DIY Paper Tape Punch - Mechanism diagram?

[Paul Koning]

> On May 1, 2020, at 3:17 AM, Tony Duell via cctalk <cctalk at classiccmp.org> wrote:
> 
> On Fri, May 1, 2020 at 5:02 AM Anders Nelson via cctalk
> <cctalk at classiccmp.org> wrote:
>> 
>> Hi all,
>> 
>> I've had a paper tape reader for a while but never had a punch to make new
>> tapes, and the ones i've found are not only very large but also very
>> expensive. So I'm toying with the idea of making an open-source punch, but
>> I can't find any detailed diagrams of how the mechanism works.
>> 
>> I'm assuming (without any data to back it up) that there is a cam, an array
>> of spring-levered pins, and horizontal spacers controlled by solenoids that
>> bridge the gap between the cam and each punch pin when called for.
>> 
>> Does anyone have insight into how reliable/fast paper tape punches work?
> 
> There are 2 basic designs....
> 
> The mechanically simpler one has a solenoid that directly operates
> each punch pin. The well-known Facit 4070 is of this design, using
> rotary solenoids and drive levers (I am sure the service manual and
> parts list (which contains the exploded diagrams) are on-line. Another
> example of this type is the Heathkit H10 which uses normal linear
> solenoids.
> 
> More common is to have a motor driven crankshaft moving a little frame
> up and down. This goes over the ends of the punch pins and has a
> bracket to pull them down at the end of the punch cycle. Solenodis
> (quite small solenoids, almost like relay coils) move spring metal
> strips (normally called 'interposers' in the manual) into said frame
> under the punch pin so that the pin is then forced up and through the
> tape as the frame rises. The Teletype BRPE, GNT34, many Data Dynamics
> punchs, etc are of this design (to name the ones I can see without
> getting up).

A variation of the second version uses a lifting mechanism for the pins that has a "knee joint" in it.  In the resting position that joint is slightly bent so the cam force merely bends it further, the way your leg does when you knee is flexed.  The solenoid pushes the joint sideways, locking it, like a locked knee, and now the cam will drive the punch pin up.

> Be warned that making any paper tape punch is going to be non-trivial.
> Grinding and hardening the punch pins and making the die block for
> them to run in is quite a difficult machining task. And that's needed
> what ever drives them.

True.  At least the pins may be something you can buy: pin gauges are made to extreme precision in 0.001 inch increments and may well work.  Or metal dowel pins, if they come that small.  But that still leaves the die block.  Would drilling and reaming be good enough?

	paul