I've been practicing repinning and rebushing on my young chang u-121 upright but the unconventional plate with a screw on the butt is throwing my weight testing off. I rebushed then repinned a couple of flanges (having 4 swings as a weight test) then installed them without loosening or tightening the plate and I notice the hammer wobbles side to side too much. So I take the assembly out and tighten the plate down via the screw and then the hammer dosn't have enough swings (only 2). How does one find a good friction when there are these two factors involved? Should the plate be screwed down tight before pinning? Is there a standard tightness for the plate I don't know about? Any thoughts would be helpful. Thanks,

Jordan

I think the butt plate replaces the birdseye in this action (right?), so the center pin (CP) shouldn't move at all against the plate; it should only rotate in the bushing (where there's felt).

In a normal bushing, you always size the center pin to the birdseye, then fit the bushing to the pin (by reaming if it's tight, by rebushing if it's loose).

Here, I think you can change down to a smaller CP to get the swings you want, and tighten down the butt plate so it grabs the CP solidly.

But I don't know for sure about this action...

--Cy--

When you tighten the screws, there is a tendency for the butt plate to sometimes rotate clockwise, causing the plate to contact the inside of the flange. This can certainly add friction and might explain what's going on here.

Make sure that the plate stays at a 90 degree angle to the center pin when you tighten the screw. Let us know if that works for you.

Tom

After posting my reply, I realize that I have the mechanics all wrong in my analysis. The plate does indeed touch the flange, but I don't think that's what causes the friction.

Having said all that, I do know that I've experienced the same problem you wrote about and that when I straightened up the butt plate, the friction went away.

Sorry for the confusion.

Note to self - never post during happy hour :-)

Tom

You would think makers would have learned from the old brass flanges, that butt plates are not the best, especially when they are accompanied by the spring and cord which lasts 20-30 years before breaking. They build em this way because fitting only the bushing to the pin is faster and cheaper than fitting the pin to the birds eye, then fitting the bushing to the pin. Got to save a few pennies per piano...... way to go, makers!

Put the pin in a pin vise and get the correct swings then mount it to the plate.
This will also allow you to feel each bushing so that both sides fit the same.
As suggested you can start with the smallest size.

Thanks for the ideas everybody. I havn't had the time to get back to the flanges yet to try your ideas but I'll write back to let you know how it goes.

Jordan

Ah, yes the butt plate is a worthless system. Ah well, I did find that the hammers will still wobble a bit until you use a big enough pin to keep the plate paralell with the butt and not diagonal. Thanks for the ideas