Tools
You will need only three more tools to complete the necessary work on the keys. From top to bottom: a small, flat jewelers file, a round tapered jeweler's file, and
the rear slot jig (see Chapter 35, page 1). You can purchase a set of jeweler's files quite inexpensively from
Amazon.
First, the slots must be cut into the back of each key as shown on pages 17-20 of this chapter. Then, to ease the balance rail hole, place the balance rail punch into the hole from the top surface of the key. Using a hammer, bang the punch into the key until it almost bottoms out. Remove the
punch and try to slip the key onto its balance rail pin. It should be too tight. Take the tapered round file and insert it into the hole on the bottom of the key. Turn it in until its
tip protrudes from the top of the key, and turn it clockwise and counter-clockwise a few times. Check the fit again, and continue until the key fits easily onto its balance rail pin.
If the hole is sized correctly, the key should drop down when you raise its front end 1/4" [6.35mm]. If the key won't drop down, the hole is still too tight. It is helpful to insert the pin of the'
rear slot jig about 3/16" [4.75mm] into the mortise on the top side of the key and rock it forwards (towards the front of the key) and backwards. this will compress the wood in the front and rear
of the mortise, giving the balance rail pin more room to move.