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| Bummer, Top Cracked Down Center Seam http://www.luthiersforum.com/forum/viewtopic.php?f=10101&t=31189 |
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| Author: | Darryl Young [ Sat Feb 19, 2011 7:50 pm ] |
| Post subject: | Bummer, Top Cracked Down Center Seam |
Finished my buffer and buffed my guitar this afternoon. It's warm here today, in the 70s and much more humid than it has been. Even warm inside with no heat or air running. Just noticed the finish is cracked down the center seam where the bridge will be glued. The crack is about 2" long. I really can't say for sure if the top is cracked or just the finish, but since it's perfectly down the center seam I assume the top has pulled apart slightly. The finish on the top is very thin. Any suggestions how to handle this? Probably the good news is I will soon glue a giant cleat (the bridge) over the crack. The crack will extend below the rear of the bridge. Maybe I will know more when I've removed the finish for glueing the bridge. I wonder if the crack will still show if the humidity drops? Here is a pic but I couldn't get a good shot where the crack shows well. I put red pointers roughly where the crack starts and stops. Attachment: SmallPointersToCrack.jpg
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| Author: | Mike Baker [ Sat Feb 19, 2011 8:04 pm ] |
| Post subject: | Re: Bummer, Top Cracked Down Center Seam |
Bummer is right. that would absolutely suck! But there are people here who have dealt with that and a lot more. I hope they chime in soon and give you an answer. Again, that really bites! Sorry. |
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| Author: | Mark Groza [ Sat Feb 19, 2011 8:11 pm ] |
| Post subject: | Re: Bummer, Top Cracked Down Center Seam |
That's a bummer for sure Darryl. What finish did you use and which glue? More humidity will probably close it up. |
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| Author: | Darryl Young [ Sat Feb 19, 2011 8:39 pm ] |
| Post subject: | Re: Bummer, Top Cracked Down Center Seam |
The finish is KTM-SV. Super glue sticks to it but I don't want to stain the top. The soundboard seam was glued when I received it but it's very likely Titebond. John Hall recommended I probe and see if the wood is cracked. I couldn't get a 0.0015" feeler gauge in the crack in the finish. John mentioned that wood usually seperates going to low humidity rather than going to high humidity. So maybe this is just a finish crack. If I finish the bridge tomorrow, I'll try to locate it and remove the finish and I can see what is going on for sure. I'll post an update. I'm not that concerned about a finish crack. |
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| Author: | Elman Concepcion [ Sat Feb 19, 2011 9:34 pm ] |
| Post subject: | Re: Bummer, Top Cracked Down Center Seam |
No Biggie. Check your RH. Make sure it is low = under 40% or better under 35%. Stick a mirror inside. Flex the top, up and down from the inside, to see the extend of the separation. It might only show from the outside and that would be good. If that is not the case, it does not matter, the procedure is the same.. Make some HHG. Warm up the seam carefully = just slightly warm to the touch. Percussively with your finger smack some HHG into the separation while flexing the joint. Work quickly - you don't have a lot of time. 10 minutes at 80 degrees Fahrenheit and it goes down from there the cooler your shop. Plan on less than 3 mins at 72 degrees Fahrenheit. If you can get your workshop up to 80 degrees Fahrenheit - that would make the procedure less stressful. Look inside to see that HHG migrated through. Leave extra HHG over the finish. Leave extra HHG on the inside. Raise RH to Higher than 60% Make sure the surfaces are level. Levelers with wax paper or Plexiglas with wax on it are good for this. Small magnets are a joy to use for this application The next day. Wipe gently with slightly damp cloth until there is no more HHG on the surfaces. You are done. Hope that helped. Elman Maybe a some tiny cleats might be in order. Very thin. Small magnets are a joy to use for this application as well. |
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| Author: | johnparchem [ Sat Feb 19, 2011 11:10 pm ] |
| Post subject: | Re: Bummer, Top Cracked Down Center Seam |
Darryl isn,t the bridge plate right under where the crack happened? It should act as giant cleat. I have trouble understanding how the wood could seperate there. If you had to force the bridge plate in place maybe you opened a small crack when you glued it in. |
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| Author: | Mark Groza [ Sun Feb 20, 2011 8:11 am ] |
| Post subject: | Re: Bummer, Top Cracked Down Center Seam |
I would be sure to look inside to see if the bridge plate is cracked. It's possible that if it is, that's what cracked the top. If it's a rosewood plate that wasn't seasoned properly, that will do it.Rosewood is good for cracking as it dries out from low humidity.At night in a dark room, shine a light inside of the body to see if light is coming through the plate. |
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| Author: | es guitars [ Sun Feb 20, 2011 9:26 am ] |
| Post subject: | Re: Bummer, Top Cracked Down Center Seam |
I've always questioned the process of gluing the bridge plate at a different grain direction than the top. Because the wood movement is different between the two grain directions. It is a small area so I assume it really should'nt be a problem. Maybe the top was'nt completely dry. I learned this the hard way building furniture glueing large areas of solid wood against the grain. It accutaly woke me up at night with a massive cracking sound. the wood wants to move, if its held tight(glued) it will crack. Hope this helps. Brent |
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| Author: | TonyKarol [ Sun Feb 20, 2011 11:11 am ] |
| Post subject: | Re: Bummer, Top Cracked Down Center Seam |
I would highly suspect that the outer face of the top moved due ot low humidity .. the bridge plate likely isnt cracked, and this is whats holding it together, along with the bridge itself. The top may move enough to fracture the finish, but the crack doesnt go all the way thru the wood. I have seen this happen with dry guitars ... |
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| Author: | bluescreek [ Sun Feb 20, 2011 4:13 pm ] |
| Post subject: | Re: Bummer, Top Cracked Down Center Seam |
I agree . I doubt it is the plate . I suspect that the crack is a finish crack. This was posted on another forum and there was a high RH . I have seen this happen that the wood swells enough to stress the lacquer on the joint . To fix this is not as bad as one may think . You can lift the finish by cutting carefull through it and lifting it . Then make the repair and fold the finish back using thinner directly onto the top and agitating with your finger. Allow to cure level sand hit a few coats and you should be good to go. |
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