John Wolff's Web Museum
Rebuilding the Original-Odhner Model 239 Pinwheel Calculator
These notes give a detailed step-by-step procedure for a complete
disassembly and reassembly of the Original-Odhner Model 239 mechanical
calculator. They are also applicable, with suitable modifications, to
the other models in the 200 series, and in principle to any Odhner
machine from the 1920s to the 1970s.
The notes have been prepared and refined during the rebuilding of
a significant number of Odhner machines, and may provide a useful
guide to anyone faced with a similar task. The sequence of operations
described works well for me, but comes with no guarantees as to its
efficiency or appropriateness. No responsibility will be taken for any
consequences arising from the use of these notes by others.
These notes are intended to be read in conjunction with two other
documents in this section:
Please study this material carefully before commencing your overhaul
and refer frequently as you proceed, especially to the illustrations
in the Technical Description.
I would appreciate receiving your feedback, comments, or suggestions
for improvement via the
Please review the material in the
Notes on overhauling a mechanical
calculator before proceeding. It is suggested that you print a copy
of these notes, and tick off each step as it is completed. An Odhner
239 can be completely disassembled in an hour or two, provided that no
major problems are encountered.
- Covers and carriage
- Invert the machine. Remove the four screws and washers in the
rubber feet and lift off the bottom cover.
- Remove the four screws holding the side covers. Slide the covers
downwards at the front, then forward, to disengage the hidden internal
clips. Remove the left-hand cover.
- If the winding handle will turn, remove the handle stop plug and
sleeve (2 special screws from underneath) and remove the cover plate,
otherwise leave until later.
- Remove the top panel (2 screws each side), and the rear panel
(3 screws from underneath).
- Pull off the carriage shift buttons and remove the front panel
(3 screws from underneath).
- Remove the carriage stop pin (2 screws from underneath).
- Hold down the carriage release tab and slide the carriage out to
the right-hand side. If the carriage fouls on the rotor or other
mechanism, leave it and continue.
- Main body
- Remove the rear panel and check dial mechanism and disassemble. Be
careful of the light springs under the detent levers. These are very
springy and can easily be lost during handling.
- Remove the rotor bearing from the left-hand side plate (3 screws).
- Remove 2 screws from underneath into the right-hand side plate.
Ease the side plate up off its dowels and remove the side plate and
- Remove the rotor and disassemble the right-hand side plate.
- Remove the left-hand side plate and disassemble the counter
reversing mechanism. Be careful of the tiny detent ball and spring
inside the right-hand gear (on the short front shaft).
- Remove the bell and interlock assembly and the rotor locking
lever (under the baseplate).
- Remove the carriage shift mechanism and disassemble.
- Pull off the back-transfer button and remove the carriage covers
- Roll the carriage onto its back. Carefully loosen the two screws
holding the metal strip under the accumulator until the spring pressure
is released, then remove the strip and lift out the carry lever detent
springs. Temporarily replace the strip to retain the detent pins. Roll
the carriage forward onto its base.
- Carefully loosen the three screws holding the right-hand end plate
until the spring pressure is released, then remove the screws.
- From the rear, observe that the sheet-metal frame of the tens-carry
mechanism behind the counter register is held in place by a pin near
the top of each side. The pin on the left-hand side is part of the
accumulator star wheel shaft. Remove the screw and washer holding the
shaft to the centre pillar, push the shaft outwards until it is clear
of the carry mechanism, then push out the short pin on the right-hand
side. Lift out the carry mechanism and set aside.
- Remove the back-transfer stop plate from the end pillar (on your
- Remove the accumulator star wheel shaft, star wheels, back-transfer
assembly (disconnect spring), and the bracket and spacers around the
- Remove the 4 screws and narrow retainer plates at the rear of the
accumulator register. Remove the two shafts, carry levers, support
arms, and spacers.
- Roll the carriage onto its back. Remove the retainer strip and push
the carry lever detent pins out of their holes with a suitable wire or
tool. Be sure to recover all 12 pins. Note that there is no detent on
the bell lever in the 13th place.
- From the front, fold the register retainers (each end) forward and
clear of the registers. Remove the centre bearing retainer plate and
screw, then ease both register assemblies up and out together.
- Disassemble the two registers, but keep them separate. Take careful
note of the sequence and orientation of the components as they are
removed from the shafts. Do not remove the hardened pins which operate
against the camming surfaces in the two bearings. In order to remove
the spring-loaded components at the handle end it is necessary to drive
out the tapered pins in the clearing handles. This carries a risk of
cosmetic or structural damage, and is best left alone unless repairs
are needed. The bearings can usually be washed out well enough in place.
- Remove the screw and washer securing the detent lever shaft (at the
right of the centre pillar). Carefully push out the detent shaft and
remove the detent levers, balls, and springs. The balls are sometimes
held by a ring of dirt or oil at the top of the hole, and can spring
away unexpectedly when disturbed.
- Drive out the small rolled pin holding the arm at the outer end
of the back-transfer gear assembly and remove the gears and spacer.
- Counter carry mechanism
- From the rear, remove the circlip and long gear.
- Remove the circlip inside the inner end of the star wheel shaft,
then remove the shaft and star wheels.
- Lift and remove the carry levers.
- Check that the sliding collars are not stuck to their shaft and
correct as necessary. Push out the shaft, leaving the collars and
drive gear behind on the toothed key strip. Remove and separate the
- Remove the spring plates and 7 detent balls from underneath.
- Main rotor
- Loosen the set screw in the round nut at the left-hand end. Wrap
the rotor in a heavy cloth and hold it firmly, then loosen the nut with
a suitable C-spanner (or a length of 4mm drill rod). Alternatively,
grip the round nut in a vice, tighten only as much as necessary, wrap
a rag around the rotor, grip firmly with both hands, and unscrew. The
nut will usually be very tight.
- Prepare a base for working on the pinwheel rotor by drilling a
10mm hole in a block of wood about 100mm square. Stand the rotor
shaft upright in the base.
- Note that the round nut is carried on a threaded collar which can
slide along the mainshaft. Unscrew the nut until it is level with the
end of the thread, then push it inwards. Push the inner gear and the
adjacent wide C ring inwards into the space created. Remove the split
C ring from between the two wide rings.
- Push the outer gear inwards and remove the split C ring from the
recess in its outer face.
- Remove the gears, then remove and disassemble the pinwheels one
at a time. Use plenty of solvent (and patience) if the wheels are
stuck to the shaft, and proceed very carefully to avoid damage to the
die-cast alloy. It helps to withdraw the round alignment rod as soon
as it comes free. Be careful of the internal springs on the
- The driving gear is a press fit on the right-hand end of the shaft.
It can be cleaned well enough in place and does not need to be removed
unless repairs are needed.
Please review the general information about cleaning and checking
in the Notes on overhauling a
mechanical calculator, and proceed as described. Initial washing
and cleaning will take about 3 hours.
Please review the material on Reassembly in the
Notes on overhauling a mechanical
Moving parts should be lubricated sparingly as they are assembled.
Apply a thin film of oil to steel parts with a (slightly) oily rag to
prevent rust, and apply a minimum of light oil to gears, pivots and
bearings. The pinwheels and setting rings should not be oiled.
In the notes following, screws listed as (eg) M3x8 are 3mm diameter,
standard pitch (0.5mm), and 8mm overall length. Tension springs listed
as (eg) 3x10x0.3 are 3mm diameter, 10mm closed coil length, and 0.3mm
Final cleaning, checking, and re-assembly can be completed in about
4-6 hours if no major problems are encountered.
- Carriage shift mechanism
- Attach the 2 springs 3x4x0.26 from the shift pawls on the rear of
the large plate to the hole between.
- Place the long compression springs over the key stems. To make
assembly easier, compress the springs and temporarily tie them shut
with a piece of fine wire or string.
- Insert the key stems into their support bracket with the pins
towards the centre and facing rearwards.
- Place the key bracket onto the flat side of the larger plate.
Engage the pins with the slots in the two shift pawls behind, engage
the locating pins between the plates, and fasten with 2 screws M3x6.
- Attach the 4x8x0.3 spring to the flat end of the carriage release
arm so that it sits above the larger hole.
- Fit the carriage release arm to the rear of the assembly. Attach
the top of the spring so that it lies evenly between and parallel
to the keystems.
- Check that the keys and the carriage release arm move freely, then
release the compression springs and check again.
- Base plate
- Mount the bell and interlock assembly to the base with
3 screws M3x8.
- Locate the carriage shift mechanism on its dowel pins and attach
with 4 screws M3x8.
- Invert the baseplate and install the interlock lever between the
shift mechanism and the interlock plate on the bell assembly. Fasten
the short axle with 2 screws M3x12.
- Right-hand side plate
- Assemble the drive gear and non-return pawl. Note that the pawl is
not symmetrical. Place it on the drive gear with the long pointed tooth
downwards and the side with the more equal spacing on the right. Then
fit the spring washer (bent side down) and the wire retaining ring.
- Fit the winding handle in its bearing. Fit the drive gear with
the long tooth of the non-return pawl facing the centre of the rotor
bearing housing and insert the tapered pin from the top. Check that
the long tooth swings (approximately) equal distances to either side
of the rotor bearing, then support the hub of the gear and drive in
the tapered pin.
- Check that the large pin at the top rear of the sliding interlock
plate is still firmly rivetted in place and correct as necessary. Fit
the shaft into the handle stop pillar and fit the circlip to the
locating pin at the bottom front. Fit the 4x7x0.4 spring from the
plate to the wire retainer (through the hole in the frame).
- Temporarily fit the rotor clearing sleeve, shaft extension piece,
and end plug to the handle stop pillar and secure with the two special
screws. Ensure that the assembly slides freely.
- Left-hand side plate
- Check the gears in the reversing mechanism for damage. The small
pressed-metal gears rivetted to the end plates may be badly worn, or
may have bent or broken teeth if the machine has been forced. Repair
- Place the die-cast side plate flat on the bench with the inner
- Stand the two 5x28 pillars in the rear holes in the side plate,
flanged ends down.
- Place the bright plate with two gears over the pillars, long arm
forward, gears on top. Fasten with 2 M3x12, 1 M3x7, and 3 flat washers
- Check that the spring-loaded pin moves freely in the reversing
- Check that the pointed T-bar in the central body locates positively
in its central detent, and moves smoothly to either side.
- Fit the tiny compression spring 2.2x5x0.5 and 3/32" ball into the
hole in the right-hand end of the reversing body shaft, then fit the
small gear with the cam side inwards and the notch over the ball.
Put on your safety glasses, insert a suitable tool (eg the back of an
Exacto knife blade) between the cam and the gear, press the ball down
into the hole, and push the gear fully home. The ball must rest in the
detent notch in the gear, and not in the gap between the gear and the
cam. The ball will be centred inside the gear and clearly visible from
the outside when correctly fitted.
- Fit the larger cam and gear to the left-hand end of the reversing
body, then the large gear with the counter operating finger. The cam
and the operating finger both face towards the central body.
- Stand the large end of the assembly in the bearing in the
left-hand plate. Fit the slotted resetting arm into the small pivot
hole. Fit two long spacers over the pillars, then fit the top plate.
Insert the third pin and spacer and fasten with 3 screws M3x7 and flat
- Attach the spring 2.8x4x0.3 to the rear of the resetting plate.
- Fit the side plate assembly to the base with 2 screws M4x14. Firm
up but do not fully tighten.
- Pinwheel rotor assembly
- Note that there is one pinwheel each numbered 1 (or 1a) and 6,
but two sets numbered 2 to 5. Each wheel in these sets has two numbers
(2-10, 3-9, etc) and two possible locations for the pairs of carry
pins. Use the numbers next to the installed carry pin. There are two
sets of setting rings numbered 1 to 5, which match the first number
on the pinwheel. The second No.1 ring goes on pinwheel 6.
- Fit the driving gear and flange assembly to the plain end of the
shaft, then fit the thick C ring into the single groove.
- Stand the shaft upright in your block of wood.
- Prepare pinwheel 1, setting ring 1, and pinwheel 2.
- Place pinwheel 1 onto the shaft. Fit the 9 pins, leaving them
slightly outside the edge of the wheel. Place the detent pawl and
spring into position, but do not compress the spring. Place the
setting ring over the wheel, engage the pins with the slot, engage
the hub, then press the detent pawl into position against its spring.
Hold the setting ring and immediately fit pinwheel 2 to keep the
- Hold down pinwheel 2 and check that the setting ring rotates
easily. Sticky operation can sometimes be corrected by reversing or
exchanging the offending pins.
- When the operation is correct, continue in the same manner
to the end.
- Check that the two rows of carry pins progress uniformly across
the rotor, then fit the alignment rod into the holes.
- Fit the end disc with the concave side out.
- Repair the threads on the inner collar where they have been
damaged by the set screw. Fit the round nut so that the shouldered end
of the collar and the set screw hole in the nut are both towards the
- Place the collar assembly, small gear, two wide C rings, and large
gear onto the shaft.
- Fit the first split C ring into the outermost groove on the shaft.
Slide the large gear outwards so that the split ring is held in the
recess in its outer face. Fit the second split ring between the two
wide rings. Tighten the round nut. Tap the assembly on the wooden block
to settle the wheels, then tighten again.
- Operate all the setting rings through their full stroke. The rings
should move evenly over the detents in both directions, with no sign
of stiffness or sticking. Correct as necessary. When all is well,
re-tighten the round nut and tighten the set screw.
- Fit the toothed locking bar and ring from the driving end. Check
that it has no effect when fully inserted, but locks the setting rings
when withdrawn 2-3mm.
- Pinwheel rotor installation
- Check that the two rotor bearings can be inserted easily into
their mountings. Ease any scrapes or nicks around the bearing, or
around the housings in the side plates. The thinner bearing goes
on the right-hand side. Remove the bearings.
Check that the right-hand gear in the counter reversing assembly is
still in its detent position. Rotate the gears so that the timing
marks on their cams (adjacent to the central body) align with the
V-notches in the fronts of the sub-frame plates (see illustration
- Set the handle in its stop and the rotor setting rings to zero
- Hold the rotor with the setting levers one place rearward of
top. Assemble the right-hand side plate to the rotor so that the rotor
locking ring engages with the slot in the large pin at the top rear
of the sliding handle interlock plate.
- Insert the left-hand end of the rotor shaft into the bearing
housing (no bearings yet), and lower the right-hand side plate onto its
dowels. Fasten with 2 screws M4x14, firm up but do not fully tighten.
- Lift the rotor clear of the driving gear and turn it until the
interlock plate on the bell assembly can be lifted into the notch
in rotor end disc. Engage the driving gears and insert the right-hand
- Engage the gears on the left-hand side. Check the timing marks,
correct as necessary, then insert the bearing.
- Check the reversing operation. Carefully make a forward turn and
watch as the counter drive pawl passes through the cut-out in the
rotor shaft. The pawl will foul on the shaft if the assembly is
incorrect, and may cause damage if turned vigorously. Check that the
T-bar has moved to the left, and the timing marks have returned to
their aligned positions. Lift the locking plate again and check that
it resets the T-bar to the centre position. Make a backward turn,
and check that the T-bar moves to the right and resets.
- When all is correct, fit the bearing covers with 6 screws M3x8.
Adjust the end stops temporarily to align the gears - final adjustment
will be made later.
- Rear panel and check dial
- Check that all the detent pawls are free to move. Carefully fit
the springs into their holes and fold the detents over.
- Fit the narrow star wheels onto their shaft and attach with 2
- Fit the numeral wheels onto their shaft with the flat washer at the
left. Replace any shims on the right. Fasten with 2 screws M3x12.
- Assemble the wide star wheels and the long shaft onto the slotted
locating plate and fasten with 2 screws M3x8. Check that the wheels
- Place the star wheel assembly in position, fasten the retainer
strips with 2 screws M3x8, and fit the shouldered screw at the bottom
left. Check that the plate slides freely between the two stops.
- Place the handle in its stop and the setting rings at zero. Turn
the check dials downwards until they stop at zero.
- From the rear, place the panel in position on its dowels. Look
through the rectangular cutout and engage the sliding plate with the
tab on the handle interlock plate. Fasten with 4 screws M3x8.
- Check that the dial operates correctly. If the setting rings are
locked, push the locking bar slightly inwards to release them. (The
locking mechanism can not be finally adjusted until after the rotor
has been aligned with the carriage).
- Carriage preliminaries
- The die-casting alloy can move slightly with time, so it is
advisable to check the carriage alignments first to avoid difficulties
during assembly. Proceed as follows:
- Insert the carriage into the base and check that it moves smoothly
from end to end. Stiff spots will leave tell-tale marks on the
bearing surfaces, which can be eased with a fine file or scraper.
- Fit the carriage positioning rack (teeth down) at the front of
the counter register and fasten with 2 screws M3x8. Check that the
shift controls operate correctly.
- Check the fit of the three register shaft bearings in their
housings. Remove any nicks, scrapes, or spurious die-cast metal to
ensure a smooth fit.
- Check that the detent shaft is straight, and that it can be
inserted smoothly into place at the front of the carriage. Correct
- From the rear, fit the lower 4x70mm shaft, the two star wheel
support arms, and the two spacer washers at the right of the arms.
- Feed in the upper 4x93mm shaft from the right. If the shaft is
tight, ease the holes or file the supporting surface until the fit
is smooth but not loose.
- Temorarily fit the 4 shaft retainers and screws M3x8.
- Check that the star wheel shaft is straight. Check that it passes
smoothly through the outer pillar and the intermediate supports, and
seats properly in the centre pillar. If not correct, try interchanging
the intermediate supports. If necessary, carefully bend the centre
arms until the shaft passes smoothly through all four supports.
- When all alignments are correct, loosen the 4 retainers and remove
the upper shaft.
- Carriage registers
- If the counter clearing handle has been removed, place the bearing
over the shaft, fit the spring into the hollow end, then the narrow
flat washer. Align the holes, compress the spring, and insert
the tapered pin from the front. Looking from the handle end in its
normal position, the clearing teeth should face towards 7 o'clock.
- Fit the pressed-metal cup over the cam and pin, then fit the
shim washer and numeral wheels.
- Fit the interlock cam with the cam facing the end of the shaft.
- If the accumulator clearing handle has been removed, place the
large flat washer over the shaft, followed by the spring, sleeve,
thin flat washer, and the carriage end plate. Align the holes and
insert the tapered pin from the front. Looking from the handle end
in its normal position, the clearing teeth should face towards
- Fit the back-transfer operating lever, forked lifting lever and
wire retainer to the bearing and place onto the shaft.
- Fit the back-transfer release cam with its smaller hub inside the
- Fit the numeral wheels, then the interlock cam with the cam
facing the end of the shaft.
- Place the compression springs and detent balls into their holes
in the carriage frame. Note that the counter detents have shorter
- Feed in the detent lever shaft from the right-hand side. Fit the
register retainer arm (big end down), back-transfer latch, accumulator
detents (short arm vertical at the front), counter detents, and the
left-hand retainer arm. Secure the shaft with 1 screw M3x7 and flat
washer at the right of the centre pillar.
- Open the two bearing retainers, and pull the back-transfer latch
- Check that both register clearing pins are in their normal
positions (at the bottoms of their cams).
- Fit both register shafts into the centre bearing (groove to right).
Align the flats on the end bearings and ease the whole assembly down
into the carriage frame. Keep the handles pointing downwards and the
back-transfer arms pointing upwards.
- Close the outer bearing retainers, fit the centre retainer
(1 screw M3x8), and attach the right-hand end plate (3 screws M3x8).
- Turn all the dials by hand and check the detent and clearing
- Tighten the loop on one end of the 4x7x0.6 spring to fit more
securely on the back-transfer latch lever. Attach the spring to the
rear of the back-transfer lifting arm, draw it under the register,
and attach the loop to the latch lever at the front. Check that the
back-transfer handle raises, latches, and drops correctly.
- Accumulator carry mechanism
- From the rear, feed in the upper 4x93mm shaft from the right and
fit the carry levers, starting with the bell lever (with the extra
tail) next to the centre pillar. Check that the carry levers all
move freely, then tighten the 4 retainer plates.
- Assemble the wide back-transfer gears onto their shaft, hubs first,
then the 3.5mm spacer. Fit the outer arm, align the holes, and press
in the rolled pin. Place the assembly in position behind the register,
with the end of the shaft engaged with the fork in the lifting arm.
- Feed in the star wheel shaft through the end pillar, then through
the register retainer arm, spacer, back-transfer arm, spacer, star
wheels, inner back-transfer arm, spacer, and the interlock arm
around centre pillar.
- Fit the 0.5mm shim washer (if present) between the centre pillar
and the counter side of the interlock arm.
- Fit the M3x7 screw and flat washer into the rear of centre pillar
to hold the accumulator star wheel shaft, but do not tighten.
- Check that the register dials and carry levers all move freely.
It may be necessary to remove the star wheels and ease the intermediate
supports sideways to equalise the clearances along the shaft. The bell
lever in particular must be completely free.
- Fit the back-transfer stop to the rear of the right-hand
side with 2 screws M3x7. Check that the back-transfer gears rise,
latch, and reset correctly.
- Roll the carriage onto its back and drop in the carry lever
detent pins. The wedge at the bottom of the pins must be aligned
horizontally, ie, along the carriage axis. Insert the springs and fit
the retainer strip with 2 screws M3x7.
- Check that the carry lever detents all operate smoothly. Note that
there is no detent on the bell lever.
- Place a straightedge across the carriage base and check that the
edges of the 2 screw heads do not extend beyond the level of the base.
File the screw heads if necessary to ensure that they do not scrape on
the bearing surfaces in the machine base. (You may find 2 of the screws
with heads already chamfered).
- Counter carry mechanism
- Find the sliding collar with the operating fingers closest
together. Place it with the fingers on the bench and pointing to the
left. Line up the remaining collars left to right with the fingers at
gradually increasing angles. The fingers on the rightmost collar will
be facing slightly to the right.
- Hold the key strip with the wide tooth (with the hole) on the
right. Place the drive gear immediately to the left of the wide tooth,
then add the collars in order (right to left) with the fingers
on the right.
- Position the frame with the rear closest (long arms away). Put the
collar assembly in position (left-hand end first) with the gear resting
in the slot in the base. Insert the plain end of the shaft from the
left-hand side, and assist the collars onto the shaft. The last teeth
on the key strip are positioned either side of the right-hand frame.
Check that both rows of fingers are aligned in a uniform progression.
- Be careful handling the assembly prior to installation as the
mainshaft can easily fall out.
- From the front, hold each carry lever with the long end up and the
open side away. Pass the long end up through the slot in the top plate,
fit the open side into the V-groove in the collar, then drop the bottom
end into the slot in the base.
- From the rear, start the plain end of the star wheel shaft from the
left-hand side. Fit the 1.8mm spacer, the star wheels with their hubs
to right, and the 8.5mm spacer at the right. Fit the circlip at the
inside of the left-hand side.
- Fit the long gear and circlip.
- From underneath, fit the seven 3/32" detent balls, two spring
plates, flat strip, and 2 short screws M3x4.
- From the rear of the carriage, push back the accumulator star wheel
shaft until it is clear of the counter side. Check that the curved
counter register retainer arm is in position against the end pillar,
lift the central interlock arm, and insert the carry lever assembly.
Hook the long forward arms over the detent shaft at the front.
- Push the accumulator star wheel shaft inwards to lock the carry
assembly, then insert the shouldered pin from the outer side. Tighten
the retaining screw on the star wheel shaft.
- Installing the carriage
Examine the narrow gear at the outer end of the counter carry
mechanism and locate the tooth marked with a dot on its tip. Align
this dot with the V mark on the adjacent frame (as illustrated).
- Support the front edge of the machine on a small block so that the
rotor interlock lever (under the left-hand side) is clear of the bench.
- Set the winding handle in its stop.
- Lift the back-transfer interlock arm (under the front right-hand
side of the rotor) to its upper position.
- Slide the carriage in from the right-hand side until it stops
against the shift mechanism. Press the carriage release lever and
continue carefully. Look in from the left-hand side and assist the
long gear in the carriage to engage with the driving gear in the
main body. Release the release lever and push the carriage further
until it locks. Re-check the alignment marks and repeat as necessary.
- Temporarily fit the carriage stop pin (under).
- Final adjustments
- Support the front edge of the machine on a small block so that the
rotor interlock lever (under the left-hand side) is clear of the bench.
- Check the operation of the carriage shift mechanism, and ensure
that the carriage is held securely in each position. Set the carriage
fully to the left.
- Set the first and last rotor discs to 9, then turn the handle and
check the alignment of the extended pins and the star wheels. Adjust
the bearing end stops to provide proper alignments with minimal end
play, and tighten the lock nuts.
- Place the top cover in position and check that the setting rings
do not rub on the sides of the slots. Straighten any bent or damaged
slots as necessary.
- Check that the counter drive pawl is centred over the corresponding
- Set the carriage to its leftmost position and check that the
back-transfer gears rise and latch correctly. Adjust the back-transfer
stop and the latch lever if necessary to obtain full engagement
- Check that the left-hand arm of the back-transfer gear assembly
does not foul on the rotor end plate. Adjust the rotor position or
shim the end plate if necessary.
- Check that the setting rings are locked when the handle is pulled
outwards, and that they become free when the handle is in its stop.
Problems may be due to bending of the locking bar and ring, lateral
misalignment of the check dial mechanism at the rear, or stiffness in
the spring-loaded winding handle. Correct as necessary to obtain
prompt and reliable operation.
- Check the operation of the rotor clearing mechanism. Hold the
sleeve on the handle stop pillar inwards with your thumb, pull out the
handle, and turn forwards until it stops (about 1/4 turn). Return the
handle to its stop. It may be necessary to adjust the lateral position
of the sliding gear assembly on the rear panel by bending the
- Set the rotor to zero and the carriage fully to the left. Rotate
the counter clearing handle and watch the movement of the interlock
plate under the left-hand end of the rotor. The tooth on the
interlock plate must rise far enough into the notch in the rotor
end disc to prevent the rotor from turning. The plate must fall back
promptly at the end of the turn. Repeat for the acuumulator side.
Adjust as necessary to correct any problems.
- Give the winding handle a forward turn. Rotate the counter clearing
handle and watch the movement of the interlock plate and the slotted
resetting arm under the counter reversing mechanism. The arm must rise
far enough to reset the pointed T-bar to its central position. Check
again for a backward turn. This movement is frequently inadequate, due
to wear on the cam follower (on the interlock arm around the central
pillar on the carriage). Correct by extending the vertical operating
arm on the interlock plate. A small piece of steel or brass can be
soldered, brazed, or screwed into position to extend the arm by about
2mm, then filed down to give a satisfactory operation. Excessive
build-up will cause binding on the cam.
- The easiest way to get access to the interlock plate while the
machine is assembled is to remove the carriage, remove the four M4
screws from underneath into the side plates, then lift off the sides,
back, and rotor complete. Adjust as necesary and reassemble.
- Check the operation of the back-transfer interlock. Give the handle
a forward turn, then check that the back-transfer lever can not be
engaged. Reset the interlock by clearing the rotor using the sleeve on
the handle stop, then check that the back-transfer gearset rises,
latches, and releases correctly. The interlock is operated by an arm
attached to the handle interlock plate (under the right-hand end of the
rotor), which may be bent as a result of forcing or incorrect removal
of the carriage. Correct as necessary.
- Set the carriage to the left. Set a 1 in the first rotor positon,
crank forwards and backwards, and check that ripple carries operate
smoothly in both directions on both registers.
- Verify all operations with suitable test calculations.
- Finishing off
- Assemble the perspex windows and decimal indicators in the covers.
- Remove the carriage and install its covers with 4 trim screws M3x8.
- Fit the back, front, and top covers (in that order) to the main
body. Replace the carriage shift buttons and back-transfer button.
- Remove the handle stop plug and clearing sleeve. Fit the side
covers, sliding them rearwards then upwards to engage the internal
clips. Tighten the clips first if necessary. Fasten with 4 screws
M3x7. Replace the clearing sleeve and handle stop plug.
- Reinstall the carriage. From underneath, re-fit the carriage stop
pin, and check that the carriage locks securely at each end of its
travel. Rotate the stop pin or adjust the eccentric if necessary.
- Tighten the M4 screws into the side plates.
- Fit the bottom cover and rubber feet. Satisfactory replacement feet
can be cut from 4mm neoprene sheet with a 1.5" wad punch.
Original text and images Copyright © John Wolff 2009-17.
Use at own risk; beware of errors; suggestions for improvement welcome.
Last Updated: 19 September 2017
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