Bridge cap materials

[Ron Nossaman]

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>I see clearly the reasoning behind an advantage to skewing laminations of 
>quarter-sawn maple for a cap. I understand how you can laminate rotary or 
>flat sawn maple into a cap, but I don't understand why it would make for a 
>good cap. Won't you end up with something that is essentially a flat-sawn cap?

No, because of both the cross ply and the glue.


>  I guess I don't know too much about why it is said that a quarter sawn 
> cap is better than a flat sawn cap - I guess I just assume that 
> experience has shown that the quarter sawn is stronger - more resistant 
> to crushing by the string.

I didn't say, but the flat sawn caps tend to split easier. They also tend 
to be softer, or at least to "act" softer, I think, because the same 
horizontal compressibility I described from inserting the pin in wide grain 
quarter sawn wood is there in the vertical direction in the same wide grain 
wood that's flat sawn. Wood is generally more compressible radially than 
tangentially. The difference in solid and laminated is in the laminations. 
The glue and the crossing of late wood grain lines shores the thing up and 
makes it less compressible than solid wood of the same grain density.



>  If you are using rotary cut or flat sawn laminations, does this work 
> because the glue makes the wood stronger overall? It's easy for me to 
> imagine that flat/rotary sawn maple would hold a pin better (because the 
> pins would be going through multiple layers of the more dense dry season 
> or late summer wood - which would be the case whether it is laminated or 
> if it is flat sawn).

It doesn't work that way in solid flat sawn because the direction of 
greatest dimensional change in wood with a change in MC is tangential. Pin 
tightness changes more with flat sawn cap than quarter sawn - in solid 
wood. Laminated, both the glue impregnation and the cross plying counter 
this somewhat. Enough that I don't consider it to be a problem.


>What about carbon fiber - or some other nice hard plastic? Isn't there a 
>nice homogeneous non-biotic material that has all the right properties of 
>hardness, glueability, cutability, etc.? (Kinda fun making up your own words!)
>
>Terry Farrell

Sure, why not? Why have bridge pins at all, for that matter? Until then, I 
can make what I think is a better cap with the materials and technology 
available to me now. Tomorrow is another story.

Ron N

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