#1
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Springback - What is acceptable?
As per the title I am getting to the stage where the back is ready to be installed to the rims. I notice that when I free the ribs from the mold there is a certain degree of springback, it doesn't seem to be a serious issue, as it gets back into it the mold with only a slight degree of persuasion.
How much springback is acceptable and won't cause any structural issues due to the stress of holding it in shape when the back/top is attached? I know ideally no springback is the goal, but the tailblock, neckblock, side reinforcements are already all done. Should I go ahead and use the mold to get it into shape and simply glue up? or is there a better approach to take. Thanks in advance. Nahil. |
#2
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Quote:
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#3
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Thanks Charles!
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#4
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I've always had it in my head ever since I started building that spring back forced into a mold causes unwanted stresses on the top when the guitar is released from the mold.
It's probably nothing but hey, this is the Internet so I thought I would throw a wrench in it In fact it's one of the reasons I have adopted the 'build off the top' model. But even building off the top sometimes you force into position the sides a bit to make them conform to the lines. So I think it's a valid question. What amount of force is acceptable? I think I remember in Cumpiano's book, who builds off the top, suggested that 1/8th of an inch away from the line is acceptable. That's not an amount of force but it gives you an idea. |
#5
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Really depends. The back and top each will take some stress from the sides. This makes the back and top a little tighter than if no stress were applied from the sides. So if you have a little more 'pull' from the sides making the top or back more 'stiffer' then the top or back can be a little more thinner for the same stiffness. Or you can have the sides impart no load on the top or back and have the top and back a little thicker to retain more stiffness.
Or I may have it wrong. But either way a good guitar can be made. As said, a guitar is just a number of variables, how you juggle them will make the guitar sound as it does. I bend the sides to get close to the shape I want then build it without a mold. As long as it can fit in a case I am happy.
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Fred |
#6
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A thought
I found for myself that using reversed kerfing while the rim was in the mold went a long way in maintaining rim shape out of the mold. I install kerfing when the rim is firmly fitted to the mold, the spreaders making sure of the shape. I'm happy when the rim is square to the mold and the spreaders allow no motion. Springback is no longer a factor, or evident.
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#7
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If I have to pull in the neck and tail block area of the sides by 3/4" to 1" as they go into the sides before any glue up at all, I'm fine with that. As soon as I install the neck and tail block, the sides don't move at all, slide in and out of the mold just fine. but I might still use interior push-sticks to force the sides out at the waist area, or around the lower bout. As soon as I install the kerfing, the sides are rigid(ish), they really take the shape firmly and are quite hard to move. There is no residual force on the top or back at all from the sides, as far as I can see.
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Brian Evans Around 15 archtops, electrics, resonators, a lap steel, a uke, a mandolin, some I made, some I bought, some kinda showed up and wouldn't leave. Tatamagouche Nova Scotia. |