Follow-up on key button mortising

[Clark]

Hi,

I traded a set of APSCO keytops for a set of chipped ivories on a 'Bond'
Packard upright for a music store. I thought it would be appropriate to
trade new 0.147" balance rail pins for its 0.089" oblong pins to try out
a tool I had in mind for enlarging the mortices, following a query I
posted here a few months ago about mortising keys and buttons.

My friends from Hubbard Harpsichord showed me the punch they use to
mortise keys with a drill press, once the balance rail holes have been
drilled into the key plank and rail. It is a punch ground with parallel
sides the width of the mortise, and v-notched on the adjacent double
tapered sides to form cutting edges with the parallel sides.

Two suggestions came up in the thread - Ken Jankura described using a
drill bit with a key stick jig mounted in a cross vice or alternately
free-handed, and Newton Hunt invented a tool on the spot using parallel
X-acto chisels attached to a sized shank, also operated with a drill
press. Newton's turned out to be very close to Cesar's tool.


Enlarging an existing mortice allows one to use the original sides as a
guide. In the case of the 0.089" pins the unbushed mortises measure
0.147".

I started with a 1/2" HSS rod and ground a tip with two sets of parallel
sides measuring respectively 0.147" (the guide) and 0.205" (the width of
the new mortises). I put a 90 degree 'V'  (sharp toward the tip) into
the 0.205" sections, and notched them to form cutting edges with the
flat sides. The narrow sides of the 0.147" section are tapered and
notched in case the key mortises are irregular, and these notches
enlarge at their intersection with the ends of the 0.205" cutting edges
to form additional edges and for clearing waste. So there are 12 cutting
edges in total.

I used a bench grinder, a Sears rotary tool with assorted grinding and
cutting bits, and a couple diamond stones to make this.

It took about 20 minutes to enlarge the mortices nicely with the tool
mounted in the drill press, the throw stop set just to enlarge the
buttons and the table raised to minimize effort. Since the guide
automatically positions the tool and key, no jigs or vises really are
necessary.


Now to figure out how to get the balance rail pins out without damaging
them. ;)

Clark