Jack tongues

The tongue fits in the slot routed into the jack body and is kept in place by a small axle pin. A mortise is punched completely through to receive the plectrum.

Holly, a fine-grained wood, was historically one of the commonly used materials for the tongues. I'm sticking with tradition and will be using the sheet of holly seen in the photo that also shows the resawed walnut the jack bodies came from.

First I cross-cut strips 28 mm wide from the sheet. Each strip can be imagined as a bunch of tongues attached together side-by-side, hence the need to cut across the grain. My tongue slot is 30 mm, but I feel the tongues should stop slightly short of the top of the slot so that the tongue doesn't absorb any of the repeated impacts of the jack hitting the jackrail over and over. That might bend the axle or break the tongue. The tongues will be slightly inset from the front face of the jack, instead of being flush.

Once the strips were made, I chamfered one edge at 25 degrees with a chamfering router bit. This edge will rest against the angled bottom of the tongue slot; the difference in angles between the two (25 degrees versus about 40 degrees) gives me some clearance that will be explained shortly.

Next, I needed to mark where the plectrum mortise would be. On some historical jacks, a small groove across the back of the tongue shows the location, and also thins the tongue to facilitate punching the mortise successfully.

I'm placing my mortise 9.5 mm from the top. That location was marked by making a 1/32" groove with a special small router bit. The groove is about 1 mm deep, reducing the thickness that needs to be punched through from 3 mm to 2 mm:


Individual tongues were sawn from these strips at the bandsaw. With a few strokes of sandpaper, the sawn edges were cleaned up.

A finished tongue:


I punched a test mortise on this one, and luckily it worked without splitting. More on making the mortises in the next post.