[pianotech] Knuckles Replacement - the details

[Joseph Garrett]

Just finished swapping out the 10mm knuckles for some 9mm ones. As I was
doing it, it occurred to me that the fine details might be of use to those
who have not done this job. So, here they are:
I removed the original knuckles with Fence Wire Cutting Pliers(slightly
modified<G>).  As I did, I cleaned the notches and removed any residual
glue from the shanks & mortises. I did this with Nicholson 4" files, one
with the sides made "safe", the other left as is. It turned out that the
"as is" one was .001" thinner than the "safe" one, which was used as the
final thing to clean out the mortise and size it. The "as is " one was
exactly the dimension of the mortise. <G> Once all the shanks were prepped,
then each individual knuckle was fitted for it's shank mortise and the nap
of the leather was determined. The nap needs to be smooth towards the end
of the shank and rough towards the centerpin. The "rosewood" of the
knuckles is not absolutely the same size, nor are the mortises of the
shanks, so individual "fitting" is needed. Once the knuckle was "fitted",
it was then glued into the mortise. I use modified clothes pins, (the
spring type), to add just enough pressure to hold the knuckle at right
angles to the shank and in the bottom of the mortise, without crushing the
knuckle. At the same time as the gluing process, I double check for damage
from the removal of the other knuckles. If found, I press glue into the
crack(s) and the clamping does a double duty. I have 16 of the clamps, so I
just pull from the first of the shanks, when I get to #16 I use #1. It
seems that the cold hide glue has set up sufficiently in this amount of
time. The work goes fairly quickly, even though I'm doing a bunch of things
to each one of the shanks, in the process. Once the glue is set, I clean up
any glue beads/smears on the outside of the joint(s). Of course, in the
process, I make sure the knuckles are in exactly the proper position in
relation to the shank/motises.
Hope that helps.
Joe


Joe Garrett, R.P.T.
Captain of the Tool Police
Squares R I