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I see that there are various radi people use: 25', 40' for the top, 15' and up for the back.

What are the advantages of one over the other? I'm partricularly facsinated by the 25' - 40' spread for the top.
How the heck did those radi originate?

Thanks,

Jim

I have no idea what acounts for the spread but it goes way beyone 40' to a flat top for some builders like Olson and Ryan. The flat tops are what fasinate me, I find it hard to believe that you need to build with a dome if those builders feel you don't need one. Of course, there are a lot of folks, and a lot of guitars, on the other side of this issue.

John

The radius will equate to the neck angle you are using. 28 is normal for a 1 1/2 degree 25 for a 2 degree . check out this link to see how this is figured in to get the side geometry right .http://www.youtube.com/watch?v=QYHPCeVRUA4

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John Hall
blues creek guitars
Authorized CF Martin Repair
Co President of ASIA
You Don't know what you don't know until you know it

Maybe with a flat top you don't have to bother tilting back the neck at all? If that works, it's a lot simpler to build, both when bracing the top and working the geometry...

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Build log

Hmm. I never thought of that. If I did my quick calculation correctly then it would work out about right. A zero degree neck angle would work for a flat top. The E string would be about .52" off the deck at the bridge. My calculation assumes that the bridge doesn't pull up with string tension and the neck stays flat. From what I read, the flat tops do pull up, in fact, one guy who owned one was convinced that it wasn't built flat until he talked to the builder. All very interesting.

What do flat top builders do about neck angle?

John

One of the most important reasons for using a radius is not only for structure but looseness or stiffness of the top or back plate. This directly influences your tone. The model dimensions of your guitar and the tone you are trying to achieve make it imperative that you understand the direct influence a radius will have on your guitar. Choose your radius first and then design your guitar to make that radius work. i.e neck angle.

Actually , you still do. In most cases you are looking for the string height to be about 1/2 inch in front of the bridge . With the action at 7/32 at the 12th fret you will need to have a bit of an angle to get all the lines of the neck angle , relief and string line . Most build with a slight radius as the doming can ad strength to the top and allow movement in RH changes.

_________________
John Hall
blues creek guitars
Authorized CF Martin Repair
Co President of ASIA
You Don't know what you don't know until you know it

I'm using about 1/2 degree or less with a flat top. Will be trying a cylindrical arch on the next 6 though.

I think John may have meant 7/64" action at the 12th fret?

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Gwaltney Guitars

yes I go this mixed it is 7/64

_________________
John Hall
blues creek guitars
Authorized CF Martin Repair
Co President of ASIA
You Don't know what you don't know until you know it

What is the "mystery" of "Flat" flat tops? They are some of the easiest tops to build... you just build on a flat workboard and Viola... Flat top! Sanding the rims is cake too... just sand on a Flat workboard and Boom... Top Rim sanding is done!

Then routing for the top bindings is a Snap -- no weird arches to mess up the router cuts..

Neck setting was easy enough too -- I built the neck flat to the body. No problems what so ever setting up the action.

That guitar was a small body, and came out sounding warm and wonderful. I think part of this was the Flat top.

Thanks
John

For me most of the mystery is about "why" some of the very experienced builders build with flat tops. It seems that there is a very good reason for building an arch into the plates yet if these builders can make great guitars that stand the test of time without an arch then the arch may not be as important as its common usage would suggest.

I also wonder if Olson and Ryan start out with top wood that is drier than most start out with.

John

Add Ervin Somogyi to your list as well...

Sure, there are great reasons to build arch/domed/curved tops on Flat top guitars... but there are also very good reasons to try out Flat tops on steel string guitars too.

I get a feeling that the Arch came to us as a hold over from the old Gut string days -- Those guitars have very little treble to start with... and I have a feeling that the Arch really helps tighten things up with the lighter soundboards so they don't sound too "Plunky" as they open up.... especially when you consider that those old Hand Made Gut strings could cost more than the Guitar -- so they seldom got replaced... This may explain part of the weird sound of those old European guitars when folks string them up with nice fresh modern strings.... They may have been designed to sound right with old "Dead" strings on them.

On our steel string guitars, we can easily end up with way too much bright treble... so it may be preferable to do something in the design to kinda "Warm things up" a bit... but still leave enough wood so that a bump on the top doesn't knock a hole in the guitar.... and the "Flat" top does this pretty well.

What I will say is give it a shot. Build one out of leftover wood... and you won't be out much but time. I built 1 guitar this way. I will soon be done with the 2nd curved top and then I am going back to a "Flat" top for the next one.

Thanks

John