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| Repairing an unbraced cracked soundboard? http://www.luthiersforum.com/forum/viewtopic.php?f=10101&t=47219 |
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| Author: | James Orr [ Sat Feb 06, 2016 2:45 pm ] |
| Post subject: | Repairing an unbraced cracked soundboard? |
That feeling you get when you plop down your arm down to do a little layout and crack an LS redwood top? Yeah. Not great. But tolerable, knowing it should be easy to repair. Only, I've never done it. Thankfully this is a very clean crack, so I expect it to be easy. My thought was to use my LMI glue, but I wanted to bring it up here, first. The bulk of the crack is easy to get to, but I'm not sure how to make sure the glue wicks to the very end of the crack to prevent it from spreading in the future. Any tips would be fantastic. Thanks in advance. Attachment: IMG_5374.jpg
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| Author: | Hesh [ Sat Feb 06, 2016 3:02 pm ] |
| Post subject: | Re: Repairing an unbraced cracked soundboard? |
Hey James. Redwood does this with no warning so don't feel bad. If you have plenty of thickness getting everything perfectly level is not as critical although I suspect that it will go back together level anyway. Collagen glues can attract parts together and might be a good way to go here. Or just good, ole Titebond original would be fine too. Lately I've been sizing cracks, no jokes please, well maybe a few... by using half strength TB to pre-wet the inside of the crack and help attract the full strength stuff that I follow up with. Wash hands first because any dirt on your hands will permanently discolor the crack. Either rub in glue with your finger and/or use compressed air to blow the glue into the crack. You could clamp this one with a Spanish Tourniquet style jig that would help push the pieces together and keep things level. Lots of approaches to fixing this. |
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| Author: | James Orr [ Sat Feb 06, 2016 3:17 pm ] |
| Post subject: | Re: Repairing an unbraced cracked soundboard? |
I thought you'd come to the rescue. Thanks, Hesh. So you you would first dampen the wood with thinned glue, then come at it with full strength glue, using an air compressor to blow it into the depths? |
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| Author: | DennisK [ Sat Feb 06, 2016 3:22 pm ] |
| Post subject: | Re: Repairing an unbraced cracked soundboard? |
Happens all the time. Hot hide glue, with a bit more water than usual. Warm the wood, slop a generous amount of glue on both sides, and flex the crack open back and forth to vacuum the pool of glue into it. Squish at it with your fingers some too, for good measure. Get it lined back up perfectly and you'll have a tough time finding it again later 
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| Author: | david farmer [ Sat Feb 06, 2016 3:38 pm ] |
| Post subject: | Re: Repairing an unbraced cracked soundboard? |
+1 If you keep it under a heat lamp while your working in the thinned hide, you'll have lots of time to keep adding hot glue and working it in there. |
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| Author: | wbergman [ Sat Feb 06, 2016 3:54 pm ] |
| Post subject: | Re: Repairing an unbraced cracked soundboard? |
DO NOT USE CA. I used CA once and it discolors redwood, even if wicked in from the opposite side. |
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| Author: | Rod True [ Sat Feb 06, 2016 4:04 pm ] |
| Post subject: | Re: Repairing an unbraced cracked soundboard? |
Sound advise. Also when it's fixed if your worried (which you shouldn't be) you can flip the pattern and get the cracked area outside of the layout. |
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| Author: | Hesh [ Sat Feb 06, 2016 4:13 pm ] |
| Post subject: | Re: Repairing an unbraced cracked soundboard? |
James Orr wrote: I thought you'd come to the rescue. Thanks, Hesh. So you you would first dampen the wood with thinned glue, then come at it with full strength glue, using an air compressor to blow it into the depths? Something like that. More specifically I'm looking for other ways to draw the glue into the crack because flexing and Redwood can ruin your day...   IME Redwood tends to snap with little or no warning and since part of the top is still not cracked why risk letting the crack travel.HHG with heat is a great way too. Again lots of ways AND glues to do this with and your best bet will likely have a lot to do with what you have and what you are comfortable with. By the way the more time I spend in this trade the more I am becoming convinced that many of the methods, materials, and approaches that we often ponder the possibilities even to the point of assigning mystical, vintage, blah, blah, blah about the answer was likely far more simple. They did what they did and used what they used because it was what they had... Sorry to digress there.
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| Author: | Rod True [ Sat Feb 06, 2016 4:19 pm ] |
| Post subject: | Re: Repairing an unbraced cracked soundboard? |
As far as drawing glue into the crack you can use your shop vac to do that too.... |
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| Author: | James Orr [ Sat Feb 06, 2016 7:32 pm ] |
| Post subject: | Re: Repairing an unbraced cracked soundboard? |
Rod True wrote: Sound advise. Also when it's fixed if your worried (which you shouldn't be) you can flip the pattern and get the cracked area outside of the layout. I totally would, but it's an irregularly shaped set. Only one end is wide enough for the lower bout. Thanks for the ideas, everyone! |
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| Author: | Bri [ Sat Feb 06, 2016 8:11 pm ] |
| Post subject: | Re: Repairing an unbraced cracked soundboard? |
Titebond and a set of feeler blades, lay a bead of glue along the crack and slip the blade up and down to drag the glue through. Wipe off the excess and pull snug with masking tape. Something like .015 blade. |
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| Author: | Imbler [ Sat Feb 06, 2016 9:46 pm ] |
| Post subject: | Re: Repairing an unbraced cracked soundboard? |
No one has mentioned it, and I may be overly conservative, but I would cleat it as well. You can't get glue into the crack all the way to where it ends in solid wood, so it leaves a wicked stress concentration point where the crack ends. I would at least cleat it at the end of the crack. But... I'm a worrier, Mike |
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| Author: | Hesh [ Sun Feb 07, 2016 7:30 am ] |
| Post subject: | Re: Repairing an unbraced cracked soundboard? |
Imbler wrote: No one has mentioned it, and I may be overly conservative, but I would cleat it as well. You can't get glue into the crack all the way to where it ends in solid wood, so it leaves a wicked stress concentration point where the crack ends. I would at least cleat it at the end of the crack. But... I'm a worrier, Mike I'm a worrier too so I can relate Mike. In this case though the top is yet to be braced and the bracing will also act as cleats of sorts AND if we build stress free too (not worrying about the game tonight or income taxes, etc. it should be OK.
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| Author: | James Orr [ Mon Feb 08, 2016 1:14 pm ] |
| Post subject: | Re: Repairing an unbraced cracked soundboard? |
As you can see in the pic, the crack is just a little over an inch in from the widest part of the lower bout, and it ran nearly all the way through, stopping about an inch short (of going all the way through the lower bout). Yesterday during the game I kept thinking about how much more confident I'd feel about getting glue everywhere important if the crack just ran all the way through the lower bout, because then, frankly, I wouldn't have to do anything crazy to get the glue drawn all the way to the very end. So, this morning I cracked it further. A medically induced fracture, if you will  I slid a thin metal rule through the crack like a froe, slowing forcing the crack to open further and further along the top. The results were clean, and getting a glue through all the important surfaces should be simple now. I just didn't want to run the risk of getting it almost entirely glued and should have a strong glue joint throughout now.
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| Author: | Rod True [ Mon Feb 08, 2016 4:43 pm ] |
| Post subject: | Re: Repairing an unbraced cracked soundboard? |
Good idea! We'll all pray to the router bit gods that there is no blow out when cutting the binding channels for that redwood..... |
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| Author: | Hesh [ Mon Feb 08, 2016 4:48 pm ] |
| Post subject: | Re: Repairing an unbraced cracked soundboard? |
Climb cuts are your friend.... Mine too!
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| Author: | Woodie G [ Mon Feb 08, 2016 5:29 pm ] |
| Post subject: | Re: Repairing an unbraced cracked soundboard? |
I just got to do one of these! I found an old redwood top that had been set aside for some reason, and I certainly found out why...there I was tapping and flexing as if I knew what I was doing, and with a pop, a crack about 8" long in the center of the bass half let go. The boss said fix it, and demonstrated the methodology on a bit of scrap. The crack ran to just short of the waist and needed another inch to end in waste wood outside the body shape. After reinforcing the upper bout by clamping between two cork-lined cauls, I opened the crack to outside of the top outline, then glued. I was reassured that - as the crack was fresh and would run edge to edge on the outline, it was as unlikely to fail as any other well made glued seam and needed no encouragement with cleats to hold fast provided the glue line was well and truly closed. For adhesive, I was directed to use hot hide glue (I think the high clarity brand), and specifically, about an ounce from the freshly made stuff in the glue pot, thinned to very runny, then heated to 180 degrees Fahrenheit in the hot pot for better penetration and open time. HWMBO(WAS) noted that the unused glue should be discarded after the overheat (on reheat, it will have lost far too much strength due to the cooking), but between warming the top with a standard heating pad to 110-115 degrees Fahrenheit and the higher heat of the glue, excellent penetration was achieved to the point of failure, as we later verified. I clamped with filament-reinforced tape and then used the wedge and caul top clamping jig for a bit of insurance. I was also reminded that a heat gun set to low would do a rather nice job of reflowing the glue if necessary, and that contrary to my general experience, gravity is your friend when flowing or reflowing glue Once the crack dried, we joined the top and trimmed to size, which allowed us to do a bit of destructive testing on the off-cut...the glue penetrated to the entire length of the crack, and there was no evidence of further issue. Good luck, Mr. Orr - I love redwood tops, and particularly the older salvaged material we use here when we can obtain it from Mr. Maize. |
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| Author: | Rod True [ Mon Feb 08, 2016 8:14 pm ] |
| Post subject: | Re: Repairing an unbraced cracked soundboard? |
Hesh wrote: Climb cuts are your friend.... ya but it's redwood...... Mine too!
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| Author: | Ken Franklin [ Mon Feb 08, 2016 11:37 pm ] |
| Post subject: | Re: Repairing an unbraced cracked soundboard? |
The problem with redwood, even LS, is that though the crack has appeared to stop there is weakness just past that point and since it hasn't been braced you are better off cracking it the entire length of the board. Then use hot hide glue to make the repair. I like the tape method. I use the green 3M stuff. Pull tape across the seam on one side only. That will flex the seam open. Apply hot hide glue. Lay it flat on the reverse side. Pull tape across the seam on that side. You won't have to worry about something showing up later down the building road. |
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| Author: | James Orr [ Mon Feb 08, 2016 11:46 pm ] |
| Post subject: | Re: Repairing an unbraced cracked soundboard? |
Rod True wrote: Good idea! We'll all pray to the router bit gods that there is no blow out when cutting the binding channels for that redwood..... Hesh wrote: Climb cuts are your friend.... Mine too!And a little luck from my handy Canadian Luthier Supply Gramil.
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| Author: | Hesh [ Tue Feb 09, 2016 7:04 am ] |
| Post subject: | Re: Repairing an unbraced cracked soundboard? |
James Orr wrote: Rod True wrote: Good idea! We'll all pray to the router bit gods that there is no blow out when cutting the binding channels for that redwood..... Hesh wrote: Climb cuts are your friend.... Mine too!And a little luck from my handy Canadian Luthier Supply Gramil. Yep the Gramil is a vey good idea too! |
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| Author: | John Lewis [ Tue Feb 09, 2016 7:29 pm ] |
| Post subject: | Re: Repairing an unbraced cracked soundboard? |
Thinned hot hide glue and a suction cup works well - then clamp. |
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| Author: | James Orr [ Tue Feb 09, 2016 7:57 pm ] |
| Post subject: | Re: Repairing an unbraced cracked soundboard? |
That's very interesting. What do you mean by a suction cup? |
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| Author: | Joe Beaver [ Tue Feb 09, 2016 9:48 pm ] |
| Post subject: | Re: Repairing an unbraced cracked soundboard? |
I like Brian's feeler gauge idea. But a suction cup sounds good to. Maybe both!!! |
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| Author: | John Lewis [ Wed Feb 10, 2016 7:00 pm ] |
| Post subject: | Re: Repairing an unbraced cracked soundboard? |
Suction cup glue vids- https://www.youtube.com/watch?v=6DwA56TKWq8 https://www.youtube.com/watch?v=yvP565-YJ_g I love watching Dan fix stuff! |
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