R.C. Allen 805
Key-set Adding Machine

Manufacturer: R.C. Allen
Model: 805
Year: 1930s ?
Functions: Add, subtract, accumulate
Keypad: Full
Digits: 8/8
Display: Dial, paper tape

This is a crank-operated key-set adding machine. Punching in a number and pulling the operation crank prints the number on paper tape and adds it to an accumulating total. The accumulated total is always present in the odometer-type display. Each addend is identified on the paper tape with "<" to the right of the number.

Note the 3-3-2 colouring of the digit columns. There is no actual functional distinction between the groupings but they were intended to demark thousands of dollars, hundreds of dollars, and cents.

The other keys function as follows:

Some history of the R.C. Allen company.

Exposed mechanism from above.

The paper tape mechanism, inking ribbon and operation crank must be removed prior to removing the top cover. The paper tape mechanism is mounted in hidden keyhole slots. To remove it, unscrew a small post off the right end of the mechanism and slide it to the right.

The entire keypad can then be removed as a module for access further inside the mechanism. Removal is quite simple: pull off the six non-numeric key-tops, remove four screws on the sides just below the keypad top and a threaded post on the left near the front. Pushing down a row of keys will hold some sliders in place during removal and re-installation.

The main mechanism lifts off the bottom plate with the removal of another 4 screws.

Exposed mechanism from below.

Right-side view of mechanism.

Left-side view of mechanism.

Rear internal view.

The cylinder at the rear of the machine is a hydraulic damper. The damper is connected to the operation crank. It acts to smooth and dampen the operation of the crank, primarily the stopping forces when the crank returns to the resting position. With the damper the lever can be pulled forward and then simply released for the return stroke.

The screw with nut near the top of the damper is an adjustment for the degree of damping (CCW for greater damping). The two identical screws near the top of the damper are fill holes, one for air release while filling and one for liquid.

The gasket visible on the damper is a homemade substitute. It should be an internal O-ring.

The dismantled hydraulic damper.

The hydraulic damper is a partitioned cylinder filled with fluid and a vane that can rotate through nearly 180 degrees. Rotation of the vane forces the fluid through a constriction to produce the damping effect. The two disks with the 4 holes around the periphery form the constriction. The fluid is forced from the 'full' compartments of the cylinder up through two of the holes, over the partition wall, and down through the other two holes to the 'empty' compartments. The two disks can be adjusted relative to each other by the small cammed shaft to vary the size of the holes and hence the degree of damping.

The damper acts in both directions, but the action is asymmetric. Two one-way valves are formed by the holes and fine metal strips on each side of the vane. On the pull stroke, fluid pushes the strip out adding an additional path for fluid flow, reducing the damping effect. On the return stroke, the fluid pressure holds the strip down and keeps the holes covered.

Exactly what the fluid is (was) I don't know, presumably some type of hydraulic fluid. When I opened this unit it was half-filled with a brown, sludgy liquid, congealed precipitate and deposits on the surfaces. The liquid was only slightly oily and it evaporated fairly quickly. Whatever it was, it was 70-odd years old and quite vile. The main seal is an O-ring (1/16 inch, 1-3/4 ID, 1-7/8 OD), what was left of the original was rock-hard.

The unit was cleaned and I refilled it with 10W-30 oil. I initially tried brake fluid but it was too thin to be very effective.

Rear view.

- Unit Log -

Serial Number: 1095765
Year of Manufacture: 1930s ?
Date of Receipt: 1998
Source: surplus
State upon Receipt: A little grubby but fully functional. Oily liquid in bottom and soaked into acoustic padding on back.
Status: Fully functional except for problem with depressing total keys after carry (see repair 2013 Feb 03).

Date: 2013 Jan 30
Procedure: Lever difficult to pull, particularly on return. Mechanism sticky. Dried sticky grease/oil present. Joints on a main shaft sprayed with lubricated contact cleaner. Still problems with response around carry levers on digits 2? & 5, those bearings surfaces sprayed also.

Date: 2013 Jan 30
Procedure: Total keys will not depress. Subtract key does not release fully, contact surfaces sprayed with LCC.

Date: 2013 Jan 30
Procedure: Unit always subtracts. Add/subtract selector (shaft at front) is not pushed far enough out after subtract to engage for add. U-bracket on A/S shaft (left-front) has somehow been twisted. Straightened.

Date: 2013 Jan 31
Procedure: Hydraulic damper dismantled and cleaned. Cylinder was about 1/2 full with brown sludgy liquid. Liquid smells sickly sweet, slightly oily but evaporates fairly quickly. Hard brown film and sludge on most surfaces. Cylinder seal had turned rock hard. One of four cylinder screws breaks during removal, replaced, screws are 5-44 thread.

New seal cut from bicycle tube, cylinder refilled with DOT3 brake fluid, about 2/3 full. Damping action is present but not known if it is as effective as it should be. Feels like it should be a little stronger. Could try filling it further or use a thicker oil such as 10W-30.

Date: 2013 Feb 03
Procedure: Damper cylinder seal replaced with hopefully better one cut from fiber gasket. Plastic shim washers placed on bottom of vane to raise it, to account for thickness of gasket. Refilled with 10W-30 oil instead of brake fluid, near full to seal level.

Remaining fault: Occasionally, after an addition or subtraction, the total keys will not depress fully. The lever must be pulled for a 'null operation', to reset something before a total can be taken. Seems to correlate with a carry having occurred in the operation. Traced as far the 'copper' digit bars nearer the rear of the machine which are not always being reset fully at the end of an operation.

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Mechanical Calculators