A friend has need of an Ampico "B" Repeat Switch to replace one he has
which is on the verge of disintegration. I took my own switch, which
is in relatively good shape, to model a CAD/CAM file to use with my
3D printer. In looking at it closely, there is a feature whose purpose
I am at a loss to understand, but one I recall seeing on several other
"B" repeat switches. On the outside surface of the turning disk, just
at one end of the "trough" into which fits the stem retaining pin, is
what appears to be a small, slightly rounded, flush brass pin. A quick
call to my friend, a well-known "B" restoration tech, revealed that his
switch is absent this feature. Moreover, he could not recall having
seen this feature on any of the other "B" repeat switches he has seen.

The inside surface of the disk reveals this to be a blind hole that
"communicates" with one or the other of the two larger elbows in the
body of the switch, depending on which position it is in. Other than
adding a minute amount of volume to the pneumatic circuit, I can fathom
no reason for it. My engineering sense abhors mechanical features with
no discernable purpose. The hole is about the size of a #41 drill bit,
and measurement shows that the brass "plug" may only be 0.009-0.010"
thick. This suggests it was a disk pushed through from the "inside"
with a hemispherical stylus until it was flush with the outer surface.
Please, someone tell me its purpose; restful sleep will elude me until
I know. (Photos attached.)  -J. Grant

 [ http://www.mmdigest.com/Attachments/17/11/23/171123_195225_Ampico_B_Repeat_Switch_Detail-1.jpg

 [ http://www.mmdigest.com/Attachments/17/11/23/171123_195225_Ampico_B_Repeat_Switch_Detail-2.jpg