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#644375 - 04/25/04 03:44 PM Action Geometry Question
JazzManToo Offline
Full Member

Registered: 04/25/04
Posts: 104
Loc: Somerville, Massachusetts
Hello All,

I've been lurking here for awhile and have learned many things while doing so. I'm DIY tuner and have been learning to regulate and repair my own pianos. I really enjoy it. I've re-read Reblitz's book and have read everything I can find on the geometry of piano action but I'm still confused about something regarding my '68 Baldwin L.

It believe that when the a hammer hits its strings, the shaft should be perpendicular to the strings. So the distance from the tip of the hammer to the center of the bore should be equal to the string height above the keybed minus the flange height above the keybed plus half the diameter of the shaft. But, on my L the distance to the bore is greater then this. This means the strike point on the hammer is a little forward of the center of the hammer. This is also evidenced by the grooves in the hammers. I purchased the piano used and have no history, but it's my impression that these are not the original hammers. Now here's the thing that's bothering me: When I first regulated the action, I found that the hammer blow distance was 2 inches. Not the 1.75 inches recommended by Reblitz. I regulated them to 1.8 inches, but then when regulating letoff, on several notes, I had to go right to the end of the adjustment range of the letoff button. Now given that my hammers are longer then what they should be (I think), how would I adjust letoff with a shorter bore distance and higher hammershaft height? Or which part of the geometry am I wrong about?

Love that #11!

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#644376 - 04/25/04 07:51 PM Re: Action Geometry Question
TomtheTuner Offline
500 Post Club Member

Registered: 07/29/01
Posts: 806
Loc: Melbourne, Florida USA
Make the hammer blow distance 2" . So long as the letoff, dip and aftertouch are even and workable then you will be ok. You probably will want to replace the hammers with the proper size sometime in the future. But I think you have diagonosed the problem quite well.
Maker of the TCHAMMER


#644377 - 04/25/04 09:40 PM Re: Action Geometry Question
BDB Offline
Yikes! 10000 Post Club Member

Registered: 06/07/03
Posts: 22283
Loc: Oakland
Specs for hammer blow on a Baldwin is 1-7/8".
Semipro Tech

#644378 - 04/25/04 10:12 PM Re: Action Geometry Question
JazzManToo Offline
Full Member

Registered: 04/25/04
Posts: 104
Loc: Somerville, Massachusetts
Thanks for the info. I'm getting less confused. Everything is working fine with the hammer blow distance set to 1.8 inches. And I was able to get the letoff to 1/16". But I'm pretty much at the limit on some of the letoff buttons, which puts me at the limit of hammer blow. And the confusion I was having is that if the boring distance on the hammer were shorter, I'd have to raise the hammers even more and I'd be out of adjustment range at the letoff button. In any case, since starting this thread, I've looked at a grand action cross section again and I think I understand what might be the problem. It looks like any small wear or compression of the knuckle would have a big effect at the hammer end of the shaft. So I'm guessing worn knuckles are a part of the adjustment limit problem.

But I am correct about hammer bore length? The hammer shaft should be just about parallel with the strings when the hammer strikes?

Thanks again.
Love that #11!

#644379 - 04/25/04 11:36 PM Re: Action Geometry Question
curry Offline
3000 Post Club Member

Registered: 08/17/02
Posts: 3770
Loc: Hamilton Twp, NJ
Jazzman,worn knuckles would play a big role in not being able to set a close let-off. Also take into consideration how much felt has been taken off the hammer by reshaping. This can also cause what you're describing. The Baldwin spec is 1 7/8" for hammer blow,1/16" for let-off and drop,and 13/32" for keydip. Are the keys leveled at the correct height? The Baldwin spec is 2 1/2".Try getting close to these numbers,you will see better results.
G.Fiore "aka-Curry". Tuner-Technician serving the central NJ, S.E. PA area. b214cm@aol.com Concert tuning, Regulation-voicing specialist.
Dampp-Chaser installations, piano appraisals. PTG S.Jersey Chapter 080.
Bösendorfer 214 # 47,299 214-358

#644380 - 04/25/04 11:50 PM Re: Action Geometry Question
BDB Offline
Yikes! 10000 Post Club Member

Registered: 06/07/03
Posts: 22283
Loc: Oakland
The hammer should be perpendicular to the string. If the hammer is bored to 90°, then the shank should be parallel to the string. However, all of this is pretty difficult to measure. It depends on a lot of things. It also varies as the hammers wear and are reshaped.

The standard boring length for Baldwin hammers is 1-7/8" in the treble. The let-off is not dependent on the hammer blow, although if the blow is far off, the hammer may not let off at all. As the hammers or knuckles wear, you have to raise the let-off, and eventually you could reach the upper limit of the buttons, provided the let-off rail was correct in the first place.
Semipro Tech

#644381 - 04/26/04 12:46 AM Re: Action Geometry Question
JazzManToo Offline
Full Member

Registered: 04/25/04
Posts: 104
Loc: Somerville, Massachusetts
Thanks for all the Baldwin specs and other info. The keys are leveled correctly. Key dip is 3/8". Next time I'll try 13/32". The overall regulation seems very good right now. Plays just fine with good repetition But I guess new or bolstered knuckles will be required next time I have to regulate letoff.

Thanks again.
Love that #11!

#644382 - 04/26/04 01:00 AM Re: Action Geometry Question
BDB Offline
Yikes! 10000 Post Club Member

Registered: 06/07/03
Posts: 22283
Loc: Oakland
You might want to see if Baldwin will send you a service manual. Theirs has been quite good.
Semipro Tech

#644383 - 04/26/04 02:44 AM Re: Action Geometry Question
Rick Clark Offline
1000 Post Club Member

Registered: 01/04/03
Posts: 1810
Loc: North County San Diego CA
Not all pianos are designed for the shanks to be parallel and the heads to be 90 degrees, but I think most American pianos are. However one must always deal with the individual piano one has, and not be too surprised when one finds something different than the norm. Some companies have put out highly variable product. One will also find a great number of piano actions that were built with less than ideal geometry. Don't assume that "big name" piano companies always strive for excellence. Some can be quite sloppy sometimes.

When the hammers are replaced any number of things can go wrong to screw up the strike if the tech doing the work does not grasp the concepts. I've seen far more bad hammer replacement jobs than good ones, and I suspect yours is a bad one too. Anything less than an excellent precision hanging jig and complete knowledge of what is involved in precision hammer work will usually result in junky hammer hanging.


Rick Clark
Rick Clark

Piano tuner-technician


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