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| Tight spruce top crack in unfinished top, not humidity crack http://www.luthiersforum.com/forum/viewtopic.php?f=10101&t=30308 |
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| Author: | My Dog Bob [ Mon Dec 13, 2010 9:52 am ] |
| Post subject: | Tight spruce top crack in unfinished top, not humidity crack |
Box is closed up. 2-1/2" Crack happened by over clamping near the tail block. You can't see the crack but you can feel it. Unfortunately, the guitar has a small sound-hole and I can't get inside to flex the crack open... It's so tight that I am not sure it would open up anyway. I am extremely careful with humidity control on glue-ups so it certainly wasn't that. Guitar is ladder-braced so the crack cannot go any further. Not certain what to do here.. From what I understand, Cyano will (possibly) discolor the spruce (German Spruce by the way). Don't see being able to get Hide or LMI in there... It's a stinker.. Any thoughts? Thanks, Peter Z |
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| Author: | Pat Foster [ Mon Dec 13, 2010 11:42 am ] |
| Post subject: | Re: Tight spruce top crack in unfinished top, not humidity crack |
Peter, Make a "jack," which looks sort of like a small hockey stick. Shape it so that you can snake it in through the soundhole and use it as a lever to push up on the crack from inside. The heel of the stick would bear against the back with the toe bearing up against the crack. You'll likely want to put a caul on the back to keep from cracking it too. The upward pressure on the top will cause the crack to open so that you can work some HHG or white/yellos glue into it. I'd avoid CA. Good luck! Pat |
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| Author: | tlguitars [ Mon Dec 13, 2010 11:46 am ] |
| Post subject: | Re: Tight spruce top crack in unfinished top, not humidity crack |
And water down your glue. If it's as tight as you say it is then add a few drops of water to say a nickels worth of glue. Mix it with a q-tip on some plexi glass and then you can bleed it in for a more complete penetration. |
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| Author: | wolfsearcher [ Mon Dec 13, 2010 1:43 pm ] |
| Post subject: | Re: Tight spruce top crack in unfinished top, not humidity crack |
just curious does anyone use a syringe for this for pushing the glue in if so do you have any tips ? your recommended nossle diameter /some sort of seam plunger anyone try something like this |
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| Author: | Imbler [ Mon Dec 13, 2010 2:07 pm ] |
| Post subject: | Re: Tight spruce top crack in unfinished top, not humidity crack |
Someone in this forum mentioned he blows glue into cracks using low pressure compressed air. I haven't had occasion to try it, but it certainly sounds like it would work well even on a fairly tight crack. It reminds me of the way they gave shots in the army, by just blowing the vaccine through your skin with no needle, Mike |
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| Author: | My Dog Bob [ Mon Dec 13, 2010 2:49 pm ] |
| Post subject: | Re: Tight spruce top crack in unfinished top, not humidity crack |
Anything is possible but I doubt that low presure compressed air would push anything through the crack I am talking about. It's just as tight as can be.. maybe if I really dehumidified it first. As far a putting a jack inside. I guess I'll work on some sort of apparatus (Soundhole is tiny). Unfortunately the back is very delicate and I am sure if I flexed the top enough to open up the crack by pushing against the back, I'd certainly crack the back - unless I can bridge the back braces for support. This could be tricky It's a stinker. Thanks for all of your input though. It will all factor in to what I do.. Peter Z |
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| Author: | Ken Franklin [ Mon Dec 13, 2010 4:49 pm ] |
| Post subject: | Re: Tight spruce top crack in unfinished top, not humidity crack |
If you build with a radius dish, you can clamp the body in the dish before you jack open the crack. |
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| Author: | My Dog Bob [ Mon Dec 13, 2010 5:08 pm ] |
| Post subject: | Re: Tight spruce top crack in unfinished top, not humidity crack |
It's radiused but not with a dish. I wouldn't have support under that area with my arching forms.. PZ |
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| Author: | Andy Birko [ Mon Dec 13, 2010 6:50 pm ] |
| Post subject: | Re: Tight spruce top crack in unfinished top, not humidity crack |
Test the CA on a piece of scrap top from this build or on a similar piece of top (I keep the scraps on my shop floor for safe keeping). Apparently there's two ways to make CA glue and only one of them stains. If I recall, Jet brand CA does not stain but definitely test first. My local hobby store brand does. The other thing is that if the CA does stain, it's much worse on end grain than long grain so it might not show up even if it is the staining type. |
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| Author: | DennisK [ Mon Dec 13, 2010 8:40 pm ] |
| Post subject: | Re: Tight spruce top crack in unfinished top, not humidity crack |
Watered down hide glue would probably wick in there. Make sure you warm the area up a bit first. I brush it on with a paintbrush. Really extreme, you could router about half way through the top and inlay a piece of matching spruce to make sure the crack never spreads. If you dry it out to open up the crack, it may spread... I'd do the watery hide glue. |
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| Author: | truckjohn [ Mon Dec 13, 2010 10:49 pm ] |
| Post subject: | Re: Tight spruce top crack in unfinished top, not humidity crack |
Watch out on compressed air.... You can literally blow the top of a guitar into pieces with only a few PSI.... All you gotta do is lay your hand over the soundhole for a bit and Ka-Pow... Vacuum cleaners are also similarly dangerous.... Thanks |
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