Punching the mortises

Each tongue has a little mortise which holds the plectrum that plucks the string. This mortise is made by punching a slot through the tongue from back to front.

The punching setup at the drill press is a reasonably simple affair:


Using the drill press gives me a handle to press the punch down with, and also maintains a consistent punching angle. Jacks tend to work better if the plectra angle upwards slightly, so I tilted the table 5 degrees.

The punch itself is a 2.0 × 0.4 mm micro-screwdriver blade held in a small drill chuck. The tip passes through the slot in the maple block, which acts as a hold-down for the tongue and helps to pry the punch off as it is withdrawn. Underneath the tongue a slice of end-grain maple acts as a firm surface to work on. I set up the jig to punch the slot 9.5 mm from the top of the tongue, exactly at the point where the tongues were previously grooved across the back.

Before and after pictures showing how the tongue is punched:



This setup worked quite well in punching the mortises. The trick is to make sure the punch is not significantly wedge-shaped in profile, or it will split the tongue. I'm pleased to say that not a single tongue out of more than 130 was lost this way.

The one minor flaw I discovered is that the punching operation produces a bubble of compressed wood on the front face of the tongue that I had to slice off with a chisel to reopen the mortise. My end-grain maple wasn't a hard enough surface to prevent this from happening. Perhaps it would have been better to use a piece of metal with a small slot in it to allow the screwdriver tip to pass right through the front of the tongue. Otherwise, this was a creditable first attempt.