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| Lets talk about Double-Tops (McKnight) http://www-.luthiersforum.com/forum/viewtopic.php?f=10102&t=4746 |
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| Author: | John Mayes [ Thu Jan 26, 2006 12:34 pm ] |
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Ok so I did not get a chance to attend the discussion on double-tops at healdsburg, but I'm really interested in doing some experiments with this nomex. Tim M. I know you went to the dicussion. Care to share some insight on application, dimensions, gluing up, ect? |
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| Author: | EBarajas [ Thu Jan 26, 2006 1:49 pm ] |
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They use double tops with steel string guitars? I know my friend Dave Schramm builds double top classicals with nomex and he didn't think they sounded all that different than standard tops. I think now he just builds them if they are requested. I've heard of other builders having top failures even while using the nomex core and these were classicals. |
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| Author: | RussellR [ Thu Jan 26, 2006 8:53 pm ] |
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John Alan Dunwell visits this forum sometimes and he does some great work with double tops, if I remember correctly I think Alan C has some experience in this area. Therefore I can conclude if you want to work with double tops, you need to be called Alan 
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| Author: | rlabbe [ Fri Jan 27, 2006 12:54 am ] |
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John, As far as gluing goes, I got good advice from Randy Reynolds when I asked awhile ago. Basically, you need to use a glue that clings to each little honeycomb and creates a little fillet. There is basically no surface area on the nomex, so you are actually creating a mechanical bond between the sides of the nomex and the top. So you use a thixotropic epoxy, which is just a fancy term for "not runny". You can make it yourself by mixing in a bunch of silica into it, but he recommended just buying T-88 epoxy, which is already mixed to the correct proportion. To coat the honeycomb spread the epoxy on a applicator board using a brayer, then sit the honeycomb in it for 30 seconds or so. Pull off carefully, put it on the top, and vacuum clamp. Run it through a thickness sander to bring it down to size - this is a good test of your glue up. If you failed it'll quickly delaminate from the top. Do the same thing again and glue the other side on. This time you don't have the advantage of sanding to test for delaminations, so you have to get it right. I haven't gotten beyond the testing stage because my glue ups aren't perfect yet, and I don't want to spend more time on this until my solid wood guitars are about as good as I can get them. I remember Alan Carruth mentioning using veneer to do the test glue ups with - this makes sense to me - I wasted a bunch of time thinning down topwood to the appropriate size. I've subsequently played a couple (classical) and wasn't gaga about the sound, though they were fun to play due to the response. So maybe I'm not going to pursue it further. |
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| Author: | Tim McKnight [ Fri Jan 27, 2006 1:18 am ] |
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HI John: Yes I went to the presentation by Charles Fox and Randy Reynolds. I was very impressed byt he shear volume of Randy's guitars as I was seated in the back of the Merlot theater and my ears hurt! As far as tone goes, I don't know enough about classical tone that I can't copmment other than it sounded like a classical guitar only reeeeeelty loud. You can email Randy for the white paper. Read throuygh it and it will tell you all you need to know to get started, I have all of the supplies but I haven't finished my vacuum fixture yet so that is my road block at this point. Dave Borson will re-saw standard tops so you won't have to go thorugh twice as many tops by thinning them to less than 1/2 the normal thickness. Top thicknessing is where I forsee the problems to be. Specifically joining and then sanding them without sanding through them. Randy uses a 16-32 so I know it is possible. He said he went through a LOT of tops at an alarming rate when doing R&D so be porepared for some expense. Nomex is 100 bucks which will do about 3-4 tops if you plan it carefuly. This stuff is very fragile to work with too. He has a list of suppliers in the white paper. I am not much help at this point but plan to have some ready for next years HGF ;) |
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