Making bridges

Ron Overs sec@overspianos.com.au
Fri, 9 May 2003 09:04:47 +1000


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>Ah, Ron, we can tell you're not a wooden boat builder!

That's right, strictly pianos in my case.

>A good scarf joint will equal the strength of a solid wood beam. And 
>it will have a slope of 1:8 (non-structural use) or 1:12 (structural 
>use). 

Sure, but no one has to my knowledge built pianos bridges with such 
low scarf angles, since there would be a greater wastage of wood with 
a lower angle and it is not required from a structural perspective. 
While I was aware joint strength increases relative to the scarf 
angle, I felt it appropriate for the sake of brevity not to write a 
thesis on the matter. My apologies if you felt I didn't address the 
issue adequately. I mentioned the 1:5 joint as typical because that's 
what it is typically used in piano bridges.

>The amount of slope also varies with the glueability of the wood 
>being joined. Spruce bonds very easily, maple somewhat less so. 
>Finger-joints, by the way, are simply a form of scarf-joint. In this 
>case the scarfs are made short and are stacked for less wood waste.
>
>We can compromise on the slope of the scarf in the construction of 
>piano bridges because it is a "non-structural" application. The 
>absolute beam strength is not critical.

Thank you.

>  Del

Ron O.

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