Official Luthiers Forum!

I am in the market for radius dishes and I am a bit confused, or I guess I should say uneducated about them. Stew Mac sells the following:

15-foot radius for Martin backs
20-foot radius for modern guitar backs
28-foot radius for modern guitar soundboards
40-foot radius for Martin soundboards

I am curious why the change in radius for modern guitar versus Martin. Does this change in radius really make a difference in tone and structural integrity? I am planning on building my first guitars closely based on Martin guitars so should I go ahead and get the Martin radii or is it better to get the modern radii? Any suggestions on a few all around radii to get? These things are expenses so I'm hoping I can get just one for the top and one for the back. Thanks for any advice.

Either way. I guess if wanting to stay true to Martin and that is their standard then do that. My dishes range from 60ft to 24 ft on the top and 30 ft to 15 on the back. You can have what you want. If just starting then suggest stay with those by Stew Mac No reason for that other than they are proven for quality sound over the years. Once you have done some guitars and want to check out others then go for it.

For the dish with smaller radius such as 25' which I have been using, I found serious issue with gaps under the fretboard unless a very high neck angle is used. I had to shim the fingerboard in order to make the gap disappear.

So that's a reason for me to use a flatter radius for the top.

_________________
Cat-gut strings are made from kitten guts, stretched out to near breaking point and then hardened with grue saliva. As a result these give a feeling of Pain and anguish whenever played, and often end up playing themselves backwards as part of satanic rituals.

Typhoon Guitars
http://www.typhoon-guitars.com

Todd, do you flatten the rim north of the waist to match the flatter upper bout or do you just sand the whole rim to 28' and get what you want from the flatter brace?

_________________
Bryan Bear PMoMC

Take care of your feet, and your feet will take care of you.

Martin backs are not 15'. Closer to 20'

The radius has little to do with tone. I culled my disk inventory to 28 for top and 15 for all backs. the key for the top is to match the neck angle so you have a flat and true fretboard plane with about 1/2 inch string height at the top .

_________________
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

You got me on that one Todd. Are you saying that the back on the D and M are a 25' radius? And going how far back in time? Especially since their tops are so flat also. I use 20' for my 000/OMs. Wish John Arnold would add on this as I remember he and Willie Henkes talked about a compound radius on the backs of older Martins. Meaning that it was different longitudally than across the back and they were braced up in fixtures rather than dishes. Somewhere on the UMGF there will be a thread showing pix of the fixtures and more discussion.

Tim

I'm about to use the Grellier plans to build an OM. The plans have a 25' radius on top. If I used a 28' radius would I have to change the bracing at all? I could then use Todd's method of the 60' UTB.

_________________
We are all in the gutter but some of us are looking at guitars.

No need to change the bracing plan based on a 3 foot difference (which is almost nothing over the span of a brace) in radius.

backs on Martin dreds start at 20 foot radius and 000 at 15. Also a note is once they are glued they tend to change a bit from RH. As for the top there is a slight radius and a 1 1/2 degree incorporated to the top. As a repair center for Martin I was invited to go to the CF Martin repair summit last year and this is the equipment that they use .
I was allowed pictures and to study this . It is quite the machine. I wish I had one.

_________________
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

^^^ Nice!!!!
Beats the crap out of "driving the bus", right John?

Thanks guys. I think I will go with a 28' for the top and 15' for the back for now. Has anyone bough radius dishes from Luthier Suppliers? http://www.luthiersuppliers.com/products/p4.html It seems like their dishes are well made and fairly priced.

John, are those holding fixtures pneumatically actuated? That's pretty cool, although only making a couple guitars a year think I can still hold mine by hand.

Tim

there are pneumatic cylinders there so I think so. It is a nice chunk of engineering

_________________
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 just ordered a set yesterday Good stuff. Tracy made my first few as well.