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what are the top and back radius on a Martin D28 Dreadnaught? I was I check myself before I go any farther.

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Mistakes are mandatory-learning from them is optional. http://www.opensourceluthiersupply.com

28' top, 20' back. Modern ones anyway.

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Eschew obfuscation, espouse elucidation.

I think you may be right on that Todd. I'm recalling that info from last time I
cared much about what Martin did, which was at least 10 years ago.

But really, now that you mention it 25' does sound right for the backs.

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Eschew obfuscation, espouse elucidation.

Todd has it right. 28/25 for D and 28/20 for smaller.

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Don Atwood
Arlington, VA

 So that is the size radius discs I need for this projects? I want to use the discs for sanding the kerfing and making the braces as well. Is there an easier way?

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Mistakes are mandatory-learning from them is optional. http://www.opensourceluthiersupply.com

Bill, you can use a sanding board for the kerfing but the dishes are the easiest way for me. Look at the StewMac directions for building a sanding board. StewMac directions.

For the braces you can make a template and radius using a router with a pattern bit or plane or you can use the Brace Maker sold by Luthier Suppliers. Brace Maker.

If you plan to build more than 1 guitar the investment in dishes is well worth it. They are also good tools to glue the braces to the top/back and also the top/backs to the shell using a gobar deck.

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Don Atwood
Arlington, VA

Hey guys -

Is there a rule of thumb about how to apply an appropriate radius to designs.

I made myself a 15' and 30' dish for my last build (wasn't that hard, just took some math, some plywood, a router, some earplugs, a couple of hours' time, and a good shower afterwards).  The last build was an OM; now I'm planning something bigger (20" length and 16.25" width), but was planning on using the dishes I have.  Would different radii be more appropriate for a larger guitar?  How do you determine this?

Because, honestly, although the dishes weren't hard to make, I'd like to avoid the complaining from the wife about the noise...

When I asked that question here a few years ago, I was told as a very general rule that the more dome the more projection, and the flatter the dome the more warmth.

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Don Atwood
Arlington, VA