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#31
07-09-2020, 11:36 AM
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FYI - Kenny Hill uses spruce on one side and cedar on the other side (both 6mm/.024" thick). Applies the nomex to the wood, sands it down, then glues the other side to it.
http://www.hillguitar.com/website/ca...doubletop.html
__________________
OM-28 Marquis (2005) Kenny Hill Player (nylon) Gibson AJ (2012) Rogue Resonator (kindling) 
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#32
07-09-2020, 12:05 PM
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Quote:
But then I read this from his article, "First you make the outer skin, then glue on the honeycomb and the other interior structural pieces." So it looks like he builds it up too. I'm not sure why no one does it that way though, a full sheet of wood, full sheet of Nomex, and a full sheet of wood sandwich.?
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#33
07-09-2020, 01:36 PM
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Normally sandwich tops are 'hardened' around the edges and the bridge where the loads are greatest. It might not work well to make up a big sheet of laminate and cut tops out of it.
When I first started experimenting with this construction I got some end-grain balsa sheet. The small individual blocks are held together by a net of string on one side, so that you can handle it as a sheet. The 'clear' side is glued down and the whole thing sanded to thickness before the second skin goes on. In an I-beam the outer flanges are designed to take tension and compression loads, and the web that holds them apart is in shear. The density of the end grain sheet is, of course, the same as that of normal balsa sheet, but side grain balsa has very low shearing strength, where that of the end grain sheet is high. This makes it useful for some applications. The big problem with balsa is that it's denser than Nomex honeycomb, and has more gluing surface. Since we're trying to get the density down, Nomex suggests itself so long as the glue line can hold up. A balsa cored top would most likely give very little weight saving.
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#34
07-09-2020, 02:19 PM
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Alan what kind of glue did you use for the Nomex? I used epoxy but at the time I built mine it was common to use Gorilla Glue or Polyurethane adhesive.
I've always had a horrible time with those foaming up and thought it would fill the Nomex cells.
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#35
07-09-2020, 04:55 PM
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T-88 Structural Adhesive is what most of use. Polyurethane (Gorilla) would defeat the purpose of the lay up and add undesirable internal damping. IME PU glue is horrible to work with.
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#36
07-10-2020, 12:25 PM
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I tried both, but preferred epoxy. Having had many bad experiences with epoxy over the years, and finding some things out about the chemistry, I don't trust the stuff. Polyurethane glue, along with Titebond, is the subject of an anathema pronounced daily by museum curators, or so I'm told. They have another for wood screws.
I wish I could get some small cell paper honeycomb. They make it with large cells for use in packaging, skinned with corrugated cardboard. You could glue paper honeycomb with hide glue. The kevlar stuff is far more heat and moisture resistant, of course, but we don't need that.
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#37
07-10-2020, 01:14 PM
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Quote:
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#38
07-11-2020, 11:42 AM
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Sergai DeJonge made double tops for a while by cutting a lot of little slots in a top, and then skinning it over, but he stopped. Aside from the effort involved in doing this with an X-Acto, I'd expect them to crack along the grain easily.
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#39
07-12-2020, 03:11 PM
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Quote:
And if I remember correctly, when Sergei cut slots they were angled or perpendicular to the grain to avoid splitting but i definitely didn't see them all!
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