Pin Strip Drilling Machine

How all those holes get drilled

A Signature Punch comes with a set of six acetal pin strips, each with regularly spaced, closely drilled holes. For each tool there are about 660 holes in total that need to be drilled. This machine does most of the work. It takes 64 minutes to complete a strip with the closest spaced holes (7/64″ on center) and 34 minutes to drill the strip with the widest (13/64″ on center). The machine can be left alone to run and shuts itself off when a strip is completed.

The machine is slow and inefficient but very dependable. A motor, speed reducer and two pulley reductions bring the driving crank down to a speed of one revolution every 26 seconds. This drives the indexing and drill feed mechanism by the use of cords and weights. At the beginning of each cycle a cord pulls on the indexing mechanism drive wheel to advance the pin strip a precise distance. After the indexing wheel hits a stop the cord continues to pull forcing the chuck and bit down to drill a hole. To complete the cycle the process slowly reverses, allowing the drill to lift and resetting the index wheels before beginning the next cycle. I have been using the machine for about 35 years with very little maintenance and with very little scrap produced. The indexing/feed mechanism is driven by an ancient motor coupled with a used industrial speed reducer that I picked up at a rummage sale for $5.00.

A pin strip blank is fastened into a special carriage which will be placed in the machine.

A lead screw pulls the carriage along a precise distance for each cycle. Here the lead screw is shown next to the threaded fitting by which it is connected to the end of the carriage.

A chip breaker keeps the shavings from clumping up around the drill bit.

The lead screw is a standard threaded rod with 24 threads per inch. This ratchet has 8 teeth so one ‘click’ pulls the lead screw 1/192 of an inch. A weighted cord drives the ratchet spindle a set number of clicks to advance the lead screw a precise amount before each hole is drilled. The inner wooden wheel has a movable stop that regulates this. There are 6 different settings to drive the ratchet, from 39 clicks (13/64″ on center, the widest spacing) to 21 clicks (7/64″, the closest spacing).

An electric drill is used to re-wind the lead screw after a strip has been drilled.

A set of pin strips showing the hole spacings.

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