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| Popped Back Brace http://www.luthiersforum.com/forum/viewtopic.php?f=10101&t=22538 |
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| Author: | gullywompr [ Wed May 27, 2009 11:59 pm ] |
| Post subject: | Popped Back Brace |
Greetings all. I'm building my first, a Martin-style dread. After assembling the top and back to the sides, I have begun to work on the bindings. While doing so, I put too much pressure on the back plate and popped the bottom-most (nearest the tail block) brace loose in the center, although it remains glued at the ends. Imagine a yardstick lying on a table, with glue under the one-inch marker, and glue under the 36-inch marker. You can grab it at the 18-inch marker and pull it up from the table slightly, but it remains attached at the ends. This is roughly the case with the back brace in question. I think the problem was when using go-bars in the dish, I must have tilted the brace such that glue contact with the back was only along a corner, rather than along the entire surface. Any ideas on how to get the brace reattached would be greatly appreciated. I can only reach one hand in, and can just reach the brace. I can visualize getting a syringe of glue in there, but I have no clue how I could clamp it back down. I suppose I could try 5-minute epoxy, and endure the cramps while I hold it against the dish. Super-glue seems a little risky - I don't want to go trough the rest of my life with my hand stuck inside a half-finished box, but it might be a risk I could take if there were a good technique for it. Like I say, this is my first, and there are flaws galore. I'm willing to overlook the cosmetic ones and try better next time, but a constant buzz from a loose brace is not something I can accept. Please help this newbie out. |
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| Author: | Carey [ Thu May 28, 2009 1:22 am ] |
| Post subject: | Re: Popped Back Brace |
If the brace popped loose under finger-pressure, I'd wonder if there were other issues also. The first one that comes to mind is humidity control, or its lack... I once started to re-top a guitar, but as soon as the top was removed the back went flat, and the sides spread out quite radically (at the top). This was on a Japanese (albeit handmade) classical guitar, and my understanding is the humidity in the region where the guitar was made is usually high. Was the humidity regulated when the 'box' was assembled? |
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| Author: | Sondre [ Thu May 28, 2009 6:07 am ] |
| Post subject: | Re: Popped Back Brace |
On loose back braces, I use a syringe and these jacks from stew-mac. Works great for me |
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| Author: | bluescreek [ Thu May 28, 2009 6:17 am ] |
| Post subject: | Re: Popped Back Brace |
On loose braces, first what glue did you use ? If you used anything other than hide glue you need to get the old glue out or your new glue job won't hold. Take some sand paper and work it under the loose brace and sand both sides. This should clean you up enough for the wood to stick. To work the new glue into the joint I found paper is as good as it gets. Lay the paper under the brace and drop glue onto the paper and work that back and forth until you smear the glue well into the area of concern , clamp and let dry , you should be fine. For clamps , if you are working in a closed box I use some plastic 4 inch pipe ( white non sch 40 ) and by cutting this from 1/2 inch to 1 inch wide I get different weight push. I will cover the pipe with friction tape , squeeze it in and done. You can also make jam sticks. You only need enought pressure to make wood to wood contact. |
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| Author: | gullywompr [ Thu May 28, 2009 4:04 pm ] |
| Post subject: | Re: Popped Back Brace |
The glue was Titebond. I'll sand it out. John, if I understand, you are cutting "O" shaped slice of pipe, and rolling them in until the circumference starts to apply pressure? That sound nice and easy, and I have some 4" white pipe fittings I could use. Sondre, those brace jacks look perfect. I am going to put some thought into home-making them. (I love stewmac, but I love a challnge even more). Carey, you're right, no humidity control in my basement shop. But it wasn't really finger-pressure, more like elbow-pressure (there's a lesson in itself right there - don't lean on the box when you work). Not particularly humid when glued up, but it has been so for the past week. Thanks to all, this list is an incredible resource. |
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| Author: | woody b [ Thu May 28, 2009 7:34 pm ] |
| Post subject: | Re: Popped Back Brace |
If the brace wouldn't stand "elbow pressure" it would have been a problem sooner or later(probably sooner) without the elbow. I believe keeping the humidity low enough while building is very important but there could have been other factors. |
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