Juergen wrote: Very intersting topic!
But what is the target of pressure you want for the different tasks using the go bar deck? Are 3 lbs or 1,36 kg enough pressure for glueing the braces and top and back?
Juergen
I just noticed this post - my apologies for the late response.
There are two considerations here - achieving adequate glue line pressure at any point along the brace-to-plate joint and making sure the applied force is evenly-distributed along that joint.
For a well-made joint, adequate glue line pressure becomes more about thinning the glue line down to (for Titebond or HHG) under 0.001"/0.025mm. If the joint is not all that well made, then generating the sort of glue line pressure that is recommended by the glue manufacturer becomes more important. In general, the joint area may be found by multiplying contact patch length x width. From there, determine the minimum number of go-bars necessary to generate the clamping force per unit of area, and then distribute them along the brace as needed to get a uniform glue line pressure.
Note: From here on in, I will use inch (length) and pound (force) units, trusting that the reader will convert that to mm/cm/m, newton/kg(f), and pascals as necessary. I need another cup of coffee before attempting more unit conversions.
An example of this would be a tone bar of 9" length and 1/4" width, giving a joint area of 9" x 0.25", or 2.25 square inches. For a well made joint with hot hide glue, a target clamping pressure of 25 lbs/square inch (a pressure that has been shown to effectively close HHG joints) suggests that the minimum number of go-bars needed would generate an aggregate clamping force of about 57 lbs. For the go-bars I use in the shop, which generate about 7 lbs each, I would need 9 go-bars. For your 3 lb go-bars, we would need closer to 19 to get to that desired glue line pressure of 25 psi.
The other issue is achieving uniform clamping pressure. A conservative assumption here is that an applied clamping force only affects a relatively small area of the joint, with the force from a go-bar propagating through the material at 45 degrees around the line of application. We want this force to slightly overlap with that generated by other go-bars, so - for a 0.5" height brace - we would need to space the bars within 1/2" of each brace end and no more than 1" between each bar. For that 9" long tone bar, I would need a minimum of 9 go-bars to provide even clamping pressure, and that generates my target clamping force as well using my 3/16" x 24" bars. For your 3 lb clamping pressure go-bars, those 19 required bars would be spaced at just under 1/2" between bars and 1/4" at the ends, so the clamping pressure would be very uniform.
|
)
You've got to be kidding. Isn't there enough to worry about building guitars? Formulas for go-bar rods 
I can't get involved in this one. Yet, here I am.
