After reading my post, I would like to further clarify some of my statements.
The use of the spring clamps is both the method and the test. It can't be done with the key blocks screwed down as I implied previously.
In the end, the key frame should be bowed/reverse crowned slightly with the ends off the key bed.
With proper bedding the pressure of the spring clamps must be able to exert enough pressure to draw the ends down to the key bed.
With proper bedding the spring clamp on the frame should exert the same down pressure at the ends as there is across the entire key frame.
Once the key frame has been bedded, the key/cheek blocks should be set to exert the same down pressure as did the spring clamps.
<Then we tested it with the key blocks to be sure nothing changed and that it was exactly the same>
To little pressure with the key blocks screwed down, the ends will knock. To much pressure with the key blocks screwed down, the center of the frame will lift and knock.
The point of bedding the frame to the key bed is to have the same pressure across the key frame/ key bed, center to ends. The spring clamp is the gauge. If it can pull down the end and you have the same down pressure across the key frame, you are done. The spring clamp is the proof that it's done and is right.
Al G
From: Al Guecia/AlliedPianoCraft
Sent: Friday, August 14, 2009 8:05 AM
To: pianotech at ptg.org
Subject: Re: [pianotech] Key frame hold downs
One last point. If the spring clamps are not working reliably, that is proof positive that the key frame hasn't been bed properly.
Al G
From: Al Guecia/AlliedPianoCraft
Sent: Friday, August 14, 2009 7:47 AM
To: pianotech at ptg.org
Subject: Re: [pianotech] Key frame hold downs
William, this is my last post on this subject, but I would like to make myself clear.
1, I do not disagree with you that the clamps did not work for you at the factory.
2, I do not disagree with you in that it may not be a reliable method with today's key bedding.
What I am saying is this.
1, I was taught to bed the key frame with equal down pressure across the entire key frame by Fred Dracshe using the spring key clamps. Then we tested it with the key blocks to be sure nothing changed and that it was exactly the same. If you tried to bed a key frame using the key blocks screwed down it would take forever. Once you bed the key frame with that method, they could be used with good results on the bench.
2, I used this method for 11 years at Steinway and 35 years since then with reliable results.
My point is this. If you bed properly with the springs and you test the result with the key blocks. The springs are reliable.
Al G
From: William Monroe
Sent: Thursday, August 13, 2009 8:36 PM
To: pianotech at ptg.org
Subject: Re: [pianotech] Key frame hold downs
I understand the point, and it simply doesn't apply here. How does one get too much reverse crown? Someone would have to be ridiculously aggressive, sanding at the ends of the frame to create such a situation. I'm not suggesting one needs a bench vise to clamp the keyframe ends down satisfactorily. I'm just saying the key frame clamps did not hold the ends of the frame down securely. Kent Webb was somewhat involved in this and agreed that the clamps were not the same as screwing in the cheek blocks. This was done on new instruments at the factory, and while I didn't take the frame out and measure the radius on the keyframe (), I'm pretty confident it was not excessive, nor were the pins bent, nor were there any other anomalies that could be indentified. The end result was simply that the two methods yielded different results.
?? I'm not sure what else I can say. As before, if it works for you, great, full speed ahead. I no longer use them as I don't have confidence in the accuracy of that process.
William R. Monroe
>With the reverse crowned key-frame, you've simply got to have enough force to bring the ends of the frame into contact with the bed>
That's my point William. If you have too much reverse crown or at too sharp an angle at the ends, Yes, it won't work.
Al G
All due respect, but no. In my case, the frame was bedded well. The clamps did not have enough force to bring the ends of the key frame into contact with the key bed. That's just the way it was. With the reverse crowned key-frame, you've simply got to have enough force to bring the ends of the frame into contact with the bed, and the clamps did not work well on the four pianos I tried them on. As I said, YMMV and if you've found them to work for you, great.
FWIW.
William R. Monroe.
William R. Monroe wrote:
However, I personally don't recommend them, at least not for S&S ...... When I was in NY last spring, I tried a little experiment with them, and they did not ACCURATELY replicate the pressure of the cheek blocks - and this really is essential in S&S.
If the key frame is bedded properly, they work great. If need to exert that much pressure with the key blocks, you can be sure the bedding is not right.
Al G
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://ptg.org/pipermail/pianotech.php/attachments/20090814/afcb9359/attachment-0001.htm>
This PTG archive page provided courtesy of Moy Piano Service, LLC