The oldest question in the world:
“What is that thing?”
Yesterday Brian asked a question about my clamping system for bracing the guitar soundboard. I had assumed the details would either be obvious or uninteresting to folks, but the question reminded me (as good questions do) to think back to when I was trying to work out the idea for myself.
The setup is most commonly referred to as a “go-bar” clamping system. As Kieran mentioned yesterday in the comments on the last post it’s an interference system where you basically jam something too big into a space too small and thereby create pressure. Sounds elegant eh?
What you jam isn’t important as long as it’s flexible and resilient (and the right length) and where you jam it isn’t that important as long as it’s sturdy, flat (and the right height).
But as far as I was concerned, those two parenthetical concerns were the main problem and as I was working on getting it set up I found a startling derth of detailed information on the sizes and measurments i would need in the construction of the thing.
The best information I could find was from Stewart Macdonald, which gave me info on the deck itself, but I just felt like it was missing details that I wanted to know before dropping coin on all of the materials.
“How long are the bars?”
“Can I make it a different size?”
“Will it work if I make the bars myself instead of taking out a loan to buy the ones from Stew Mac?”
“How many will I need?”
I didn’t know anyone to ask and the answers I got from the internet were tantamount to “long enough so they work,” “maybe,” “probably, but no garauntee” and “enough.”
Super helpful, Internet. Thanks.
At that point I decided to build the deck pretty much as shown by the Stew Mac plans. I went to the local big box home improvement store and bought a sheet of 1/2″ plywood. I got them to cut it in half long ways so it would fit in my car, but also because it would mean less cutting at home with the circular saw. The rest of the cuts were made at home leaving me with eight 2′ x 2′ squares. I laminated four of them together for the base and 3 for the top, trying to balance rigidity with overall weight.
The uprights are 1/2″ threaded rod sleeved with 3/4″ aluminium pipe. The washers, bolts, etc are all pretty standard.
The whole thing looks like this:
You can see the clamp bars in action here, but they’re pretty basic in construction. I bought 5mm fiberglass rods, cut them down and put rubber tips on the end. I made 24. I wish I had made 34.
Each one produces about 5lbs of pressure.
The effect is cumulative.
That’s good to know because, while you generally try to space them out evenly, you can put several close together if you need more clamping pressure on a certain spot.
It’s also good to remember that when you have all of them installed you’re putting ~ 120lbs of pressure back on the top of the deck. A good reminder not to skimp on the top deck because you don’t want it bending under pressure.
This is just about perfect for bracing a guitar because it gives you a solid glue joint without starving the joint. If you’re careful with the amount of glue you apply, you don’t have a ton of squeeze out and what you do have can easily be cleaned with a glue chisel.
I use these shop made radius dishes as clamping cauls to give proper radius to the top and back. There are different ways to skin this cat. This one made sense to me.
And that’s the long and short of it.
Oh, speaking of long and short, it might help to give you those measurements I searched long and hard for.
The space between decks is 30″. My go-bars are 29.5″
Each of the disks is 3/4″ thick so 1.5″ stacked. I keep them stacked when I’m clamping so essentially I’m jamming a 29.5″ bar into a 28.5″ space which gives me ample pressure but still keeps the bars workable and out of one another’s way.
I’m happy to fill in any details I may have omitted. I know how frustrating that can be.