Yes, go-bar decks are the /sine qua non/ of the harpsichord maker but 
the initial question was "how long" should go-bars be. Well, a little 
longer than the distance between the upper deck and the matter to be 
clamped is a simplistic answer. The originator of this thread appears to 
have a deck with a fixed distance between the upper and lower surfaces. 
If one is going to have to clamp materials of varying thicknesses, one 
must have sets  of go-bars of different lengths to accommodate the 
different distances between the materials to be clamped and the upper 
deck. As the distances grow shorter, the go-bars must become thinner or 
the pressure will rise accordingly. Given the fixed distance (38" as I 
recall) the only way to determine the length/thickness of the go-bars is 
by experiment.

I agree with Michael Johnson that ash is the best material for use as 
go-bars. He has broken three; I have broken one and that was because I 
was too lazy to move my lower deck down and over-bent a go-bar. Ash also 
retains its springiness over multiple uses without losing any of the 
pressure it applies. I do take care to "reverse the curve" if a go-bar 
seems a bit bowed, bending it the other way next time it is used. 
However, between uses they straighten out almost completely.

Just as an aside, I cannot imagine having a go-bar deck which is not 
adjustable to increase or decrease the distance between upper and lower 
surfaces. The notion of having multiple sets of go-bars seems a great 
deal more complicated than being able to move a deck up or down. 
Adjustment methods need not be expensive or exotically engineered. I 
would love to have a set of scissor jacks with which to crank my lower 
deck up and down but I get along with a set of four shim sizes of 2"x6" 
pine to move the deck to preset positions. Since I build pretty much the 
same instrument (Italian 17th Century) repeatedly, this works for me. If 
I built all sorts of stuff, I'd invest in the scissor jacks.

Rob

-- 
ROBERT BROOKE HARPSICHORDS
4214 18th Ave W
Bradenton, FL 34205

www.robertbrookeharpsichords.com

941-746-6725


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