Official Luthiers Forum!

Ok this is probably one of them threads where everyone shakes their he's because it's been answered a million times but I can't seem to find a direct answer.
This will be my first time using the Simpson neck angle jig and I was wondering is it better to have a flat area above the soundhole when using this jig? On my first build I went Cumpiano method and on number two I had the entire soundboard radiused because the fretboard was raised and did not glue directly to the soundboard. On this build I'm going with the more standard approach of using a 28' hollow form and then going to glue the fretboard extension directly to the soundboard. I'll be fitting it all up with the Simpson jig an was thinking using a flat UTB to flatten out the area above the soundhole would probably be the best approach. I jus wanted to get some advise from the pros before I started gluing. Thanks a million.

So you are saying make the UTB curved with the rest of the top? But shim the fretboard? Sorry for the confusion my brain isn't wanting to work right today.

It's always a good idea to have the neck coplanar with the soundboard in the upper bout, too, so that you don't have to either bend the fretboard or wedge it somehow. And with the neck coplanar, you have to deliver the correct string height above the soundboard and the target action at the 12th fret. So what actually sets the "neck angle" is the longitudinal curvature of the upper bout and how that plane projects over the saddle position. With the neck and upper bout coplanar, you then match the angle of the heel to the sides (using a Woolson style fixture if you want). As it turns out, for the "normal" range of top dish radius (~28' to ~33') flattening the radius of the UTB to ~60' gives the correct longitudinal curvature of the upper bout to give you the correct string height above the soundboard at the saddle position. I do it by planing a flat on the UTB, which is effectively much the same thing as using a 60' radius brace as Todd suggests and, of course, NOT gluing the UTB on in the standard radius top dish.

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Trevor Gore, Luthier. Australian hand made acoustic guitars, classical guitars; custom guitar design and build; guitar design instruction.

http://www.goreguitars.com.au

Thanks Trevor! That really clears things up. That is precisely the info I was looking for. I'll flatten the upper bout and see how it goes.

Thanks Todd! Your second message helped clear it up for me. My brain is just shot today. I think you need to move to TN so you will be close when I need ya

Zeke , if you need help with the simpson jig call or e mail jon simpson for an explanation.Or maybe you/ve already figured it out?

I think I've got it figured out. I've read the instructions several times and feel good about it. We'll see how it goes. Thanks for the tip though. I'll shoot him an email if I get into trouble.

Sometimes a picture helps, what Trevor is talking about is when the top has a the correct radius the fretboard should be coplanar to the top giving the proper height at the saddle, in this case its a 12 fret model...one of the nice things about the methods he uses with carbon fiber ,IMO, is that the epoxied braces when glued in using a radius dish lock in the top radius , the upper transverse brace is radiused cross grain , in my case to 70' diameter , using a caul and a brace shaped using a jig ...

I hope these pics post ok......

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MK5acoustics.com