rockinrobert Posted December 3, 2003 Report Share Posted December 3, 2003 OK gents here is an idea for my first project. I have an old Alvarez 12 string acoustic that I haven't played since the 80's because the top started bulging below the bridge and even after I had my luthier shave the bridge down, the action became too high and I stuck it in the closet. After finding this website, I have been itching to have a project to begin. This guitar is useless as is, so it could be my ideal first project, if I scrap it, no big loss. My question is this, should I try to fix the top as-is, or should I attempt to re-top this thing? There are no cracks or visible anomalies in the top (at least from the outside). I realize re-topping is a big step, so what do you guys do for bulging tops, especially on 12 strings? My luthier said he had ways of correcting the top but wouldn't divulge his secrets. So now I am asking you guys for your secrets and advice I have some pics of this thing I could post if anybody wanted to see it. I will attempt to stick the camera inside to see if I can get a shot of the bracing and maybe spy anything awry there. Thanks for any advice you can give me. bOb Quote Link to comment Share on other sites More sharing options...
Brian Posted December 3, 2003 Report Share Posted December 3, 2003 Sounds like the bracing migth end up being the problem to begin with or lack there of if the top has seperated from it. Replacing the top with something new and exotic or repairing the pre-exsisting one really depends on what you fell like doing to it though well that and your wallet, some woods can get expensive plus cutting to the exact dimetions of the previous top can be something to ponder about. LGM has more experience on building Acoustic guitars then I so maybe he will see this and shead some light on the subject. Quote Link to comment Share on other sites More sharing options...
Setch Posted December 3, 2003 Report Share Posted December 3, 2003 Shaving the saddle is a short term mod which rarely helps, since it doesn't address what caused the fault in the first place. The cause are commonly failed bracing/bridgeplate etc causing the top to distort excessively, or the guitar simply 'settling in' to a new shape which balances out the tensions acting on it. If the first is the case, you need to locate the fault, rebrace/replace the bridge patch and clamp the top to a flat surface whilst gluing up. This should remove the belly, and repair the structural member so it can't happen again. If it's the latter, you need to reset the neck. Eitherway, I'd be suspicious of a tech who won't reveal his techniques to you (it's your guitar, you have a right to know what he plans!) and wary of one who 'fixies' this kind of problem with a shaved saddle. It's possible he's just working in a fashion appropriate to an inexpensive instrument, but it's equally possible that he's a hack. Quote Link to comment Share on other sites More sharing options...
Southpa Posted December 4, 2003 Report Share Posted December 4, 2003 I recently repaired an acoustic (6 string) that had similar problems. The bracing inside was at fault which caused the area forward of the bridge to sink which, in turn, caused the rear of the bridge to pull out. Feel around inside for any bracing pieces that have separated from the top or any that might have split. In my case MOST of the bracing pieces had problems (some split and some separated). However, they were still in position. This fix was a BIG pain in the ass because all the glueing, clamping etc. had to be done thru the soundhole. You'll have to figure out various ways of clamping and will find yourself using a variety of different clamp types. Clamps with long jaws that can reach rear bracing pieces come in real handy. I also precut pieces of 2X4 and wedged them inside to hold pieces against the top after glueing. I applied yellow carpenter's glue with a medium sized syringe between bracing pieces and the top. Worked very well! Then clamp the piece down any which way you can. I also beefed up the bridge mounting. Most acoustic bridges are glued AND bolted down. For repairs like this I usually glue a strong piece of wood (< 1/4" thickness) to the underside of the top directly under the bridge mounting. Then drill thru from the top to complete the mounting screw holes and the holes for string hold-down pins. When bolting the bridge down I also like to use flat washers to evenly displace pressure when tightening. When glueing the bridge down I score the guitar top and the mounting surface of the bridge with 80 grit sandpaper. A good rough surface retains glue and makes a much better foundation. Be sure you put masking tape around the perimeter of the bridge patch on the top to prevent any damage to the surrounding finish. Quote Link to comment Share on other sites More sharing options...
Setch Posted December 4, 2003 Report Share Posted December 4, 2003 I also beefed up the bridge mounting. Most acoustic bridges are glued AND bolted down. For repairs like this I usually glue a strong piece of wood (< 1/4" thickness) to the underside of the top directly under the bridge mounting. Then drill thru from the top to complete the mounting screw holes and the holes for string hold-down pins. When bolting the bridge down I also like to use flat washers to evenly displace pressure when tightening. Do you mean you use bolts for gluing the bridge down, or leave them in permenently? If you leave them in you will compromise the tone immeasureably by adding that much mass to the bridge. A single bolt probably weighs as much as an entire bridge, by botling your bridge down you're adding triple the weight, and this *really* inhibits the movement of the top. AFAIK only Gibson have ever used bolted on bridges, and every repair person I've heard agrees that removing the bolts and just glueing the bridge is the best favour you can do for these guitars! See what Franks Ford has to say about it... When glueing the bridge down I score the guitar top and the mounting surface of the bridge with 80 grit sandpaper. A good rough surface retains glue and makes a much better foundation. Be sure you put masking tape around the perimeter of the bridge patch on the top to prevent any damage to the surrounding finish. Modern day myth. Scoring is not only unhelpful to a good glue joint, it actually weakens the joint. I've gone into this in depth before, so won't go too scientific, suffice to say, perfectly smooth, mated surfaces produce the best (read -strongest and least visible) glue joints with aliphatic or hide glues. Scoring was common practice at Martin guitars (amoungst others) but is no longer used because so many bridges popped. Quote Link to comment Share on other sites More sharing options...
ridgerunner Posted December 11, 2003 Report Share Posted December 11, 2003 Hi Been a few months since I have been here. This problem comes up pretty often. I posted about it some time ago. The cheapest and easiest repair I know of for bulging tops, caused by string tension, is the JLD Bridge Doctor. The have a web site or at least they did, just search by their name. Also, Stew-Mac sells the product. I installed one on an Alvarez 6 string. They work and also improve the sound of your guitar and they are very reasonable in price. They are friendly and helpful if you wish to call them. You can probably do the job yourself and make that old 12 string hum once again. (By the way, I do not work for Bridge Doctor) Quote Link to comment Share on other sites More sharing options...
rockinrobert Posted December 12, 2003 Author Report Share Posted December 12, 2003 Hey ridgerunner, thank you very much for the tip! I will check their site out immediately. Hope it works, may be a great beginner project for me. Thanks, bOb Quote Link to comment Share on other sites More sharing options...
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