Official Luthiers Forum!

Here are some pics from the double top masterclass held at Red Rocks Community College this weekend. We made 14 double tops. Alan Dunwell gave the class and it was very interesting to say the least. He even discussed Chladni patterns on a double top. Every student left with a double top ready to use on their own guitar. I can hardly wait to see and hear the results from the class over the next few months.

Very interesting Robbie. One of these days I've got a top or two that's not very stiff that I'll try this on. Thanks for the pics!

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Bobby Masten

That's very cool. Jealous here.

Will there be enough parallel build activity to really tell if the double top makes a difference?

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Jim Kirby
kirby@udel.edu

Jim, next semester I expect to have around 10 people building with double tops and around 20 at least building normal tops. We should have a real basis for comparison.

Cool class, Robbie. I always enjoy your offerings! Would love to try a double top sometime. Doesn't look like Nomex...have you ever used that? Beth

From the pics, it sure looks like Nomex.

Greg

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Gwaltney Guitars

Thanks.
It is indeed Nomex

I had fun! (I'm the guy with thebig brown beard.....)

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Old growth, shmold growth!

That looks like quite a class. I attended the Chlandni tuning lecture given by Mark Blanchard at the last Healdsburg show. Interesting stuff.

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"Preoccupation with an effect gives it power and enhances the error"
from "Your Owner's Manual" by Burt Hotchkiss.

As Robbie mentioned, it was a fun class. And I have to reiterate what I told the folks in the class, they were an outstanding group. They worked long hours and helped each other out with the assembly and clean up and everything. Just a great group to work with. Kudos to the clan!

Alan D.

I think there might be a market to sell double top blanks, especially for people like me who are too allergic to uncured epoxy to laminate them.

I had the pleasure of taking the class, and I can say it was first rate! Being the first class, there were a couple of bugs to work out, but Alan and Robbie soldiered on right through them.

Not only was being there with Alan to walk us through the process a great benefit, but we also got his decade plus experience with double tops, and the pros and cons of different techniques and materials. Also, the crew and facilities at RRCC were fantastic. Well done!

PS Robbie my memory of my traditional top weight was off by about 100g, should have been ~125g not 225, oops.

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Matt Jacobs

"Don't tase me bro"

I thought the same thing and even emailed Stew Mac about it and asked here. The general consensus is that luthiers will want to do it them selves to gain better control. But I still think there could be a market for it too. You can use Gorilla Glue instead of epoxy but just be real careful of the amount so it doesn't foam up and fill in the honeycomb.

The solution to uncured epoxy is to use what many use with great success and that's PU glue.

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Waddy

Photobucket Build Album Library

Sound Clips of most of my guitars

When it come to double tops and glue, we need to be careful. I tried to emphasize this in the class. We really don't want to have double tops out there that fail or otherwise are less than they could be.

Polyurethane glues such as Gorilla Glue and so on may work just fine but one needs to do their own testing first. Before building with the glue I use I first made various test strips of spruce and Nomex, using less and less glue for each one. I then ran them through the drum sander to see which ones exploded. That gave me a measurement for the amount of glue per square inch that I need for the type and style of building that I do. What I do may not work for someone else, each person needs to do some testing for their own conditions. Nuff said.

Alan D.

Do you spread the glue on the nomex or on the top?

One of the students that attended the class asked me last night if I knew of anyone that might be interested in purchasing his double top made in the class. I think it is an OM model and he wants to build a classical model but not in the near future. If anyone is interested PM me and I can give you his contact info.

The method that I use is to spread some epoxy out on some parchment paper then dip the Nomex in that, just basically press it on top and move it around a bit. Then peal the Nomex off and lay it on the soundboard appropriately. All you want is to glue the edge of the Nomex to the spruce being very careful not to fill in the honeycomb.

Like jfmckenna does, the standard way is to roll out some glue onto some sort of platen and then press the Nomex into that. The thickness of the glue layer determines the amount of glue picked up. There are some tricks to doing this and the kind of glue is important to not getting too much glue and keeping it in place once the Nomex is placed on the skin.

Alan D.

Many thanks for that info Filippo. If Randy is using it then I'm sure it is great but I'll bet you dollars to donuts he did a bunch of testing first too. I know he did back when he was using epoxy because that is where I initially got my data when I started. I haven't talked to Randy recently so clearly we need to compare notes again. Randy makes absolutely top notch instruments and if I recall right from the one you had at the Colorado Luthier's get together at his house, so do you.

Laters,
Alan D.

As far as the safety thing is concerned, PU glue on wet skin is highly carcinogenic. I have that from a glue scientist who worked for one of the large chemical companies. But I have only heard it the once.

For the most part PU glues make me cringe. It has its place, but I wouldn't personally let any of that stuff near my guitar. But having said that, I have heard of a lot of builders using PU, including some prominent innovators, so it must be OK, at least for now. I sure wouldn't want to fly in a nomex aircraft held together with PU.

My real reason for posting was to draw attention to this stuff:

http://www.ecopoxysystems.com/products.html

I use WEST, but this stuff is apparently aircraft usable, and if one was worried about sensitization, it would be worth whatever it costs to get it, particularly given the amount of any of this stuff we use. One can adjust any flow problems with additives.

As I understand ecoepoxy cures out with a higher modulus of elasticity. This is not something I would be looking for in a glue used on a guitar top...fish glue may be an option, roll on to a flat base and transfer via contact as above.

Cheers

Kim

I just finished my first DT guitar too. I used epoxy because I don't want the PU glue to foam up and fill in the voids. I just don't have confidence in using it yet. But I have used PU on furniture projects and the stuff is incredibly strong.