Bridge cap materials

[Farrell]

Sounds very interesting. Thank you for the explanation. Let me restate my understanding just to be sure. You take a quarter-sawn hunk of bridge cap material from either the supply house or a lumber yard and resaw it on a plane parallel with the soundboard (you know what I mean - the way the cap wood would be sitting on the bridge/board). Then you basically re-assemble the same piece of wood only skewing the laminations on 10° angles. So you end up with your same piece of quarter-sawn maple only now you have the grain crossing at 10° angles from layer to layer (I hope that makes sense).

Can I assume that with this process you end up with a lot of wasted wood? How do you clamp your laminations? I should think the assembly would be too wide for your pneumatic clamps. Do you just use a whole bunch of clamps closely spaced?

Then you mention rotary cut maple. Now how would you go about making a high quality cap out of that?

Terry Farrell
  
----- Original Message ----- 
From: "Ron Nossaman" <RNossaman@cox.net>
To: "Pianotech" <pianotech@ptg.org>
Sent: Saturday, October 12, 2002 11:58 AM
Subject: Re: Bridge cap materials

> >How does laminating maple at whatever angle affect its hardness - i.e. how 
> >is this better than solid quarter sawn stock?
> >
> >Terry Farrell
> 
> Hardness wasn't exactly the right word, but it was the quick one. 
> Resistance to compression is more what I had in mind. With quarter sawn 
> stock, the spacing of the annular rings will have a lot to do with it's 
> compressibility. As Dale noted, driving pins in a wide grained cap requires 
> a smaller hole than in a close grained cap for the same tightness. The wide 
> grain is more easily compressed. In quarter sawn stock, the rings are 
> parallel. Drive a pin in and wood of only a couple of rings is affected by 
> any one pin. Wood a couple of rings on either side will compress to 
> equalize the forces, taking away from that tight fit around the pin. The 
> wider the grain, the farther from the pin that compression equalization 
> spreads, and the less tight the pin will be for any given hole.
> 
> Laminating, even at a low cross ply angle, has the effect of increasing the 
> average density of annular rings for any given pin hole. Hard late wood 
> rings are locked one to the other in successive laminations. The rings 
> aren't parallel the length of the pin, so the compression gradients around 
> the pin in any given layer will be steeper, and won't extend out into the 
> surrounding wood as far. Even with flat sawn or rotary cut laminations, 
> this will be a factor, as well as the change in direction of the long grain 
> every lamination that should eliminate any tendency toward splitting. Each 
> lamination also soaked up a little glue during assembly, and is a bit less 
> compressible for that reason as well. You'll have a hard time driving a #7 
> (0.086") pin into a 0.81" hole like you would do with little problem in a 
> quarter sawn cap.
> 
> These caps also don't change thickness with humidity swings as much as a 
> solid cap (at least by my tests), so I'm anticipating they should age more 
> gracefully and produce fewer false beats through the years. But that 
> remains to be seen.
> 
> So far, I like it.

> 
> >         How are you milling maple that thin?
> >         Dale
> 
> The time consuming hard way, re-saw and thickness planer. If I was running 
> a high volume operation or building pianos, I'd just buy a load of rotary 
> cut maple and save a lot of time. I'd make my own pinblocks too, since I'd 
> have all that nice maple lying around not being used up fast enough in 
> bridges and caps. So for now, if I want to use a nice laminated cap that I 
> can hand notch, I'm stuck with the milling.
> 

> 
> Ron N
> 


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