[CAUT] moving capstans question

[Paul T Williams]

Hi again all.  Well, the piano is being used this afternoon, so Monday 
I'll get in there and look at everything again.

Good hints from everyone.  Thank you! I meant to say move the caps forward 
(toward me) not back! :>O 

Other things I didn't check at last glance was size of the leads, wear 
(cupping) on the cuhions, or knuckle to flange center measurements.  My 
bad!  To get a better idea of the age of the parts, when did Renner start 
using rep spring screw?  Or did they always have it?  They look so new I 
have to wonder if they had been replaced at one time. The more precise 
year for the piano is 1979...

I'll report to all on Monday!

Enjoy.

PW





Fred Sturm <fssturm at unm.edu> 
Sent by: caut-bounces at ptg.org
09/21/2007 12:27 PM
Please respond to
College and University Technicians <caut at ptg.org>


To
College and University Technicians <caut at ptg.org>
cc

Subject
Re: [CAUT] moving capstans question






Hi Paul,
What you are describing is a convergence issue, rather than a leverage 
issue (though there may be leverage issues as well). The line from balance 
hole bottom to wipp center is the "line of convergence" and you want the 
top of the capstan/bottom of the wipp to be on the line when the key is 
halfway through a keystroke. This mostly affects friction, how much the 
capstan and wipp cushion felt rub back and forth against each other. The 
least amount will occur when you have it set up as I described. It usually 
doesn't have that much of a noticeable affect on touch unless the capstans 
and wipp cushions are "gunked up." It will affect wear, how long the 
cushion felt lasts and how soon it becomes badly cupped.
If this is enough of a problem to address, the best way to address it is 
with wipp heel changes. For what you describe, you want a thinner wipp 
heel. Picture it like this: hold everything in place, and shave X amount 
off the bottom of the wipp heel. You will now have to raise the capstan to 
meet it. Hence, the contact between capstan and wipp cushion will be 
higher relative to the line of convergence.
Moving the capstan line will affect convergence, but only "by the way." 
Let's be clear what we mean by back and forward: back, toward the back of 
the key, forward toward the front of the key and the player. Moving back 
will make the capstan lower relative to the line of convergence. Moving it 
forward will make it higher. (The line of convergence is slanted relative 
to the top of the key). But the main effect is on leverage. Moving the 
capstan back means higher ratio, and heavier touch (all other things being 
equal), and means less keydip for the same blow. Moving forward does the 
opposite: lower ratio, lighter touch, and more keydip for the same blow.
Raising or lowering the stack has a lot of side effects, especially having 
to do with hammer bore distance and how squarely the hammer hits the 
string. You don't want to go there unless you are able to think of all the 
effects. Well, raising it is simple to experiment with, just a few shims 
you can easily remove, and not a lot of time lost. And you can consider 
just shimming the back legs, which you can do more of without causing 
problems getting the action assembly in and out under the pinblock. But it 
does have other regulation effects besides just the convergence thing.
I guess I would start by questioning whether convergence is the issue here 
that is making people hate the piano. The most likely problem is new heavy 
hammers on old knuckle geometry (16 mm or so vs. 17 mm or so current 
specs). In that case, best solution is probably moving the knuckles, 
whether that means new shanks with different knuckle placement, or cutting 
new slots on the old and installing new knuckles - which requires 
specialty jigs.
Regards,
Fred Sturm
University of New Mexico
fssturm at unm.edu



On Sep 21, 2007, at 8:34 AM, Paul T Williams wrote:


Hi List! 

Happy Friday! 

I am working on a 70's Sty B with a horrible action geometry problem. All 
the students and the professor hate playing it and I don't blame them! The 
line from key balance hole to wip has the capstan way too low making the 
DW close to 70g throughout.  It has a renner action and hammers.  the wips 
and capstans are such that I could relocate the capstans back by about 
3-4mm.  Would that make a big enough difference in the DW? It won't affect 
the line.  I looked at raising the stack, but there isn't enough room to 
raise it more than 1-2mm.  Should I try both? 

Also, is the measurement in Steinways made from center of balance rail 
hole on the top of the key, or from the back of the key?  This is a new 
endeavor for me and I don't want to make things worse. 

Still green in Lincoln, 

Paul

-------------- next part --------------
An HTML attachment was scrubbed...
URL: https://www.moypiano.com/ptg/caut.php/attachments/20070921/d630e01c/attachment.html