Archive for April 22nd, 2010

Abusing a Leather Punch for Manhattan-Style Circuit Construction

I’m building a crystal parameter measurement fixture and decided to use Manhattan wiring, rather than an etched circuit board, because I think this will be a rarely used gadget… and it’s RF, so air-wiring is a Good Thing.

The key to Manhattan construction is having a pile of little circuit-board pads that you glue to a ground plane, then solder component leads to the pads. A bit of rummaging turned up an old leather punch / snap crimping tool that’s probably older than I am. After punching a few pads, though, I realized that the die hole had a constant diameter: no relief behind the cutting edge.

Aligning to the die

Aligning to the die

That meant the circuit board pads jammed tight in the hole. Extracting them required a pin punch and far more hammering than seemed reasonable, not to mention far more force to operate the punch than I was willing to apply.

So I found the largest transfer punch that would fit in the die hole, chucked it in the drill press, and aligned the table so the vise grabbed the tool directly in line with the spindle.

The tool is soft steel, intended for leather, so I could get away with the next step: chuck up a drill a few mils larger than the die hole and drill it out to within about 1/8 inch of the cutting edge.

Worked like a champ: the pads no longer jammed in the hole and the tool operated with much less force.

Nevertheless, I shrank some glue-lined heat stink shrink tubing around the handles to cushion the sharp inner edges. The handles are just folded steel, as nobody expected the retraction stroke to require much effort at all.

Padded handles

Padded handles

That helped a lot, as did a few drops of oil in the obvious spots.

The end result was a pile of punchies poked from a chunk of 32-mil double-sided circuit board.

Punch with circuit-board punchies

Punch with circuit-board punchies

Now, to start soldering…

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