I know we've been over this a few times in various discussions, but I'd
be grateful for a recap and to pull a few threads together here.
I'm installing my latest set of jacks, they work beautifully - mostly.
They follow some recommended geometry stated here on the list - 10mm
from bottom of tongue bevel to axle and another 10mm from axle to quill
mortice, with a curved slot for quill angled at 10 degrees upward.
I first put them in and they passed the "slow" test: releasing the key
very slowly the quills slipped backwards beautifully over a still string
- so far so good.
BUT they were lousy at repeating rapidly, what happened is at the pluck
the tongue was thrown backwards - the spring that I used being too weak
to resist the energy of the pluck - and so takes way too long to come
back to rest ready to pluck again.
I have solved the problem by installing "staples" in the back of each
jack a-la KIRCKMAN (nota bene sp - peter!) and the problem is solved,
they work flawlessly. I used 0.020" brass wire and a pair of
needlenosed pliers to form and install the staple around a couple of
tiny pilot holes I made and did the whole rank in an hour: one of those
pleasurable tasks where you feel almost a little lonely to have
The other possible solution would be to increase the strength of the
bristle to resist the tongue though I'm not convinced that this was the
best course of action, it sounds like a recipe for hangers and that we
ought to try for the lightest possible spring that will do the job- ie
facilitate rapid repitition.
Then there's the issue of possible clicks - on the one hand the click of
tongue against staple and on the other the click of tongue against the
bottom of the slot as it comes back home, or I guess the worst of both
worlds two clicks. I haven't installed "anti-click" pads anywhere and
to my ears they aren't required: the test I guess will be once the
whole ensemble is playing whether there are noises that are distracting.