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I am building a Martin OOO style guitar. This is my third scratch built guitar and most times I feel like I don't know what the hell I'm doing. I just purchased 15 & 28 foot radius dishes for a go bar setup. I lined the dishes with sandpaper for contouring but I'm unsure as to how to use them for this purpose. Are all the braces contoured evenly?

Also, I noticed people using the dishes to contour the back and top rim, but I'm unclear as to the exact way to do this. Do most builders use the dish for the rim contouring? Is it necessary? I don't know why, but I'm confused on how use the dish for this purpose.

Any help for my hopeless cause would be appreciated.

Thanks, Mark

I think you can find reams of discussion on this at MIMF, along with some photos and instructions on how to motorize the dish for sanding.

_________________
Howard Klepper
http://www.klepperguitars.com

When all else fails, clean the shop.

Hi Mark,

I am in the process of doing this on my first build. I would not waste anybodies time giving technical advice since I am a beginner, but I would highly recommend you buy/view Robbie O'briens DVD and/or John Mayes "Rims" DVD - they are invaluable and explain the process in a very clear and concise way.

Glenn

Howard's right, you can find a lot of information on both the MIMF and in the archives here with
a little searching. The quick answer to your questions is that you can use the dish to contour
both your braces and the rims. In both cases, it's easiest to remove most of the material with
a quicker method- plane or saw usually, then do the finish work in the dish. The rims have a lot
of material to remove at the top bout and at the heel- you are asking them to take the shape of
the dish. Because there is so much to remove- especially on the bottom, where you have the
greatest radius, and also the taper in body depth from top to bottom, it is much easier to
mark the contour on the unbent sides, cut most of the material away,then bend them. The
process is too long to describe here, but it's been covered well on both forums. I also
recommend the DVD's for beginning builders. You can find the information with searches i
f you want, but there are a lot of different small points to dig out, and the DVD's cover
it all in logical fashion.

_________________
Gene

Politicians and diapers must be changed often, and for the same reason- Mark Twain

Mark here is the basic idea. There are many variations too including a motorized dish sanding set-up but the basic idea is to sand the radiuses that you want, 15 and 28' respectively, into the braces for the top and back and the rim for the top and back.

Be sure to use the correct dish when working on the back or top too.

Sand the braces in the dish and this will sand the radius into the braces. Place the rim in the dish prior to installing the kerfed linings and sand the back and top radiuses into the rim by moving the rim, in the mold, pulling one side toward you and pushing the other side away. This is much like the motion of steering a car.

Imagine an imaginary stake going right through the center of the rim and this is what you want to rotate the rim around in the dish.

You can either set the rim in a dish and do this sanding the bottom side, this is what I do, or place the dish upside down on the rim and move the dish. If you place the dish on top use the other dish to hold the bottom of the rim in place. It also helps to place something under the dish that comes into contact with the bench to keep it from moving.

I sand the rim first without the kerfed linings and then, once sanded, I install the kerfed linings slightly proud of the edge of the radiused rim and sand in the dish again now adding the dish's radius to the kerfed linings and making the kerfed lings flush with the sides.

A friend of mine calls it "driving the bus".

It serves two purposes for me -- it sands the kerfed lining down to the level of the guitar side and it puts a tiny radius onto the top of the lining so it matches up with the radius of the top or back.

_________________
53% of all statistics are made up on the spot
http://driftwoodguitars.blogspot.com/

Thanks everyone, you have been extremely helpful and the explanations are very good. I think I understand it now.

Mark

Uh, the dish is spherical. It really doesn't matter if you rotate it, move back and forth, side to side, or any combination thereof. Certainly when it comes to the rims. I tend to do a bit of everything to spread the sandpaper wear evenly, back and forth only once I've got full contact.

I also tend to move the rims on the dish, and not the other way around. My molds are three layers of 22mm MDF, so they're fairly heavy. I don't pre-shape my sides before bending, but rather prop the bent sides up in the dish to the appropriate taper and trace the rough size on there. Cut and plane down to the line, finish on the dish. Colin S did a pic tutorial of this 'marking' system which he uses to pre-shape the sides, but can just as easily be used to shape the sides once they're clamped.

Many ways to skin this one.