That is some good knowledge to have!!! Just sorry you had to come by it the hard way.
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| Bizzare Polyurethane Glue Event http://www-.luthiersforum.com/forum/viewtopic.php?f=10102&t=10367 |
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| Author: | LarryH [ Sat Jan 13, 2007 12:06 pm ] |
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I was trying to decide what kind of glue I'd use for gluing a lamination on my fret board and head plate - see Here I decided to use the polyurethane and layed up layers of W/(maple/B/W veneer onto the headplate. Put a couple of plywood cauls on each side and clamped it up. I saw the polyurethane doing is gooey-squeeze-out-expansion thing and thought dang I'll have some clean-up and some effort to get that thing apart along the edges. No big deal. Then it was time to glue the same combo on the fret board but this time I used some plastic wrap just to save the clean-up. When it came time to take the clamps off I was having trouble getting the plywood cauls off the glued up side. THE PLYWOOD WAS GLUED TO THE MAPLE VENEER!! I thought I was a huge bone head and just thought I put an extra layer of glue on the maple veneer and hung my head in beginner's luthier shame. Then I went to the plastic protected finger board and noticed the plastic would not come off. THE PLASTIC WAS GLUED TO THE VENEER AS WELL!!! The polyurethane had actually soaked, weeped, expanded through the veneer. So much had expanded through that it actually created a relief of a small knot in the 2 x 4 I used as a caul on the fret board. Needless to say both the fret board and head plate will probably not be savable. I'm not sure this is unusual or a known phenomenon but DO NOT use polyurethane on thin veneers. It will find its way through to the caul or clamps. Hope that saves someone some pain. Larry |
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| Author: | Joe Beaver [ Sat Jan 13, 2007 12:32 pm ] |
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That is some good knowledge to have!!! Just sorry you had to come by it the hard way.
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| Author: | TRein [ Sat Jan 13, 2007 2:21 pm ] |
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I hope I did not lead you astray down the poly path. I always use wax paper between cauls and gluing members, and I always use Baltic birch as cauls, since there are no voids on the surface. It is one of those details that I just do and never think about. Probably one detail I should have mentioned! |
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| Author: | LarryH [ Sat Jan 13, 2007 5:05 pm ] |
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[QUOTE=TRein] I hope I did not lead you astray down the poly path. I always use wax paper between cauls and gluing members, and I always use Baltic birch as cauls, since there are no voids on the surface. It is one of those details that I just do and never think about. Probably one detail I should have mentioned![/QUOTE] Nah, I really don't like poly and should have followed my instincts. Also could not have imagined the swelling that naturally occurs with poly working its way THROUGH the veneer. Even with wax paper my strategy of gluing the veneer first then the fret board would have failed with the nature of the poly. I'll probably try epoxy next time. The part that sucks the worst is my precious weekend's work has to be thrown away and I need to order a new fret board, head plate and veneers, making next weekend the soonest I can do any more work. Humbling Larry |
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| Author: | Serge Poirier [ Sat Jan 13, 2007 7:54 pm ] |
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So sorry to hear that Larry! I don't know much about all the glues that we can use, i used good old carpenter's glue for the same applications you've mentionned and didn't experience anything bad except for the squeeze out which is the same, i hope you can salvage some thing using an exacto blade and a heat source, anyways, i'd say try to separate the glue joints first and see it as a learning opportunity maybe. 
Keep us informed on how you manage please. Serge |
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| Author: | TRein [ Sun Jan 14, 2007 1:58 am ] |
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[QUOTE=LarryH] The part that sucks the worst is my precious weekend's work has to be thrown away and I need to order a new fret board, head plate and veneers, making next weekend the soonest I can do any more work. Larry[/QUOTE] Can you sand or plane the veneer off the bottom of the fretboard and reuse it? |
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| Author: | LarryH [ Sun Jan 14, 2007 2:17 am ] |
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[QUOTE=TRein] [QUOTE=LarryH] The part that sucks the worst is my precious weekend's work has to be thrown away and I need to order a new fret board, head plate and veneers, making next weekend the soonest I can do any more work. Larry[/QUOTE] Can you sand or plane the veneer off the bottom of the fretboard and reuse it?[/QUOTE] It's a new day so I may try that. The head plate though is toast as I tried to sand it and it came out too uneven to use. It's cheap and easy to replace though and actually so is the fret board so it's really just a time and patience thing which are always in short supply around here. |
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| Author: | crazymanmichael [ Sun Jan 14, 2007 9:23 am ] |
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about the only luthier of repute i know of who has anything positive to say about the use of pu glue in out obsession is mario who uses it in laminating cf reinforced braces. to me, many of the attributes of pu glue, and in particular it resistance to releasing, make it by and large unsuitable to our needs. |
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