Key Mortise punch
Inserted Into Balance Hole
Top: Original - Bottom: After Using Punch
Place the point of the punch into the balance rail hole, orienting the punch so that the flat side of the triangle is parallel to the sides of
the key. Using a heavy hammer, bang the punch down into the key until it almost bottoms out. Remove the punch, and your mortise is finished.
Place the key onto its balance rail pin on the keyframe. Chances are it will be a little tight. Enlarge the hole slightly at the bottom of the hole
using a small round file. Test the fit several times until the key slides down on the pin.
The punch is relatively easy to make. I made mine out of an old piano tuning pin punch. Using a bench grinder, you grind a 1/2" [12.7mm] high triangle
into the steel. The tricky part is getting the thickness of the triangle to match the thickness of the balance rail pin. With a little patience,
and a lot of measuring with a caliper, success will be achieved. It is much less expensive to make your own balance rail punch. However, if you'd rather not go to this trouble,
just buy a ready made punch from the Instrument Workshop if it's currently available.
(see Suppliers).