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| Fixing a double (or composite) top http://www.luthiersforum.com/forum/viewtopic.php?f=10101&t=23641 |
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| Author: | patmguitars [ Mon Aug 31, 2009 2:33 pm ] |
| Post subject: | Fixing a double (or composite) top |
Hi folks My first attempt at a composite top came out pretty well. It has three layers: top is Spruce, bottom is Cedar, and the middle part is Cedar and Balsa. After a couple of days, I noticed that a very small area, just a bit larger than a postage stamp, has come unglued. I used epoxy and this little area lifts up ever so sligthly and by pressing it down with my finger, I can feel that only the top layer of Spruce (aboaut 7 to 8 tenths of a mm thick) is unglued. The area is very near the end block, and this has no effect whatsoever on the sound. The only option that I have come up with so far, apart from taking the whole top off, is to make a very thinny hole at the center of the unglued area, inject some cyano glue (the most liquid one) and press with clamps. Any other suggestions? Cheers Pat |
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| Author: | Steve Saville [ Mon Aug 31, 2009 4:13 pm ] |
| Post subject: | Re: Fixing a double (or composite) top |
Pat, Your repair might work, but CA is not a good choice for gluing epoxy coated wood. Epoxy is a much better choice. I'm thinking that you need to pull the top. If one area is showing poor adhesion, chances are the whole top is problematic, unless you used a different method for the portion that is delaminating. Sorry, but I think you should make another top to help you better develop your process of bonding the 3 layers. I've made a double layer and had to rebuild it, also for poor adhesion. Do not skimp on the epoxy or you'll have trouble. The flip side is that you want to make it light. |
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| Author: | patmguitars [ Tue Sep 01, 2009 7:21 am ] |
| Post subject: | Re: Fixing a double (or composite) top |
Hi Steve I am fairly sure it will come to replacing the top, but I am going to try to repair it just to experiment. So far, only this little spot seems to have come unglued, so I am going to keep playing it for a couple of weeks, just to see if anything else pops up. I certainly agree with you about the amount of epoxy being the critical factor. I just bought some epoxy made especially for wood at LMI and I'll give it a try on another composite top. Thanks for the input. Pat |
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| Author: | JJ Donohue [ Tue Sep 01, 2009 7:38 am ] |
| Post subject: | Re: Fixing a double (or composite) top |
I would abandon this top and learn from it via the good old post-mortem autopsy. Make improvements on the next trial based upon that which you find. It wasn't clear how you clamped your laminate. From reading other posts over the years, it seems that those who have used a vacuum setup similar to that which the veneer folks have used for years seem to achieve consistently uniform and quality glue joints. Vacuum also provides for a thin glue line when using epoxy...something that reportedly helps significantly with the mass and dampening issues. Disclosure: I have not tried this yet, but I have taken lots of notes for some time now. Those who have had consistent and repeatable success all used vacuum jigs. |
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