John Wolff's Web Museum
Rebuilding the Model J Comptometer
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
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:
- Print a copy of these notes, and tick off each step as it is
- 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.
- 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.
- Remove the clearing handle.
- Remove the two screws in the numeral wheel cover. Pull the cover
forward and remove.
- 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.
- 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.
- Set the machine back on its internal feet.
- The rock frame.
- Replace the clearing handle and clear the machine.
- Withdraw the numeral wheel pivot wire 9. Remove the numeral wheels
and store them in column order in the numbered containers.
- 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
- 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.
- 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).
- 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.
- 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.
- 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.
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.
- 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
- The accumulators.
- 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
- 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.
- 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.
- Withdraw the accumulator wire 5 gradually to the left. Remove the
accumulators, separate the parts, and store in column order.
- The right-hand support plate.
- 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
- Detach the spring 2.2x9.5x0.23 from the support bar 27 and remove
the bell hammer.
- 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.
- 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.
- 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
- 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.
- 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.
- Rotate the detaining toggle release bar support 27 to free the
arms and lift out.
- Lift out the rock frame actuating shaft 2.
- 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.
- 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.
- Disassemble the clearing handle mechanism on the support plate.
- The keys and keyplate.
- 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.
- 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.
- 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.
- 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.
- Remove the red Controlled-Key release button and shaft. Some
buttons are threaded, others just push on.
- The key stops and accumulator interlocks.
- 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.
- 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.
- 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.
- Detach all the subtraction cutoff lever springs from the tabs on
the frame plates.
- Withdraw wires 11, 12, and 13 to the left until clear of the
- 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.
- The trigger mechanism.
- 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).
- Withdraw wire 29 and remove the brake levers and springs.
- Lift the clip at the left-hand end of the 1/16" square touch-off
bar 31 and withdraw the bar to the left.
- 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.
- 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.
- 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.
- Unhook the small springs from the trigger retainer vertical
(TRetV, at the left of each column on wire 32) to the tabs on the
- Withdraw wire 32 to the left and remove TRetH and V.
- 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.
- Withdraw the trigger stop wire 17 and release the forward
- Remove the central stop wire 33. On Sterling machines, remove
the special short key stop lever pivoted on wire 33 in the 10/-
- Withdraw wire 18 one place to the left and lift out the trigger
assembly. Repeat to the end.
- The segment levers.
- 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.
- 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.
- 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.
- The rock frame.
- Prepare another set of numbered bags to receive the rock frame
parts in column order, or re-use the first dirty set after cleaning
- Open the hinged retainer plates at each of the rock frame.
- Withdraw the locking dog stop wire (under the top tie rod).
- 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.
- 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.
- Withdraw the toggle lever pivot wire and remove the toggle levers
and zero stops together.
- 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.
- The main frame.
- 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.
- 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.
- 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.
- 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
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 frame.
- 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.
- 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
- Fit the special nuts. Back off the screws at the left-hand end so
that the nuts can run fully down.
- 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
- 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.
- 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.
- 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.
- Long levers.
- 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.
- 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").
- 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").
- 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.
- Triggers, retainers, and column locks.
- 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").
- Attach the trigger connecting link to the pin on the segment
lever bell crank and connect the spring.
- 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.
- Insert the trigger stop wire 17 (0.088") and attach the forward
- 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.
- 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.
- 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.
- 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.
- 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.
- Brakes and springs.
- 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.
- 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
- Stand the machine on its left-hand side and connect the springs
to the attachment points on the segment levers. Remove the temporary
- Touch-off bar and column lock retainer.
- Push the TRetH&V pivot wire 32 to the right until clear of the
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- Initial trigger checking.
- 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
- 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.
- 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
- 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.
- 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.
- 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.
- 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).
- 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.
- 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.
- Remove tie rod B and the eccentric spacers.
- Key stops.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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
- Tie rods.
- 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).
- Invert the machine and set it down with the back nearest.
- 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.
- 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.
- Temporarily replace the right-hand support plate and set the
machine back on its feet. Tie rods E and F are not installed yet.
- Accumulator interlocks.
- 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.
- 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.
- 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.
- 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
- 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.
- 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.
- Accumulators and carry levers.
- 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.
- 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.
- Check all accumulator parts for dirt or damage, and ensure that
the ratchet pawls move freely.
- 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")
- 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.
- 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.
- 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.
- 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.
- 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.
- Place the carry lever assembly in position beside the backstop
and support it with the two wires.
- 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.
- 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.
- 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.
- 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.
- 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.
- Accumulator and trigger checking.
- 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.
- 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.
- 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
- 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.
- 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.
- 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.
- 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
- 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.
- Check the small vertical tabs along the tops of the frame plates,
and ensure that they are straight. Clean the matching slots in the
- 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.
- 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.
- 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.
- 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.
- 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.
- Prepare the keypieces and springs, keeping any graduated springs
in their original rows. Wear eye protection while handling the
- 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.
- 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.
- 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.
- Right-hand support plate.
- 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.
- Assemble the clearing handle mechanism on the support plate.
- 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.
- 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.
- Check that the left-hand end of release plate 14 is still
engaged with its bearing.
- 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.
- 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.
- 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
- Rock frame detaining toggle.
- 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.
- 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.
- Spread the frame plates and ease the detaining toggle shaft into
the bearing holes 1.
- 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.
- 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
- 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.
- 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.
- 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
- Fit the remaining screws to the small tie rods and tighten from
- Rock frame assembly.
- Check the carry lever locking dogs (rivetted to the rock frame
plates) and ensure that they move freely.
- 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.
- 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.
- 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.
- Turn the frame over and insert the locking dog stop wire (0.056").
- 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.
- 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.
- 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
- Rock frame installation.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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.
- 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).
- Rock frame toggle testing.
- 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.
- 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.
- Look in from the left-hand side and check that the large carry gear
is fully engaged with its accumulator gear.
- 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
- 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.
- Intermediate gears and numeral wheels.
- 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.
- 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).
- 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.
- 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").
- 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.
- Enter 8 or 9 in every column and check that the numerals are
properly centred in the windows.
- Final tests.
- 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
- 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.
- 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.
- 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.
- 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.
- Test extensively. Correct any defects, and exercise the machine
- The case.
- 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
- 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.
- 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:
- 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:
- keypieces rubbing together, or holding the key too far to the left
- a mis-aligned spacer on tie rod H preventing the No 6 keypiece
from rising fully
- keystems not passing freely between the keystop and lock levers
- incorrect engagement of the keyplate locating lugs, causing
distortion of the frame and binding of the keystems.
- 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.
- 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
- 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
- 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.
- 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.
- 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
- 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.
- 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.
- 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.
- 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.
- Repeat the same process with wires 5, 6, and 7.
- 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.
- 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.
- 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.
- 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.
- Exercise the machine again to distribute the oil before replacing
Original text and images Copyright © John Wolff 2004-2022.
Last Updated: 18 March 2022
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Model J mechanism