John Wolff's Web Museum - Rebuilding the Odhner 127

John Wolff's Web Museum Rebuilding the Original-Odhner Model 127 Pinwheel Calculator Contents Introduction Disassembly Cleaning Reassembly Original-Odhner Model 127, c.1950 Introduction These notes give a detailed step-by-step procedure for a complete disassembly and reassembly of the Original-Odhner Model 127 mechanical calculator. The Odhner 127 is a relatively simple and straightforward machine, and is an ideal place to learn the principles on which all pinwheel calculators are based. 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: the Technical Description of the Odhner pinwheel mechanism, which gives an illustrated description of the construction and operation of the basic Odhner mechanism, and the Notes on overhauling a mechanical calculator, which describe general techniques for disassembly, cleaning, and rebuilding. 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 enquiry form. Disassembly Please review the material in the Notes on overhauling a mechanical calculator before proceeding. It is suggested that you print a copy of of this procedure, and tick off each step as it is completed. The normal disassembly procedure following can be completed in an hour or two, provided that no major problems are encountered. If problems do arise (eg the shift mechanism is inoperable, the carriage is stuck, or it fouls on the rotor or other mechanism), an alternative procedure is provided at the end. The normal procedure should be used whenever possible. Preliminaries Remove the top and side covers. Remove the four special screws and washers in the rubber feet and lift off the bottom cover. Remove the carriage stop pin (2 screws from underneath). Hold down the carriage release tab (at the bottom of the shift mechanism) and slide the carriage out to the right-hand side. Remove the back cover, bracing plate, and quick-clearing comb. Pull off the carriage shift buttons and remove the cover from the shift mechanism. Main body Remove the rotor bearing and cap from the left-hand side plate. Remove the rotor bearing from the right-hand side plate. Recover any shims stuck to the face of the bearing or remaining behind on the shaft. Lift the rotor to disengage the locking ring at the right-hand side, then lift the left-hand end up through the channel in the side plate and remove. Remove 2 screws from underneath into the left-hand side plate. Ease the side plate up off its dowels and remove. Remove the circlip and the counter drive gear. Remove 2 screws from underneath into the right-hand side plate. Remove the side plate from its dowels and set aside. Remove the bell and interlock assembly (3 screws). There is generally no need to disassemble this unit further unless repairs are necessary. From underneath, remove the short axle, two levers, and the quick-clearing pin and spring in the bushing at the rear. Remove the carriage shift mechanism and disassemble. Remove the carriage retainer strip at the top front of the baseplate. Right-hand side plate Unhook the return spring and remove the sliding interlock plate and shaft from the side plate. Support the front face of the winding handle and drive out the tapered pin from the rear. Withdraw the drive gear and shaft and disassemble the non-return pawl. Press the handle locking pin outwards until the small rolled pin is visible in the collar at the outer end of the handle. Drive out the pin and disassemble the handle. Remove the outer cap and the inner eccentric bush from the handle stop post. Remove the handle shaft bearing and the stop post. Pinwheel 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 collar, then push it inwards. Push the gear and sleeve inwards into the space created and remove the C ring from the outside of the gear. Remove the gear, split sleeve, nut assembly, and the pressed-metal end disc. Remove the circlip from the 3.5mm alignment rod if it is visible at the top of disc 13. (On some versions of the 127 the rod only extends to disc 10). Remove carry wheels 13, 12, and 11. 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. Remove the circlip from the end of the alignment rod if it appears at pinwheel 10, then remove and disassemble the pinwheels one at a time. Be careful of the internal springs on the detent pawls. 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. Carriage Pull off the back-transfer button and remove the carriage covers. If the front cover has an extra screw below the 9th place in the accumulator, be sure to recover the spacer behind. Roll the carriage onto its back. Carefully loosen the 3 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 (1 screw) to retain the detent pins. Roll the carriage forward onto its base. Remove the back-transfer stop plate from the rear of the right-hand end pillar. Remove the screw and washer holding the star wheel shaft to the centre pillar. Push out the shaft and remove the star wheels, the back-transfer assembly and spacers, and the interlock arm and spacers around the centre pillar. 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 (at each end) forward and clear of the registers. Remove the long screw and retainer plate in the centre pillar, then ease the register assemblies up and out. Remove the interlock cam, numeral wheels, shim washer, and metal cup from the counter register shaft. Remove the interlock cam, numeral wheels, and back-transfer release cam from the accumulator register shaft. In order to disassemble the register bearings it is necessary to drive out the tapered pins in the clearing handles, and the parallel cam-follower pin in the accumulator shaft. This carries a significant risk of cosmetic or structural damage, and is best avoided unless repairs are needed. The bearings can usually be washed out well enough in place. If it is necessary to disassemble the register bearings, note that the pin in the counter handle is driven out towards the rear, while the accumulator side is the opposite. Take note of the sequence and orientation of the components removed. 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. Alternative disassembly procedure If the machine is so far jammed that the carriage can not be removed by the normal procedure, remove the four M4 screws from underneath into the side plates, then carefully ease up and remove the sides, back, and rotor as a complete unit. If the carriage is still stuck, remove the shift mechanism and the carriage retainer strip at the front of the baseplate and lift the carriage straight up and out. Then disassemble the components as described above. Cleaning 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 2 hours. Reassembly Please review the material on Reassembly in the Notes on overhauling a mechanical calculator. Moving parts should be lubricated sparingly as they are assembled. Apply a thin film of light 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 wire diameter. Final cleaning, checking, and re-assembly can be completed in about 4 hours if no major problems are encountered. Carriage shift mechanism Attach the 2 springs 3x4x0.26 from the shift pawls on the rear of