MIMF

I recently read a post (I can't for the life of me find it now) where a luthier described building a double top with 1mm spruce/1mm nomex/1mm spruce. As far as I can find, no one sells 1mm thick Nomex.

Can Nomex honeycomb be thicknessed? Can you pass it through a drum sander? How about sanding it while already bonded to one skin? I'm thinking about perhaps hitting it with a sander to strategically thin in places (like a recurve). Is Nomex at all workable in that way, or are you stuck with the 1.5 and 2mm thickness LMI sells?

If not, is there another source for the Nomex? Where would one find thin honeycomb nomex that is only 1mm thick?

Thanks!

I have read about someone thicknessing nomex on a thickness sander. It may have been an article by Randy Roberts.

From the little experience I have with the stuff, I think you need to glue it to something first. I glued it to one skin, thicknessed that, and then glued on the other skin. The Nomex by itself doesn't hold still while you sand it.

Everything I know about Nomex I just learned ten minutes ago by watching the videos on LMI's site here: http://www.lmii.com/products/mostly-woo ... wood/nomex

They show in detail how one builder makes his double tops, including the dimensions he's using on each layer. Interesting stuff.

Thank you Alan. That is what I what I was hoping for, someone with more guts than me who had actually tried

I was dreaming of experimenting with arched shapes, but my instinct was that if 1.5mm was stiff enough for a flat top with no bracing, it would be too stiff arched. As I mentioned, I read one luthier who claimed to use a 1mm/1mm/1mm laminate. It made me think that I could experiment with the thickness of the Nomex. If I have to glue it to a flat plate first to thickness, that is probably a no go.

I try to learn from others before I just jump in and make mistakes, but I will probably just have to give it a go and see what happens. I am still in the early states of experimenting with a vacuum bag and laminates, so this may be a while off. But like a lot of us on these boards, my dreams are always way ahead of my actual skill set

Be aware that Nomex had a really high Poisson's ratio: when bent so any significant curve in one direction it wants to bend the opposite way in the other, assuming a saddle shape. It will resist any effort to form an arch much more curved than the usual 14' or so dome. If you're going to make an arched top I would think you'd need to get a thick enough piece to shape into the arch, glue on one skin, and thickness from the other side. Not having tried it, I could well be wrong on this, of course, You might get away with using narrow strips of Nomex, of course.

I hadn't thought of that possibility. If I understand you correctly, you are suggesting getting a 1" thick piece of Nomex honeycomb and carving and arch into it? I suppose there is a reason this has rarely been done. Nomex honeycomb is not necessarily cheap; I hesitate to think what 1" thick material would cost. Even if it wasn't expensive, it seems you would have to support one side first, carve the interior, laminate the interior with a skin, then carve the exterior skin off, then re-laminate a curved skin. Really doesn't seem practical.

Working with strips is another idea, of course. Having long bilateral sound holes seem almost to suggest such an arrangement. I suppose there is nothing to be done but try!

There is in fact someone making archtops as you suggest, without resorting to Alan's method. I forget who he is and where I saw it, but it's out there, so google should find it.

Mario Proulx wrote:There is in fact someone making archtops as you suggest, without resorting to Alan's method. I forget who he is and where I saw it, [...]

Steve Andersen. As one can appreciate in this video his double tops are only slightly domed, and with no recurve.
Someone else actually forced the Nomex layer into a more archtop-like shape between two thin spruce layers, and ended up with a cracked top due to the introduced high tensions, you should find it with google's help.

Thank you for the link to the video. It was certainly helpful. I don't know if Steve Anderson is one to share his technique, but I will try emailing him. It is hard to tell what his end shape is from the video. Perhaps his tops don't need a recurve to have good tone and projection. Also, his arch seems very shallow. When he lays the finished top on a flat surface it doesn't seem to arch too much more than a 15' back might. Maybe arching for a double top is solving a problem that doesn't exist. Perhaps the double tops are strong enough to withstand long f-holes and the down force of a floating bridge without the strength benefits of an arch.

Looks like I'll have to do some experimenting. I don't suppose anyone knows of a source for 1.5-2.0mm Nomex that is less expensive than LMI?

http://www.acp-composites.com/honeycomb.pdf

Hello Randolph,

The above link is for a .06" thick sheet. It might do what you want.

Mike

Thanks Mike! That is definitely a better price by about half than LMI. That will make it possible to build three or four experimental tops without breaking the bank.

PS: My little CNC machine has been rebuilt and is running well. I'll send you some pictures over the weekend. Thanks for your help and encouragement!

Glad to be of help Randolph.......and btw, we are still gonna do the two arch tops. I am attempting to secure a very real cnc machine! CR Onsroud, twin 3.5X4 tables each with a vacuum, feed rates to 3000+ ipm.....and rigid like you can believe. If all goes well, I will have it in my shop by end of summer.

Yes, please send me photos and stay in touch!

Mike