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| Side Crack while Bending http://mowrystrings.luthiersforum.com/forum/viewtopic.php?f=10101&t=40623 |
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| Author: | Goodin [ Tue Jun 11, 2013 8:15 am ] |
| Post subject: | Side Crack while Bending |
I'm on my 7th build and I have made my first side crack while bending. I am bending mahogany (which is a pain in my experience, lots of spring back) free hand on a hot pipe. Nearing the last 3/4 of the bending process I got impatient and tried to move too fast, and, pop! A cross grain crack developed about an inch long. It's in a not-too-curvy section, just above the upper bout. Can I save this piece? I was thinking thin CA glue might work, but I am worried that when I get back to bending, the heat might undo the glue joint. Any way to make a cross grain crack invisible? Thanks for any suggestions. |
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| Author: | Goodin [ Tue Jun 11, 2013 1:42 pm ] |
| Post subject: | Re: Side Crack while Bending |
Thanks Todd. I'll give that a try. I will be staining it, Martin 18 style. Hopefully it won't show up. Any suggestions to hide it better under stain? |
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| Author: | Kevin Waldron [ Tue Jun 11, 2013 6:02 pm ] |
| Post subject: | Re: Side Crack while Bending |
You might try taking some 2 part epoxy and squeeze it into a Ziplock bag, add small amount aniline powder dye ( your color stain.... you may need to experiment to know how much to add to get your color...... the dye will slow the epoxy down in drying but we have used this in knots and cracks for 40+ years and all are still inplace ). Mix between the fingers snip end squeeze out on crack/split.....use shop vacuum on the back side of the material and suck the glue through to the other side. Use wax paper and a cowl to clamp and allow to dry. Blessings, Kevin |
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| Author: | Pmaj7 [ Tue Jun 11, 2013 6:35 pm ] |
| Post subject: | Re: Side Crack while Bending |
Kevin Waldron wrote: ...epoxy and squeeze it into a Ziplock bag...Mix between the fingers snip end squeeze out.....use shop vacuum on the back side of the material and suck the glue through to the other side. 2 great new ideas, thanks Kevin! |
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| Author: | Goodin [ Wed Jun 12, 2013 7:37 am ] |
| Post subject: | Re: Side Crack while Bending |
Thanks for the advice fellas. I used CA glue last night and it worked ok, but the crack was still noticeable, and as soon as I put it back on the hot pipe the crack opened back up. I'm thinking I will just start over. I realized I have a sister set i can rob the sides from for a good match. Kevin, your epoxy idea is brilliant. I'll keep that in mind if I'm working with more valuable wood. |
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| Author: | MikeyV [ Thu Jun 13, 2013 11:09 am ] |
| Post subject: | Re: Side Crack while Bending |
Just to add a bit of experience, on my third guitar, I created a bit of a cross grain crack in the upper bout curve, on a mahogany side. It was about 1/2" long, down from the top binding area. I finished bending, built the rims then stabilized with CA. After staining and varnishing, it's still visible, but not something anyone would notice. It was an early guitar, if it was for a client, I'd probably have replaced the side (both sides to match). |
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| Author: | Goodin [ Thu Jun 13, 2013 8:04 pm ] |
| Post subject: | Re: Side Crack while Bending |
This one is for a client (my first commission, a good friend), so I decided to start over with a fresh set of matching sides that match the back nicely. I am super frustrated with this mahogany! The spring back is unbelievable! I have spent the past three hours trying to bend one side and it's like wrestling a snake. I'll get the lower bout right on the template, start on the upper bout get it looking good, then the lower bout pops back out a few inches, then I work on it and the upper bout pops out a few inches...then the waist straightens out, then start the whole process all over. I finally gave up and clamped it in the mold before I broke it over my knee. I had to use quite a bit of clamp pressure to get it to fit the mold in some areas. I hope that's ok because I'm not messing with it anymore. I'm so absurdly frustrated I'm thinking about giving up building and selling all my stuff. Sorry, had to vent. So, is it acceptable for mahogany to not fit perfectly to the mold? I can get it to fit with moderate pressure. I'm hoping the side will relax to it's proper shape. I will never, ever again bend mahogany by hand. |
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| Author: | Clinchriver [ Thu Jun 13, 2013 8:25 pm ] |
| Post subject: | Re: Side Crack while Bending |
Gil I had some Honduras Mahogany that was a real pita........ to bend. Got some good advice and got a handle on the process. I use a bender/heating blanket, if you want to swing by I'll bet we can get it bent and in the mold satisfactorily . |
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| Author: | John Arnold [ Thu Jun 13, 2013 11:37 pm ] |
| Post subject: | Re: Side Crack while Bending |
Quote: So, is it acceptable for mahogany to not fit perfectly to the mold? Yes. It may not be the ideal, but I have made it work on many occasions....primarily when using Martin pre-bent sides (Indian RW, koa, and mahogany). In general, spring back occurs when there is moisture left in the wood. In my experience, bending until all the moisture is gone (and holding the shape until the side cools) is the remedy. I bend everything on a hot pipe. I have an Overholtzer side bender that I inherited when buying out another luther, but I have never plugged it in. When I have had a small repairable crack that occurred during bending, I finish the bending process before doing any gluing. This can usually be done by using a backstrap over the cracked area. |
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| Author: | Goodin [ Fri Jun 14, 2013 7:39 am ] |
| Post subject: | Re: Side Crack while Bending |
Thanks for the advice fellers. John, I have been bending wet, then when the particular section dries out completely I will take it off the pipe while trying to hold the shape with pressure and wetting that section again with a squirt bottle. Maybe I don't need to wet it the second time until it cools. |
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| Author: | LarryH [ Fri Jun 14, 2013 9:58 am ] |
| Post subject: | Re: Side Crack while Bending |
I have 4 guitars I'm building as a process exercise and tone development - all Mahogany. I built a Fox style bender and when bending my first hog sides I used similar temps for the Black Walnut I had been using, up to maybe 300 - 310 then cook for a little longer around 250. Really bad spring back with the mahogany. I then upped the temps to 350 + even touching 375 and let it cook for 20 minutes at around 275 - 300 and it held its shape pretty well, but still had some spring back and I'm resigned to think that hog just plain springs back. Oh BTW I used much more water than most recommend as well. BUT, if you build spreaders for your mold like Fillippo has shown above that cover most of the sides (I have almost identical shaped and sized spreaders) AND you use solid linings the sides will maintain their shape very, very well even out of the mold. Check this thread for some lining ideas. viewtopic.php?f=10101&t=40613 Linings should net out IMO around 5/16" and you can use multiple laminations to get there. The down side is you might have to bend your linings as well and dealing with those narrow pieces can cause breakage which may also cause you to want to give up building guitars as well. So for me the bottom line with Mahogany is bend hot, hot, hot. Get your sides into your mold anyway you can that keeps the mold's shape then use solid linings to keep that shape. |
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