Soundboard to Rim Clamping Pressure

[Farrell]

Awesome information Ron. Thanks. It had occurred to me to drill a hole in the top of the wooden handle of the F-clamps I will use and epoxy in a tuning pin. Then I could use my inch-pound tuning pin torque wrench to measure. One could check the estimate of clamp efficiency by clamping on a scale and measuring how much pressure is generated by how much turning torque. Alternatively, if using a bar clamp that bends a little bit under pressure, one could simply calibrate the clamping force as measured on a clamped scale by the bar bend (for any given length of bar).

OK, so now we can measure clamping pressure. Now just to come up with the "right" target clamping pressure. The info did make quite clear why the ranges of suggested clamping pressure. I wonder where the typical board to rim bevel status would fall - are they relatively well machined and mated, or are they not well mated? I should think that if the rim bevel is nice and clean, and you know the spruce will bend easy, that it would fall into the well-mated category. Yes?

Terry Farrell
  
----- Original Message ----- 
From: "Ron Nossaman" <RNossaman@cox.net>
To: "Pianotech" <pianotech@ptg.org>
Sent: Wednesday, September 11, 2002 4:43 PM
Subject: Re: Soundboard to Rim Clamping Pressure


> 
> >I have read a fair bit from various sources regarding the importance of 
> >proper rib-to-panel clamping pressure. Most recommendations range from 40 
> >psi to 100 psi. Other recommendations for softwood glue joints from 
> >woodworking sources (like Franklin) suggest softwoods require closer to 
> >100 to 150 psi. Franklin also recommends higher pressures for hardwood 
> >joints. OK.
> >
> >I have not come across any definitive recommendations for 
> >soundboard-to-rim clamping pressure, save for "not too little and not too 
> >much - go for good squeeze-out". This seems a bit nebulous to me. Anyone 
> >able to be more specific? Perhaps more pressure is required as we have a 
> >hardwood-to-softwood joint there. I would hate to see one of my boards pop 
> >out after a few years.
> >
> >Thanks.
> >
> >Terry Farrell
> 
> Use an adequate amount of glue. Clamp the joint together until it gets 
> solid. Don't crush the piano with the clamps. Mop up before the glue dries. 
> Come back tomorrow and put the clamps away. Sure, it's scary, but trust 
> what you know and pay attention, and it will be fine. If that doesn't get 
> it for you, go here http://www.ukuleles.com/Technology/bridgeglue.html and 
> learn how to produce the exact clamping pressure you want with any kind of 
> screw clamp you may have. Just don't get so wrapped up in the minutiae that 
> you forget the basic design.
> 
> Ron N
> 
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