[pianotech] Hammer Cant Angle, was D Hammers

[David Ilvedson]

Pris Rappaport has given many classes on hammer hanging factory style and this is exactly a factory procedure.   European factorys.   But every photo we've seen of factory workers (old time photos) show the worker with the alcohol lamp on the piano as he went through and burned in the hammers.   She even put traveling paper on a few flanges in the hammer hanging jig we were using to show the burning in that will fix all of these traveling problems.   

David Ilvedson, RPT
Pacifica, CA  94044

----- Original message ----------------------------------------
From: "George F Emerson" <pianoguru at cox.net>
To: pianotech at ptg.org
Received: 4/22/2010 10:28:25 PM
Subject: Re: [pianotech] Hammer Cant Angle, was  D Hammers


>----- Original Message ----- 
>From: "David Ilvedson" <ilvey at sbcglobal.net>
>To: <pianoguru at cox.net>
>Sent: Wednesday, April 21, 2010 1:16 PM
>Subject: Re: [pianotech] D Hammers

>>The first thing we did was checking traveling of the shanks and made a few 
>>adjustments then it was
>>checking hammer movement between neighbors as you are talking about.

>Sounds like the same thing by a different means.  I would still what to know 
>if the piano I was working on was originally set up with a strike point 
>scale different from the action scale.  You can determine this as I 
>previously described with measurements at the bass-tenor break.  I would 
>have some concern about adding this clearance cant on a piano that was not 
>designed and built for it.  It would result in having to rotate hammer 
>flanges to center on the strings, bend the backcheck wires left to right, 
>and compromising wippen alignment.

>>We burned in by heating with an electric heat gun and bending towards the 
>>direction the hammer was
>>moving...which seemed counter-intuitive but worked... '-]

>Yes, it works, but all of the hammers in the section have to have the cant 
>for it to work.  It's pretty much the same throughout the bass, gradually 
>changing through the tenor, and none in the treble sections.

>>The hammers all had the cant you are describing.   So with this hammer cant 
>>the hammers do come up
>>to "about" level with the strings..right?

>Not exactly level, but the gang sanding you described pretty much takes care 
>of it.

>>> In the factory, we have a fixture that holds the hammer
>>>molding where the shank engages it, at the spacing of the "action scale,"
>>>but also holds the crown of the hammers at the spacing of the "strike
>>>scale."   This predetermines a slight mounting angle in the bass and 
>>>tenor,
>>>and perfectly vertical in the treble sections.
>>PLEASE describe more...diagram/photo or whatever if this jig.

>It's not something that would be useful in the field, since it requires 
>interchangeable components, specific to each make and model.  Imagine two 
>giant combs, one to secure each hammer where  it engages the shank, and the 
>other to secure the hammers near the crown.  The hammers are held above the 
>fixture for gluing, then rotated down into the two slots, between the teeth 
>of the combs, for drying.

>>I'm still having a hard time understanding the Physics of the phenomenon. 
>>This has nothing to do shank
>>traveling but with the angle of the hammers in the bass and tenor.

>David, your questions caused me to rethink some of what I said earlier. 
>While it is true that the hammer, at the point of engagement with the shank 
>move toward the rear as it moves upward, that does not fully account for the 
>clearance problem.  I modified my grand action 3-D computer model to 
>illustrate and to do some motion studies.  I have saved some JPG files from 
>the CAD software.  I could have saved the motion studies in video format. 
>It is fun to watch in dynamic motion, but that would be too much band width 
>for the list.  In a computer model there is cleaner definition of the shape 
>of the felt, and there are not variations in hammer pinning, etc.  With CAD 
>software, it's easier to rule out possibilities, and to be less likely to 
>wrongly attribute what you see to something else.

>(See: No Cant All Up Back 15 View.jpg)
>The hammers are all mount perfectly perpendicular to their shanks.    Each 
>hammer is identical, as they are all brought into the assembly from the same 
>subassembly model.    This view is at a 15° angle from the back looking 
>straight down the hammers.  You can see they are evenly spaced, at the same 
>bore angle, and perpendicular to the shanks with no cant angle.


>(See: No Cant 2Up Back 15 View.jpg)
>The outside hammers appear to be mounted at a cant, while the center hammer 
>appears not to be canted.  The outside hammers appear to be at an angle, 
>because they are, not because of the way they are mounted on the shank, but 
>because they are rotated downward on the hammer center, compounding the 
>angle of the hammer's centerline.  The hammer is tilted on one axis by its 
>bore, and once again on another axis by rotating downward on its center.

>(See: No Cant 2Up Top 15 View.jpg)
> The angle difference is even clearer from a top view.  Looking straight 
>down, you cannot see the sides of the raised hammer, but you clearly see one 
>side of each outside hammers, at rest.

>(See: Cant 2Up Back 15 View.jpg)
>These hammers are canted at 2°.  You can still see the differences in the 
>angles, but they are less severe on the outside hammers.  The spacing where 
>the hammers come closest is slightly greater.


>(See: Cant 2Up Top View.jpg)
>>From the top, you can see that the angles of the outside hammers are less 
>severe, but there is an angle in the opposite direct of the raised hammer in 
>the center.  The discrepancy in the angles is fairly evenly shared by the 
>raised vs. lowered hammers.  It is hard to see from these images, but the 
>computer measures about 3mm more clearance with the cant, than without it. 
>I had expected more, but that is significant, especially in a tightly spaced 
>action.  Tapering the tails would help too, but that was not a component of 
>this study.

>Thanks, David, for prompting me to add to my body of knowledge and 
>understanding.

>Frank Emerson

>P.S.  Sorry, David.  I did not realize until I started to send this email 
>that I was replying to an email you sent directly to me, rather than the 
>list.  I hope you do not mind my sharing it on list.