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| Follow up on crack repair of 1969 Guild F20 http://w-ww.luthiersforum.com/forum/viewtopic.php?f=10101&t=16838 |
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| Author: | Todd Rose [ Sun Apr 13, 2008 12:54 am ] |
| Post subject: | Follow up on crack repair of 1969 Guild F20 |
My question about the two long cracks on the top of this guitar (see photo below) is, basically, how do you decide when to leave cracks alone and when to repair them? In this case, there are no loose braces, the cracks are closed when the guitar is properly humidified, there are no odd noises, the guitar is holding up well structurally, and it sounds great. |
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| Author: | Cal Maier [ Sun Apr 13, 2008 8:56 am ] |
| Post subject: | Re: Follow up on crack repair of 1969 Guild F20 |
Hi Todd, This may be just my opinion on this subject but I feel that the cracks, no matter how tight they get when humidified should still be fixed. I think with proper repair, the sound of this instrument will improve even more. Reason: The plate will work as one unit as opposed to two or three pieces held together by the bracing. If not, why do we bother joining our top plates, why not just butt them up and brace them in place? Like I said, my opinion. Cal |
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| Author: | David Collins [ Sun Apr 13, 2008 11:00 am ] |
| Post subject: | Re: Follow up on crack repair of 1969 Guild F20 |
I would certainly glue the cracks behind the bridge along with the pickguard cracks. I have to say though, that it's a bit odd to see what appears to be an extension of the same crack continuing behind the bridge that began in front. If the bridge and plate were fully secure it would be odd that they allowed the crack to travel through. Makes me wonder if the bridge was previously loose when the crack occurred, and may have since been reglued (assuming it's secure right now). Or of course it could just be coincidence that a dryness crack appeared behind the bridge in the same line as the pickguard crack in front. Different causes, same line? In any case, I would reglue it. If the crack is tight together, the heat gun trick can be an extra boost to bring glue down in to the crack. It's fairly common practice to wet the crack with hot water from the glue pot, then work hide glue in to it, thinning slightly as it's being rubbed in with the warm water, and pushing up on the inside to spread it slightly. On the very tight cracks I will occasionally pull out the heat gun though, and warm from the inside just like the pickguard trick. Start with a bit of warm water on the crack, and heat from the inside a few minutes until you see it start to draw down and dry on the outside. Then start rubbing in a bit of hot hide glue, thinning a bit as you go. By heating and drying the bottom you will effectively be keeping the bottom dryer and more actively wicking and pulling the moisture with it. Of course the moisture at this point is carrying hide glue with it, and should draw it in to the tight bottom of the crack more aggressively. It also brings the bonus of keeping the area warm to extend the gel time of the hide glue, hopefully allowing a little better penetration before it dries and gels. I admit, I've had no way to really test to see if this is more effective than just rubbing in the water and glue. Still, it makes enough sense in theory (and does extend the gel time) that I like to do this on tight cracks that can't really be pried open. |
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| Author: | Stefan [ Sun Apr 13, 2008 1:19 pm ] |
| Post subject: | Re: Follow up on crack repair of 1969 Guild F20 |
Hi guys, I'm real interested in this crack repair thing. I've read in Don Teeter's book that to repair a crack in a top you take a knife to it, cutting a nice uniform slot with beveled edges into the top. Then you cut from a piece of spurce a splint with tapered edges trying to get the harder wintergrowth (the grain line) to line each side. Then this is to be glued in. I've seen someone do the job with a razor saw, one of those things you can get at a hobby shop, and stew mac sells this tool to cut the top: http://www.stewmac.com/shop/Tools/Foredom_tools,_attachments/1/PowerKnife.html I've fixed one cracked top, but it was a little different than what you are working on. This was a guitar that was stepped on. There were 3 pieces that were semijoined and stuffed into the box. I pulled them out and used titebond to stick em back together, no knife work to even up gaps and fill with extra spruce. Looked alright, but I refinished the whole top. Besides a complete refinish of the top, I really didn't know how to "touch up" the repair to make it look right. Question, when to inject glue in (HHG, I know now is to be preferred) and when do you do the knife surgery? Peace, and thanks for all the insight. Stefan |
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| Author: | David Collins [ Sun Apr 13, 2008 5:05 pm ] |
| Post subject: | Re: Follow up on crack repair of 1969 Guild F20 |
I would say I do spline work on well under 1% of the top cracks I repair. It's very invasive and much more labor intensive, and I need good reason to cut in a spline. There has to be a good reason, such as significant wood missing, or a top that was built far too green and would doomed to split again even in good humidity. So my answer as to when to do knife surgery - almost never. |
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| Author: | Evan Gluck [ Sun Apr 13, 2008 5:56 pm ] |
| Post subject: | Re: Follow up on crack repair of 1969 Guild F20 |
I agree with David here, I did dozens of crack repairs last year and when I looked at my records just 1 splint. Less is best. Best, Evan |
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| Author: | Cal Maier [ Sun Apr 13, 2008 9:21 pm ] |
| Post subject: | Re: Follow up on crack repair of 1969 Guild F20 |
I'm with you fellers(David & Evan), when it comes to crack repair I try to stay away from the knife if at all possible. Humidify and wick in the glue then cleat. Cal |
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| Author: | Todd Rose [ Sun Apr 13, 2008 10:05 pm ] |
| Post subject: | Re: Follow up on crack repair of 1969 Guild F20 |
Thanks a lot, guys! All of your help is hugely appreciated. David, you're probably right about the one crack occurring at a time when the bridge was loose. The bridge has, in fact, been reglued by somebody in the past. It was done somewhat sloppily, but it's holding, so I don't plan to take it off and reglue it. |
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