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:

• TOTAL: Print the accumulated total and clear the accumulator. This is the only way of clearing the accumulator. The total is identified by a "*" on the right of the paper tape. To use this key and the SUB-TOTAL key, they must be held down (normally by the thumb) at the start of the pull of the operation crank.
  
  
• SUB-TOTAL: Print the accumulated total without clearing the accumulator. A sub-total is identified by an "S" on the paper tape.
  
  
• (MINUS): Subtract of course, instead of add. The number is printed in red with a "-" sign on the right.
  
  
• NON-ADD: Print the number from the keypad without adding it to the accumulator. Such an entry is identifed by "N" on the paper tape. Presumably used for item numbers or such.
  
  
• RP'T: Repeat. Inhibits the clearing of the keypad after an add or subtract, so a keypad entry can be used repeatedly, without having to re-enter it. This key locks when pushed down and must be manually released.
  
  
• COR: Correction. Clear the keypad, the MINUS key and NON-ADD key.

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.