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| Cocobolo Back Thickness http://www.luthiersforum.com/forum/viewtopic.php?f=10101&t=32812 |
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| Author: | Parser [ Sun Jul 10, 2011 9:18 am ] |
| Post subject: | Cocobolo Back Thickness |
Hey guys, I have a cocobolo back that I was in the process of thicknessing when I discovered that the glue joint was not up to par (I attempted to use titebond original on a freshly cut joint with abysmal results!). I'll never use titebond for cocobolo again - nothing but epoxy for me! The back is now at about .115 and I need to rejoint the edge. This is the thickness where I would like to end up - not start at. It's a beautiful set of wood and I hope I haven't made this thing into a ukulele set! What thickness do you guys use for cocobolo backs? Thanks in advance for any feedback. Best, Trev |
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| Author: | jackwilliams [ Sun Jul 10, 2011 10:20 am ] |
| Post subject: | Re: Cocobolo Back Thickness |
Trev, Just one old man's opinion and only based on a couple of coco builds, but I would consider a thinner back for coco... something more in the .090 range. Of course,take my suggestion with a grain of salt regards, jack |
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| Author: | Laurent Brondel [ Sun Jul 10, 2011 10:42 am ] |
| Post subject: | Re: Cocobolo Back Thickness |
Any glue works with cocobolo providing the surfaces are freshly planed, scraped or sanded. Attempting to clean the surfaces with acetone may have the opposite effect than the one desired (I think it may bring the oils to the surface). Thickness of the back depends on the set, guitar size and overall build philosophy. For me I can go as thin as .060" on a small single 0, on a bigger guitar maybe up to .070". Cocobolo is heavy and usually has higher internal damping than other rosewoods. |
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| Author: | Parser [ Sun Jul 10, 2011 10:44 am ] |
| Post subject: | Re: Cocobolo Back Thickness |
I wanted to ask the question because I typically build with thicker backs than most - I appreciate your thoughts & the sanity check they provide! Laurent, that's an interesting thought regarding acetone. I'm not messing around with titebond on the edge joint though - I'll stick with epoxy just to be sure. I'll probably use titebond everyone else. Thanks, Trev |
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| Author: | Laurent Brondel [ Sun Jul 10, 2011 10:59 am ] |
| Post subject: | Re: Cocobolo Back Thickness |
I sometimes use thin CA to glue the back halves. IMHO much less messy than epoxy… |
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| Author: | alan stassforth [ Sun Jul 10, 2011 11:46 am ] |
| Post subject: | Re: Cocobolo Back Thickness |
Laurent Brondel wrote: I sometimes use thin CA to glue the back halves. Really? I didn't think ca is very strong. |
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| Author: | Howard Klepper [ Sun Jul 10, 2011 1:13 pm ] |
| Post subject: | Re: Cocobolo Back Thickness |
................. |
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| Author: | Mike Collins [ Sun Jul 10, 2011 1:17 pm ] |
| Post subject: | Re: Cocobolo Back Thickness |
Trev what size guitar are you making? Nylon strung or steel? Mc |
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| Author: | jfmckenna [ Sun Jul 10, 2011 2:12 pm ] |
| Post subject: | Re: Cocobolo Back Thickness |
Even if that is your desired thickness what problems would occur by rejoining the two halves? As far as CA goes, from my tests it's incredibly strong stuff. |
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| Author: | Parser [ Sun Jul 10, 2011 4:43 pm ] |
| Post subject: | Re: Cocobolo Back Thickness |
This is a steel string, 25.4" scale length - the lower bout width is about 15.125 so it is a bit smaller than an OM. @JFMckenna - Anytime I join backs & tops I like to have some extra to allow for 'cleanup' of any misalignment between the two halves. You know the deal, I'm sure - that it is tough to get *perfect* alignment between the two parts when gluing up. I'm assuming I'll lose .005 to .010 just from this. The CA idea is really interesting - maybe I'll do some glue up strength tests with some of the scraps. If I do, I'll post them.. Best, Trev |
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| Author: | Don Williams [ Sun Jul 10, 2011 5:40 pm ] |
| Post subject: | Re: Cocobolo Back Thickness |
I like to go really thin with coco. Maybe .075-.085 at most. It's really heavy stuff. |
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| Author: | longdrive55 [ Sun Jul 10, 2011 9:50 pm ] |
| Post subject: | Re: Cocobolo Back Thickness |
With regards to using CA, I used CA to glue a broken Cocobolo back. It worked really well.......though I haven't built with it yet. It seems very solid though and taps the same as the unbroken side. I got the idea from one of John Hall's YouTube videos where he joins an EIR back with CA. I asked LMI about fixing the Coco back and they said either CA or Epoxy would work just fine. They also thought the acetone wipe would be a good idea. I did the wipe too. |
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| Author: | WaddyThomson [ Sun Jul 10, 2011 10:00 pm ] |
| Post subject: | Re: Cocobolo Back Thickness |
I had a Cocobolo back that I had joined with HHG, crack and break apart along a grain line. Center joint held fine. I glued it together with Epoxy, and it held perfectly. Can't even see the place where it cracked. |
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| Author: | Lavrov Guitars [ Sun Jul 10, 2011 11:47 pm ] |
| Post subject: | Re: Cocobolo Back Thickness |
I had done two coco's and my first set i glued up with titebond, and the seam broke apart nastily. it looked pretty bad, so i had to get some more (i wasnt TOO happy with the first set anyways). Second set i used epoxy, and it came out beautiful. And coco is really dense, i went with .90 and that was also about the thickness Mike Doolin suggested with cocobolo. But like always, thats just an estimate, it always depends on the set ![[:Y:]](./images/smilies/smiley20.gif "Thumbs Up") Good luck!
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| Author: | Jim Watts [ Mon Jul 11, 2011 12:00 am ] |
| Post subject: | Re: Cocobolo Back Thickness |
I make my coco backs about .090 -.095 I usually inlay my back strip which increases the bond line by quite a lot. |
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| Author: | Parser [ Mon Jul 11, 2011 11:11 am ] |
| Post subject: | Re: Cocobolo Back Thickness |
I've been thinking the same thing about a back strip Jim...I think this one may be getting one. There's no sapwood to worry about obliterating on this, so I can do it and still sleep at night..  Trev |
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| Author: | jfmckenna [ Mon Jul 11, 2011 3:08 pm ] |
| Post subject: | Re: Cocobolo Back Thickness |
Parser wrote: This is a steel string, 25.4" scale length - the lower bout width is about 15.125 so it is a bit smaller than an OM. @JFMckenna - Anytime I join backs & tops I like to have some extra to allow for 'cleanup' of any misalignment between the two halves. You know the deal, I'm sure - that it is tough to get *perfect* alignment between the two parts when gluing up. I'm assuming I'll lose .005 to .010 just from this. The CA idea is really interesting - maybe I'll do some glue up strength tests with some of the scraps. If I do, I'll post them.. Best, Trev Ah yes but I wouldn't worry about clean up too much, if you use Titebond you can clean up the show face pretty good with a damp rag then mostly you are just scrapping glue off the inside face. |
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