Preparing an old set of piano keys for new key tops is a critical operation. I designed and built this router jig to perform the operation of keytop planing with accuracy and speed. To preserve the geometry of the piano action, 1 mm will be planed from the key to account for the difference in thickness between the old ivory key top and the new plastic key top. This also produces a good flat glue surface for the new key top and a nice square notch at the rear for a professional appearance. The old ivories needed to be replaced because of extensive cracking, chipping, and missing pieces.
The photo to the right shows the key after exiting the jig. Note that the clamping mechanism is a simple, quick lever which holds adequately and keeps the process moving. The loose plate between the key and lever is coated on the lever side with some beads of hot glue, to provide gripping surface that would not be present in the hard maple. The router bit is a 1-1/2 diameter flat cutting bit. Since the key is less than 1 inch across, this diameter provides a cutting surface for both left side and right side of the key. Order of operation is:
1) With jig against right shoulder insert into about 1/4 inch. move to the left to plane the front edge of of the key (and the existing key front).
2) Slide the sled in to plane the left side of the key.
3) Move the sled to the right, forming the nice edge at the back of the key.
4) Pull the sled out to plane the right side of the key.
This order of operation will provide for proper rotation orientation of the cutterhead and produce a splinter free surface.
The objectives of accuracy and speed are met. This set of 52 keys was planed in 45 minutes.