Release Shaft Problem

Background

The release shaft, there are two: one for the handstroke and one for the backstroke, acts to control the motion of the program drums. As the drum is rotated by the ratchet lever, when the motion is completed the drum is kept in position by the release ratchet which is mounted on the release shaft. The release lever, at the other end of the release shaft, is moved when the limit dial (#747) is moved by the pointer (#752) engaging with the pin in the dial. This movement, although slight, is transferred along the shaft to the release ratchet which moves away from the ratchet wheel and is held off by the knife blade (#616). As a result, the program drum returns to its starting position under pressure of the return spring (#756).

The problem that has arisen is that the release ratchet is no longer firmly attached to the release shaft and can become displaced. If this happens, then the result is that the drum is released immediately and never moves beyond the first position.

Photo of the release shaft. The release ratchet is the lever at the right hand end of the shaft.

Proposed solution

The main problem in fixing this is that the alignment of the release ratchet, relative to the release lever, is crucial. It is fairly easy to set this with the shaft in position, but the simplest method of fixing the ratchet to the shaft would be to use a modern engineering adhesive (Loctite). However, the problem is that Loctite hardens very quickly when the parts are placed in contact and it takes several minutes to re-install the shaft. By the time the shaft was in place the glue would have hardened enough to prevent the ratchet from being moved into the correct alignment.

My solution to this, after a couple of weeks mulling over the problem, was to make a small jig which could be clamped onto the shaft and provide a reference so that the ratchet could be glued, applied to the shaft and aligned within less than a minute.

parts of jig
Parts of the jig - two plates, with a groove in the larger and two screws to clamp them together over the shaft. A modified screw (half the head removed) is fixed into the side of the larger plate.

jig on shaft
The jig clamped onto the shaft. This can be done with the shaft installed and the ratchet aligned correctly. By carefully locating the modified screw against the ratchet, the plate can then be clamped by tightening the screws. The shaft can then be removed from the machine so that the ratchet can be removed, glued and returned against the locating screw. After a few minutes for the glue to harden, the jig can be removed and the shaft re-installed. A couple of very small flats should be made on the shaft to ensure that the glue is not squeezed out of the joint - Loctite recommend 0.005" clearance, but as this is not a high-torque situation, a couple of small flats should provide enough area for the glue to create a reasonable bond. If the ratchet ever needs to be removed a little heat will break the bond and release it.

Results

On a visit to the machine on 22nd October, 2010, I was able to set up the shaft and fix the jig at the correct angle. The shaft was then removed and cleaned with fine emery paper. The inside of the ratchet was cleaned using a small round file. A few strokes with a square needle file were applied to produce flats on the shaft and then Loctite 603 was applied and the ratchet quickly aligned against the jig.
shaft with ratchet fixed

The shaft was then set aside to allow the glue to harden. Later in the day I re-installed the shaft and found the alignment to be correct. Unfortunately, I was running out of time at this point and so I was not in a position to fully test the fix. I am confident that this should be satisfactory, and will run some tests on my next visit.

Page Created by Bill Purvis. Last update 24th October, 2010
Contact me at: bill 'at' billp.org

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