  9. Long levers.
  10. Check the two rollers on the segment levers and ensure that they are completely free. Proceed carefully if they are stuck, so as not to loosen the pivot pins. Freeing these rollers is very important, and can take a long time.
  11. Assemble the pairs of segment and lock levers, attach the bell crank springs, and install from the rear. Insert the lower pivot wire 26 (0.108").
  12. Fit the pairs of key stop levers from the rear, passing them between the two arms of the segment lever bell crank. Locate them sideways at the rear by arranging the two short arms on opposite sides of the adjacent frame plate (ie, the outer lever wraps around into the next column). Insert the upper pivot wire 25 (0.108").
  13. Before lifting the frame off the bench, lift the levers and insert any suitable wire through the holes for tie rod F. This will provide a temporary stop to prevent the levers falling through and becoming tangled or damaged.

  14. Triggers, retainers, and column locks.
  15. Start at the leftmost key column. Place the trigger assembly in position with the pinned end with the two springs facing forward. Ensure that the long connecting link passes under the pin on the frame, and that its rear end lies between the segment lever bell crank and the frame to its left. Insert the trigger hanger pivot wire 18 (0.088").
  16. Attach the trigger connecting link to the pin on the segment lever bell crank and connect the spring.
  17. Set the locking plate on the left-hand side to provide access for the lock lever stop wire 33 (0.108"). Pull the front of the trigger forward and down, then push the wire in under the trigger.
  18. Insert the trigger stop wire 17 (0.088") and attach the forward trigger spring.
  19. Repeat for the remaining columns. In Sterling machines, hang the short key stop lever from wire 33 in the 10/- column. The left-hand tab on the lever sits above the trigger.
  20. Push wire 33 further in until clear of the locking plate. Reset the plate and start wire 32 (0.0625") from the left. Place the trigger retainer vertical (TRetV) against the left-hand frame plate, with the curved arm forward and resting on top of wire 33. The hooked end must be in front of the corresponding tab on the rear trigger arm. Feed in pivot wire 32 until flush.
  21. Attach spring 2.9x4.3x0.18 to the tab on the rear of the trigger retainer horizontal (TRetH). Fit TRetH to the right of TRetV. The arms face forward, with the right-hand offset arm passing through the cutout and to the right of the frame plate. The left arm sits above the vertical arm of the trigger. Feed in pivot wire 32 to retain.
  22. Lower the column lock into the column behind TRetH. Pass its hooked arm through the cut-out in the frame plate to the right, bring it back up and sit the hook over the top of the frame plate. Feed in wire 22 (0.088") to retain.
  23. Attach the spring at the rear of TRetH to the left-hand arm of the column lock, and the spring from TRetV to the tab on the frame plate. Repeat for the remaining columns.

  24. Brakes and springs.
  25. Install the brake levers and feed in wire 29 (0.108") to retain. The long arm goes on the right, between the keystop levers and the lock lever, and rests against the rear of the large roller on the segment lever. The short arm passes to the left of the trigger connecting link and helps to hold it onto the bell crank. Keep the brake lever springs at the top and facing rearwards over tie rod C.
  26. Start wires 23 and 24 (0.088") from the left-hand side. The shorter front wire 23 has a groove at the left which engages with a spring clip on the second frame plate. Hang the segment lever springs from the two wires to align with the hooks below, then attach the brake springs to wire 23. Ensure that any different springs are returned to their original locations.
  27. Stand the machine on its left-hand side and connect the springs to the attachment points on the segment levers. Remove the temporary support wire.

  28. Touch-off bar and column lock retainer.
  29. Push the TRetH&V pivot wire 32 to the right until clear of the leftmost column.
  30. Place the touch-off bar support assembly 20 in position near the top centre of the frame plates, with the spring clip on the left-hand side. Spread the outer frame plates slightly and engage the pins on the end of the bar with their bearings. Check that the bar swings freely.
  31. Push wire 32 back home, through the hole in the left-hand arm of the support assembly, so as to limit the movement. Attach the spring 3x7x0.2 from the left-hand arm to the tab on the frame.
  32. Insert the touch-off bar 31 (1/16" square) into the support arms from the left-hand side. Engage the spring clip with the groove in the wire.
  33. Place the column lock retainer bar assembly in position to the rear of the touch-off bar support. The long arm faces forward on the left, and rests on top of the touch-off bar 31. Spread the outer frame plates slightly and engage the pins on the end of the bar with their bearings. Check that the bar swings freely.
  34. Check that the column locks are to the rear of the hooks on the segment levers and are not caught in front. Press the segment lever fully down to correct.
  35. Insert wires 21a and 21b (both 0.088", grooved) from the left through the arms of the assembly and engage the grooves with the spring clips. The forward wire passes under the rearward tabs on the column locks.
  36. Press the rear wire 21b down and check that the locks move rearward. Release the wire and check that the locks remain well clear of the hooks on the segment levers. Push the touch-off bar 31 rearward and check that the locks swing forward to engage with the hooks.

  37. Initial trigger checking.
  38. Check that the segment lever is held fully upwards against wire 33. (If not, the key stop levers are probably too far to the left and caught under the pin on the frame plate). The top of the gear segment should be about level with the bottom of the hole for tie rod B. Check that the key tabs on the lock lever stand higher than those on the segment lever.
  39. Temporarily install tie rod B and the eccentric adjusting spacers. Set the spacers to the half-way position, with the high points of the cams horizontal and facing forward.
  40. Check that the lower rear tabs of all the triggers are behind the hooks on TRetV and are not caught above. Check that the crossways horizontal arms on the triggers are resting on the top of the segment lever. Check that the left-hand arms of TRetH are sitting above the vertical arms of the triggers and are not caught behind. Check that the small horizontal tab at the front of the right-hand arm of TRetH is resting on the vertical projection on the segment lever and not jammed beside.
  41. Check that the pins at the front of the triggers are all in a straight line horizontally and vertically. The tops of the pins should be about level with the top of the adjacent frame plate. If any are out of line, check first that the eccentric spacer is still set correctly. If necessary, adjust the rest position of the trigger by carefully bending the horizontal arm which rests on the segment lever with a suitable tool.
  42. Take a 4 key (or any suitable flat-ended tool) and press down on any pair of key tabs near the front of the segment and lock levers. Check that the front of the trigger moves forward as the lock lever descends, then lifts upwards until it meets stop wire 17 as the segment lever starts to move.
  43. Press down again, and watch the engagement of the left arm of TRetH with the vertical arm of the trigger. The vertical arm starts out under TRetH, then moves forward and clear. Then simultaneously the vertical arm rotates rearwards and TRetH starts to descend. The tip of TRetH must end up sitting exactly on top of the vertical arm of the trigger, with no chance of getting caught behind during the simultaneous movement. This is the "armed" position.
  44. Press down again to bring the trigger to the armed position. Hold this position, then press down slowly on the pin at the front of the trigger. Watch, listen, and feel for two distinct clicks as the two trigger retainers drop into position. (This simulates the keystop disarming the trigger at the bottom of the keystroke).
  45. Press down again to bring the trigger to the armed position. Hold the front of the segment lever against the frame so that it can not move, then release the lock lever. Check that the touch-off bar and the column locks operate correctly. (This simulates a short downstroke). Reset the locks and repeat in each column.
  46. When all is correct, insert tie rod G and carefully fit the plain spacers. Fit the thin spacer and the screw at the left-hand end.
  47. Remove tie rod B and the eccentric spacers.

  48. Key stops.
  49. Check the loops on the free ends of the long keystop springs and re-form if necessary so that they are just slightly open. Check the half-round pins on the bottom ends of the keystops and ensure that they are still firmly riveted to the arms.
  50. Start at the leftmost key column. Fit the smaller keystop into the column with its short right-hand arm over the top of the frame plate. Engage the right-hand tab on the horizontal arm with the hook on the key stop lever. The left-hand tab sits above the trigger.
  51. Turn the larger keystop 90° to the left. Place it over the first, engage the hook, and feed in wire 13 (0.108") to retain. Check that the tabs are still properly engaged. Check that the keystops are free to move and are not jammed against the segment lever.
  52. Repeat for the remaining columns. Remove the support plate to install the upper keystop in the right-hand column. Do not replace the support plate yet.
  53. Stand the machine on its back and connect the keystop springs to the tabs on the frame plates. Use a long wire hook to pull the loop of the spring up against the tab, and a wider tool to push or pull the body of the spring into a position where the loop can be slipped into the hole. Ensure that the loop is fully engaged. Although it looks impossible at first, the springs can all be connected up in about 10 minutes after a bit of practice.
  54. Set the machine on its feet. Insert a 4 key in the first column, between the lock lever and the key stop levers and just forward of the trigger hanger, and engage it with the fourth set of key tabs on the long levers. Press the key fully down and check for smooth operation of the even key stop. Move the key to the third set of tabs and check the odd stop. Correct as necessary, then repeat for each column.

  55. Tie rods.
  56. Be careful not to over-tighten any of the small tie rods. These rods are only 5/32" (3.97mm) diameter with a coarse 4-36 internal thread. There is only 0.023" (0.6mm) of metal on each side, which can easily be damaged (especially on the aluminium rods in later models).
  57. Invert the machine and set it down with the back nearest.
  58. Start tie rod H from the left. Fit the small plain spacer, then the formed spacers with the single retaining tab. The open side of the spacers faces the baseplate, with the single folded tab pointing forward. These spacers must be aligned correctly to avoid blocking the movement of the No. 6 keypieces.
  59. Fit tie rods J and K and spacers. Replace the internal feet and the matching shortened spacers in their original columns. Look for the oil stains on the frame plates to locate the feet, or match the feet with the impressions in the lining of the base. On 8-column machines there is only one internal foot. On Sterling machines tie rod J is in two parts to provide clearance for the 10 and 11 pence keypieces. The left-hand section can be fully tightened, but keep the screw and short spacer for the outer right.
  60. Temporarily replace the right-hand support plate and set the machine back on its feet. Tie rods E and F are not installed yet.

  61. Accumulator interlocks.
  62. Prepare the subtraction cutoff lever, the accumulator latch, the accumulator locking hook (ALH) and the pinion ratchet reverse lock (PRRL) for the leftmost key column.
  63. Hold the subtraction cutoff lever above the active column. Pass its lower end through the top front cutout in the frame plate to its left. Move it down and across to the left into the outer (keyless) column, and engage its right-hand side with the small locating tab on the right of the frame plate. Insert wire 11 (0.088") to retain.
  64. Place the accumulator latch onto the end of wire 11, at the left of the active column. The vertical end passes under the keystop wire 13 and points upwards at the rear. Push wire 11 in until flush with the end of the latch. Push wire 12 (0.0625") through the notch in the subtraction cutoff lever and attach the latch spring 2.8x4x0.18 to wire 12.
  65. Engage the fork on the rear of the accumulator locking hook with the pin on the front of the trigger, then lower the ALH down into position. Push wire 12 into the left-hand arm only, and insert a spare wire from the right to support the opposite arm. On early machines the ALH is located sideways by a vertical tab which engages with a slot in the eccentric spacer on tie rod B. On later machines the ALH has "ears" on the sides to position it between the frame plates.
  66. Check that the small spring 2.8x3.6x0.22 is securely attached between the two holes in the central tab of the pinion ratchet reverse lock. Place the PRRL between the arms of the ALH, with its long arm downwards on the right. Feed in wire 12 to retain. Draw the spring forward and attach it to the bridge of the accumulator locking hook.
  67. Repeat for the remaining columns, then attach the subtraction lever springs to the tabs near the front of the frame cutout. On Sterling machines, the spring for the first Pounds column will be relocated later when the special accumulator latch for the 10/- column is installed.

  68. Accumulators and carry levers.
  69. Replace tie rod B and the eccentric spacers. On early machines, ensure that the vertical tab on the accumulator locking hook is properly engaged with the slot in the spacer.
  70. Set the eccentric cams to the half-way position. On early machines with the ALH locating slot, the high point of the cam must face rearwards. On later machines without the slot it is easier to adjust the cams if the high points face forward. Check that all the segment levers are resting against the underside of the cams.
  71. Check all accumulator parts for dirt or damage, and ensure that the ratchet pawls move freely.
  72. Assemble the accumulator for the leftmost (overflow) column. This accumulator has a plain spacer at the right instead of the pinion ratchet. Place it into position and feed in pivot wire 5 (0.088") to retain.
  73. Assemble the accumulator for the next column. Hold the assembly in tweezers so that the deep cut on the pinion is one tooth forward of the top. Press down on the rear of the accumulator latch to provide clearance, then ease the accumulator up into position. Engage the pinion with the segment rack and feed in the pivot wire. Check the deep tooth alignment and correct if necessary.
  74. Continue to the end. Check again that all the segment levers are fully up and all the deep teeth on the pinions are correctly aligned, one tooth forward of top.
  75. Prepare the backstop, backstop spring, carry lever, and latch lifter for the rightmost column. Check the carry lever very carefully. Ensure that the roller pivot is still firmly riveted and that the roller turns freely. Remove any burrs on the three rearward-facing points so that they can not catch on the lantern wheel. Check that the three riveted levers all move freely, and that the spring(s) are not damaged or distorted.
  76. Start the backstop wire 6 (0.088") from the right-hand side. Place the backstop in position over the lantern wheel and feed the wire into the right-hand arm only. Feed in a follow-through wire from the opposite side to support the left arm.
  77. Hold the backstop spring with the hooked end upwards at the right and place the coils between the two arms. Advance wire 6 through the coils. Note that backstop in the rightmost column has a stronger spring.
  78. Place the carry lever assembly in position beside the backstop and support it with the two wires.
  79. Place the latch lifter between the arms of the carry lever, with the cut-away section of the hub at the top left. Ensure that the longer rearward arm sits under the tab on the accumulator latch lever. Advance wire 6 to the next column and continue to the end.
  80. Support the front of the machine a few inches off the bench. Press the top of the backstop spring back and down with a finger, catch the end from underneath with a fine spring hook, and sit the end of the spring on the edge of the frame plate. Remove your wire, then push the end of the spring to the right so that it hooks over the frame. (If you put the spring in position directly you will have trouble removing your wire). Ensure that the spring is securely hooked over the frame, then continue to the end.
  81. Fit the top front tie rod E and the special formed spacers with the rolled lip pointing upwards at the front. Ensure that the top arm of the carry lever is below the rear of the spacer and not caught above.
  82. Insert the spring retainer wire 8 (0.0625") and attach the carry lever springs. The springs must come off the top of the tab on the carry lever, not from the bottom or side. The front loops should be on the left so that the springs do not rub on the upper arm of the lever. Lift the spacers hard up against the wire.
  83. Lift the bottom rear pawl of the carry lever and push it rearward, so that it passes above the segment lever roller and engages with the lantern wheel. (Lift the ALH if necessary). Temporarily insert the intermediate gear shaft 7, which acts as a forward stop for the carry levers when the segment lever is lowered. Check the the fine torsion springs on the carry lever are still in position.

  84. Accumulator and trigger checking.
  85. While carrying out some of these checks it is necessary to keep the accumulator latch clear of the accumulator gear. Lift the front of the latch with a small hook, or press down on the rear end without touching the trigger. When fully assembled, the latch will be raised automatically by the latch lifter whenever the rock frame is engaged. Perform these checks and adjustments carefully, as most of the mechanism will be inaccessible once the keyplate is installed.
  86. Insert a No. 3 key in the leftmost column, between the key stop levers and the lock lever, with the right-hand shoulder above the third operating tab on the lock lever. Lift the accumulator latch and slowly press the key fully down. Watch and listen for the trigger retainer operation as before. Let the key rise very slowly, and check that the backstop drops over the third lantern wheel bar just as the segment lever reaches the top of its stroke. Adjust the eccentric spacer so that the backstop engages reliably every time, with minimum over-run of the lantern wheel. Check several times to engage with different bars on the lantern wheel. If larger or unobtainable adjustments are needed, it is likely that the pinion deep tooth alignment is incorrect, or the pinions, lantern wheels, and backstops have been mixed and are no longer paired correctly.
  87. Make a full keystroke (down and back). Release the accumulator latch, and check that its forward arm drops fully between the teeth of the accumulator gear. The gear should not move as the latch engages. Adjust the eccentric slightly if necessary, then re-check the backstop operation.
  88. Lift the accumulator latch. Partially depress the key so that the pinion ratchet only advances 2 clicks, then let the key rise slowly. Check that the trigger operates the column locking bar as the lock lever rises. Press down slowly to complete the keystroke, and watch as the keystop presses down on the trigger, just before the key reaches the bottom. Check again that the trigger retainers H and V drop into position at the bottom of the keystroke, with sufficient excess movement to ensure reliable operation.
  89. Lift the accumulator latch and push the carry lever rearwards. Check that it advances the accumulator by one place, and that it returns fully when released slowly. Repeat 10 times to check every bar on the lantern wheel. If the lever stops half-way, check for tight pivots, damaged or mis-placed springs, burred pawls on the carry lever, or damaged bars on the lantern wheel. If these are all correct, increase the clearance for the overrun pawl by setting the segment lever eccentric stop a little lower, then re-check that the backstop and accumulator latch still operate correctly. There is a fairly limited range in which all these adjustments will be correct.
  90. Repeat for the remaining columns. When all columns are working correctly, tighten the screw at the left of tie rod B to lock the eccentrics in position.

  91. Keyboard.
  92. Clean the underside of the keyplate thoroughly, especially where dirt accumulates around the keystem slots. Worn slots are normal, especially on the 3, 4 and 5 keys, but will not cause any problems. Clean the oil holes and tubes thoroughly to avoid carrying dirt into the mechanism.
  93. Check the locating tabs along the front edge of the keyplate and on the frame plates behind the subtraction cutoff levers. Ensure that they all engage cleanly, especially the two small (outermost) tabs which position the keyplate sideways.
  94. Check the small vertical tabs along the tops of the frame plates, and ensure that they are straight. Clean the matching slots in the keyplate.
  95. Put the release plate 14 in position above the keystops, with the fingers facing rearwards from the underside of the shaft. Loosen the right-hand support plate, engage the bearings, and attach the spring 3.5x7x0.3 from the left arm of the plate to the keystop wire 13.
  96. Push the segment and lock levers to the right in each column and the keystop levers to the left, so that the keystems can pass between.
  97. Raise the rear keyplate retainer clips to about 30°. Engage the front of the keyplate under the tabs on the frame plates, then lower the back. Look in from the rear to check that the retainer clips are properly engaged with the lip under the back of the keyplate, then press down firmly. Check that the rear clips are latched to the frame plates, the keyplate sits flat all round, and the tips of all the small vertical tabs are visible and at even heights in their slots in the keyplate. Correct as necessary, then fit the screws behind the 9 keys.
  98. On Sterling machines, start the 11 pence key into its slot and tilt it forward. Stand the machine on its back, spread the lock lever and the keystop levers apart, pass the keystem through, and work the bottom end into position. Insert the 10 key in the same manner.
  99. Prepare the rest of the keys in their colour groups and drop them into the slots in the keyplate. Lift the machine and look in from underneath to investigate any difficulties.
  100. Prepare the keypieces and springs, keeping any graduated springs in their original rows. Wear eye protection while handling the springs.
  101. Stand the machine vertically on its back with a 12mm support under the frame plates. Start at the bottom left as you look at the underside. Check that the 9 keystem passes between the keystop levers and the segment lock lever. Fit the spring to the keypiece, engage the right-hand leg in its slot, fit the hole over the keystem, then engage the left-hand leg. Place a finger over the coil of the spring (to stop it flying off), then hook the tail of the spring under the tab near the left foot. Push the spring fully to the left on the supporting pin so that the coils can not work loose. Proceed left to right across the columns, then upwards, one row at a time.
  102. On Sterling machines it is necessary to fully depress the segment levers around the pence column in order to fit the 10 and 11 keypieces. Note that the empty keypieces in the 10/- and farthings columns are needed to retain the keypieces on their left.
  103. After you fit each keypiece, press the key lightly (until it reaches the resistance of the segment lever) and check for any obvious problems. All keys should have a similar feel and should move easily without any scraping or binding. Further keyboard checks will be made after the rock frame is installed.

  104. Right-hand support plate.
  105. Stand the machine on its left-hand side and remove the right-hand support plate. Examine the support plate carefully and check that the bearings for the release plate 14 and the rock frame actuating shaft 2 are still firmly riveted to the plate. These bearings take a considerable load as the machine is cleared, and sometimes become quite loose. Repair as necessary.
  106. Assemble the clearing handle mechanism on the support plate.
  107. Stand the detaining toggle release bar support 27 in its bearing in the left-hand suport plate, with the clip at the left-hand side and the arms facing straight up into the mechanism.
  108. Stand the rock frame actuating shaft 2 in its left-hand bearing, with the links above the shaft and facing forward. Temporarily insert the link support wire 3 through the frame and the slots in the links.
  109. Check that the left-hand end of release plate 14 is still engaged with its bearing.
  110. Place the remaining short spacers onto their original tie rod ends. Fit the L-lever (if present) over the thin-walled spacer on tie rod H, with the connecting link towards the rear.
  111. Fit the support plate over the tie rod ends. Engage the release plate, rock frame actuator shaft, and detaining toggle release bar with their bearings, and engage the first two with their clearing mechanisms. Check that the support plate sits flat across the spacers. Fit the screws and washers to the large tie rods, making sure that the washers are centred over the rods. Firm up the screws, then check that the release plate, rock frame actuator shaft, and detaining toggle release bar still have a small amount of end play.
  112. Check that the operating arm at the right of the release plate is properly aligned with the clearing cam below, and has no chance of slipping off.

  113. Rock frame detaining toggle.
  114. Stand the machine on its back. Assemble the two parts of the detaining toggle and place in approximate position in the leftmost column, behind the holes for tie rod F. The long link faces rearwards and passes above the central tie rod H.
  115. Connect the detaining toggle to the rock frame actuating shaft. The short forward arm of the toggle attaches to the grooved pin on the operating arm near the left of the actuating shaft.
  116. Spread the frame plates and ease the detaining toggle shaft into the bearing holes 1.
  117. Hold the bell hammer with the spring tab at the top and insert it into the leftmost column, just above the detaining toggle release bar. Feed in a temporary wire 28 from the right to hold. Position the detaining toggle release link to the left of the bell hammer, then insert the grooved wire 28 from the left. Push wire 28 through to the right-hand side and engage the link from the L-lever (if fitted). Check that wire 28 is behind the tails of the brake levers and properly engaged with the clip at the left-hand side. Attach the bell hammer spring to the release bar support.
  118. Take the large spring with the slotted connecting link and attach its free end to the post at the top centre of the leftmost frame plate, just below wire 33. Pull the link forward with a strong spring hook and fit the slot onto the grooved pin at the left of the rock frame actuating shaft.
  119. Attach the left-hand spring from the detaining toggle to the tab on the adjacent frame plate. Attach the right-hand spring between the two arms of the long link.
  120. Fit tie rod F and spacers and tighten the screws. Fit the cylindrical spacer with the reduced centre section (if present) in the leftmost column to provide an over-centre stop for the detaining toggle. Fit the actuating shaft support plate and its short spacer near the centre of the tie rod (look for the oil stain on the frame plates). The support plate is not used on 8-column machines.
  121. Pull the clearing handle forward. Check that the rock frame actuating links move forward evenly on support wire 3, and that the detaining toggle moves positively down onto the stop on tie rod F at the end of the stroke. Press rearward on the detaining toggle release bar 28 and check that the toggle releases promptly and the bell sounds clearly.
  122. Fit the remaining screws to the small tie rods and tighten from both sides.

  123. Rock frame assembly. Rock frame plate diagram
  124. Check the carry lever locking dogs (rivetted to the rock frame plates) and ensure that they move freely.
  125. Assemble the frame plates, spacers, and tie rods according to your map. Alternatively, assemble all the identical plates onto the tie rods and spacers as in the diagram opposite (click to enlarge). Place the two special locating spacers in the centre of the top tie rod with the flanges towards the right. At the left-hand end, fit the two 0.34" spacers to the top two tie rods, then the curved end plate, screws, and washers. At the right-hand end, fit the plate without the locking dog, then two 0.45" spacers and the flat end plate. Fit the 0.125" spacer and screw to the top tie rod, and a screw and washer to the centre rod. Fit the 0.25" spacer and screw at the left of the short tie rod, and a screw and washer at the right. If one of the screws has a thinner head, put it at the left of the centre tie rod. Do not tighten the screws yet.
  126. Place the rear (wide) side flat on the bench with the curved end plate to the left. Fit the pairs of detent levers with their short arms under the clip at the left-hand side. Note that there is a special pair for the leftmost (overflow) column.
  127. Fit the toggle lever and zero stop assemblies into their original columns, with the long arm of the zero stop above (in front of) the carry lever locking dog. If the toggle levers and zero stops have become separated they are best assembled on the end of a spare wire held in a vice, as the torsion springs are quite strong.
  128. Turn the frame over and insert the locking dog stop wire (0.056").
  129. Close the retainer plates at each end and insert the intermediate gear shaft 7 (0.108") through the top holes. Hold the frame against a flat surface and tighten the screws from both ends. Be careful not to over-tighten. Remove wire 7 and open the retainers. Be careful not to twist the rock frame during further operations.
  130. Check that the roller at the front of the carry gear cam turns freely, then assemble the carry gear, spring, and escapement. Wind the spring to restore the pre-load found on disassembly, then hook the escapement arm behind the stop pin on the gear. Fit the assembly into the frame and insert the pivot wire. It will help keep the parts together if you assemble them on a short temporary axle (about 5/8" of 1/16" rod) which can be pushed out as you insert the pivot wire.
  131. Hold the zero stop clear of the carry gear stop pins, rotate the gear by hand, and check that the escapement wheel follows half a turn at a time. Repeat for the remaining columns, then close the retainer plates.

  132. Rock frame installation.
  133. Check again that the intermediate gear shaft 7 (0.108") passes freely through the holes in the top of the rock frame and the corresponding holes in the main frame plates. Correct any tight spots by feeding a 7/64" drill bit in from the end and easing the hole on the side flutes of the drill.
  134. Check that the formed spacers on tie rod E are hard up against the carry spring wire 8. Loosen the tie rod and correct as necessary.
  135. Support the front of the machine about 100mm (4") off the bench. Push rearwards on wire 28 to release the detaining toggle. Press rearwards on the front arms of all the accumulator latch lifters and ensure that the rear arms remain in position up under the latches.
  136. On Sterling machines the 10/- column has an auxilliary clearing interlock lever pivoted on the the actuating link support wire 3. Withdraw wire 3 and let the links drop. Put the auxilliary lever in position with the flanged pin on its right hooked into the corner of the cutout in the frame plate. The high rearward arm passes above the roller on the segment lever. Connect the spring to the bent tab on tie rod A. Rock Frame Locking Wire
  137. Cut a piece of 1/16" rod or wire to slightly less than the width of the rock frame. This will be used as a temporary locking wire to keep the mechanism at zero during installation.
  138. Stand the rock frame on the bench with the forked levers at the top and the carry gears behind. Push the forked end of the right-hand toggle lever rearward against the tie rod, then draw the carry gear upwards until the spring is under tension. Lift the toggle lever so as to engage the zero stop, then insert the temporary wire through the hole in the toggle lever as shown in the illustration opposite. Continue to the end.
  139. Check that all the zero stops are standing at least half-way under the stop pins on the carry gear. Serious misalignment can be corrected by carefully bending the small spring-loaded tabs between the zero stop and the toggle lever.
  140. Do a final check that all the carry gears are still under tension, the carry levers are still engaged with the accumulators, the fine torsion springs on the carry levers are all still in position, and the latch lifters are still rearwards.
  141. Hold the rock frame at each end and carefully insert the lower arms under the carry levers. Rotate the bottom rearwards and move it down and to the left until the leftmost detent lever sits over the toggle link attachment point, as shown for removal.
  142. When the rock frame is sitting correctly, the top will swing easily under the spacers on tie rod E. Difficulties may be caused by incorrect assembly of the tie rod end fittings, the lower arms fouling on the actuating links, the toggle links fouling on the attachment rivets, the carry gear fouling on the forward arm of the carry lever, or the temporary locking wire being too long.
  143. When the rock frame passes under the tie rod, rotate it inwards and upwards and move it further left to engage the lateral locating flanges on the top tie rod with the frame plates. Insert pivot wire 7 (0.108") to support the rock frame, or use temporary 7/64" pins from each side.
  144. Check that the rock frame swings freely back and forth on the pivots. Push the rock frame rearwards and check that all the accumulator latches lift slightly. If any fail to move, remove the pivots, draw the rock frame forward, and push the latch lifter down behind its operating pin. Replace the pivot wires and check again.
  145. Pull the rock frame forward and connect all the toggle links and levers to wire 4 (0.075", with a ring at right-hand side). Remove the temporary locking wire.
  146. Stand the machine on its left-hand side and connect up the rock frame actuating links. Engage the pin on the slotted actuating link with the fork on the rock frame toggle lever. Rotate the actuating shaft slightly to align the holes, then feed the supporting wire 3 (0.088") through the slots in the links and through the auxilliary lever in the 10/- column (if present).

  147. Rock frame toggle testing.
  148. Place the machine back on its feet. Operate the clearing handle and check that the rock frame moves forward and that the detaining toggle locks over-centre. Check that the clearing handle returns freely.
  149. Push rearwards on wire 28. Check that the detaining toggle releases and the rock frame snaps down and rearwards. The rock frame movement must be quick and positive.
  150. Look in from the left-hand side and check that the large carry gear is fully engaged with its accumulator gear.
  151. Clear and release the rock frame again. Examine the small toggle links 4 closely to ensure that they are all fully over-centre. If either end of pivot wire 4 can be pushed down further it usually means that the rock frame is twisted. Correct as necessary so that the rock frame toggles all engage quickly and fully when the detaining toggle is released.
  152. If the rock frame does not engage fully, the problem may be in the actuating links or in the engagement of the gears. The zero position of the carry gear depends on the zero stop levers and the zero studs, which may be loose or damaged. The zero position of the accumulator gear depends on the eccentric spacer setting and the alignment of the pinion deep tooth. Mis-alignment can cause a pair of gears to clash tip-to-tip and prevent the rock frame from engaging properly. Locate and correct any errors before proceeding.

  153. Intermediate gears and numeral wheels.
  154. In Sterling machines, insert the special accumulator latch for the 10/- column. Place the body of the latch into the first pounds column. Pass the plain forward arm under the top rock frame tie rod, then work the rearward end through the hole in the frame plate to engage with the accumulator gear in the 10/- column.
  155. Fit the intermediate gears to their original columns with the flat side to the right. Feed in wire 7 (0.108") to retain, picking up the 10/- latch lever (if fitted).
  156. In Sterling machines, disconnect the forward end of the subtraction cutoff lever spring in the first pounds column and reconnect it to the special accumulator latch lever.
  157. If the machine has coloured numeral wheels, arrange them in order according to the keytops. Check that the wheels spin freely on the pivot wire 9 (0.0625").
  158. Operate the clearing lever. Install the first wheel with the zero near the centre of the curve on the frame plate. Put the front cover in position and check that the zero is slightly offset towards the front of the window. Correct as necessary, then install the remaining wheels in the same alignment.
  159. Enter 8 or 9 in every column and check that the numerals are properly centred in the windows.

  160. Final tests.
  161. Make short gentle keystrokes on every key, moving only the lock lever, and watch carefully for keys that do not return fully. Adjust the keypieces as necessary by careful bending to correct any scraping or binding.
  162. Make several full keystrokes on each key and check that the mechanism operates as expected. Check that the tens-carry proceeds into the next column. Make incomplete strokes and check the operation of the touch-off bar, column locks, and release button.
  163. Enter 999...999, or the maximum capacity in all columns on non-decimal machines. Add 1 in the rightmost column and check that the ripple carry proceeds quickly and smoothly across the whole register.
  164. Check the subtraction cut-off operation in each column. Enter 9 (or the maximum capacity of the column), press and hold the subtraction cutoff button, and add 1. Check that the numeral wheel advances to 0 without producing a carry.
  165. Check the adding, carry, and duplex operation by adding all the (decimal) numbers on the keyboard, 3 at a time. Start with the leftmost three 9s, then the 8s, and so on down the column, then the next three columns, etc. The result should be 499...995.
  166. Test extensively. Correct any defects, and exercise the machine regularly.

  167. The case.
  168. Clean the inside of the case panels and polish the outside. Remove or replace any damaged or deformed linings. Take care not to over-tighten the small screws when reassembling the panels to the base.
  169. Cut a new tranparent window for the numeral wheel cover from suitable clear packaging material (eg the top of a shirt box). Cut new cork or neoprene feet (19mm discs) from 3 or 4mm sheet and glue in position on the underside.
  170. Remove the clearing handle. Invert the machine and set it down gently on a soft cloth. Carefully fit the base and sides and fasten with 4 countersunk screws near the corners. Set the machine back on its feet and fit the front cover and the clearing handle.

Problems in assembly.

Many of the potential problems have been addressed in the relevant sections of the notes, but there are plenty more things that can go wrong. Problems are much more likely if the parts have not been kept in column order. Here are a few of the more subtle problems that may result from errors or oversights in assembly:

  1. A column usually works but sometimes blocks, especially if operated slowly. This is usually due to friction or interference preventing a key from rising fully. The key must rise right to the top of its travel in order to reset the trigger and release the pinion ratchet reverse lock. Likely causes are:
  2. A column was working, but is now blocked. This may be due to a spacer on tie rod E being knocked out of position while handling the machine, so that the rear edge of the spacer fouls against the intermediate gear. It can also be due to the latch lifter not being properly engaged with the operating pin on the rock frame, so that the intermediate gear catches on the edge of the cut-away section of the latch lifter hub.
  3. A column has keys 2 to 9 blocked, but the 1 key operates correctly. This is caused by the rear of the 1 keystem pressing against front edge of the upper keystop and holding it engaged with the segment lever. The segment lever can only move down as far as the first stop, which is sufficient for the 1 key but not for any of the others. Remove the 1 key and carefully increase the curvature - concave side towards the rear.
  4. A column passes from 9 to 0, the carry lever makes a full stroke, but the carry does not happen. The subtraction cutoff lever may be stuck and in contact with the underside of the carry lever pawl, or the pawl spring may have been displaced during rock frame installation.
  5. A column passes from 9 to 0, the carry lever is released, but is unable to complete its rearward stroke. This is usually due to excessive friction, or incorrect balance of spring tensions. Check that all the register compnents have a small amount of sideways movement and are not jammed between the frame plates. Check that the carry lever spring is attached to the top of the lug on the carry lever and not twisted from the side or back. If these are correct, it is likely that incorrect carry springs or preloads have been installed in either the carrying or receiving columns, or that the carrying spring is fatigued. These problems are more likely in non-decimal columns.
  6. A variant of the above is when the column carries correctly if the receiving column is at zero, but fails with high numbers. This indicates that the carry spring is able to overcome friction and the preload of the receiving column, but has not stored sufficient energy to overcome the increased spring tension as the count advances. Increasing the pre-load may help, but may create the same problem for the column on the right. Incorrect springs and pre-loads can also lead to a situation where the force of the segment lever springs, divided by the lever and gear ratios, is insufficient to wind the carry spring as the count increases.
  7. Many intermittent errors can occur if the carry lever does not return promptly, or does not latch correctly under its locking dog at the end of its return stroke. When the column is operated the overrun detent may pull the carry lever rearward, causing an erroneous carry into the next column. Check first that the locking dog is free to move, and that the carry lever spring has not been stretched or damaged. If these are correct, the problem may be due to the segment lever zero position being set too high. Insufficient clearance between the lantern wheel and the segment lever roller results in the carry lever spring having to overcome the overrun pawl torsion spring as it attempts to pull the carry lever forward. Adjust the eccentric stop to lower the segment lever slightly, then re-check the backstop and accumulator latch.
  8. The previous problem is more difficult if it occurs in the leftmost (overflow) column, as there is no segment lever to adjust. (The pawl slides over a fixed pin attached to the frame plate). Remove the rock frame and polish the sliding surfaces, or ease the top of the pin slightly to provide clearance.

Ongoing maintenance

  1. The best way to keep a Comptometer in good working order is to exercise it regularly, and to re-lubricate whenever it shows signs of slow or sticky operation.
  2. Exercise the machine by adding all of the (decimal) numbers on the keyboard, 3 at a time. Start with the leftmost three 9s, then the 8s, and so on down the column, then the next three columns, etc. The result should be 499...995. Add 1 five times and check that the ripple carry proceeds quickly and smoothly across the whole register.
  3. Lubricating the cross-shafts of a Comptometer is done with a set of follow-through wires of 0.0625", 0.088", and 0.108" diameter. Clean the 1/16" wire, apply a drop of oil to the front, and use it to push the numeral wheel pivot wire 9 out of the machine. Clean the original wire (with fine emery cloth if necessary), apply a drop of oil, and push it back from the opposite direction. Repeat as necessary until the wire comes out clean.
  4. Repeat the same process with wires 5, 6, and 7.
  5. To clean and lubricate the carry gear pivot wire in the rock frame, the intermediate gear wire 7 must be replaced with a temporary follow-through wire. The temporary wire must be shorter than the rock frame, so that the two hinged retainer plates at the ends can be opened at the same time. Then follow the same procedure.
  6. Wires whose parts have more limited movement can be withdrawn less frequently, or lubricated directly with a small artist's brush. Do not withdraw any wires (eg 13) that are also used as spring anchors.
  7. Invert the machine and apply a small drop of oil to the side of each lantern wheel, so that it runs in and lubricates the pinion ratchet.
  8. Use a small artist's brush to apply a minimum amount of oil to the other moving parts, pivots, and bearings, including the carry lever locking dogs and the rock frame toggle links.
  9. Exercise the machine again to distribute the oil before replacing the covers.

Original text and images Copyright © John Wolff 2004-2022.
Last Updated: 18 March 2022

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