Sanding the Kerfing - Radius

[buddy225]

I've been doing a lot of reading in the forums and watching John's youtube videos about sanding the kerfing and have a few questions. I don't have a radius dish so i think for this first build I will make a radius sanding stick. It's a stewmac dread kit. Should I use a 15' radius for the back/28' radius for the top, or is it better to trace the actual radius of a back and front brace and use that? Also, should the entire circumference of the top and back have a radius or should certain sections of the top and back remain flat. Thanks for the help as always, Pete

[tippie53]

You can eyeball it for starters .. I think your plan will work so take your time and watch what happens .

[buddy225]

Thank you John. This is one of those areas that I think I'm starting to understand as far as why it's done, just not sure exactly how to do it yet, especially since I haven't done it yet. Your videos are a great help. Question about the radius, should it be applied to the entire front and back, or should certain areas remain sanded flat?

[Ben-Had]

Your going to find different people do things slightly different. I sand the top completely flat and put the radius on the x braces and tone braces (25' radius), the braces above the sound hole are flat. Then I sand a flat slope on the rim from the neck block to the sound hole at a complementary angle to the neck angle (if your neck angle is 88.7 then the complimentary angle is 91.3; 88.7* + 91.3* = 180*) so the slope sanded in is 1.3*.

On the back I sand in a 12' radius.

[buddy225]

So then for the top, you do something like this?

radius.JPG

[tippie53]

that is close enough

[Mitch]

The instructions in the stew Mac kit describe a sanding board that reaches acroos the guitar. it has a 1.5 degree wedge at one end of the stick and sandpaper on the other. It's about 3 inches wide. It seems like a reasonable way to approximate a 1.5 degree bevel along the edge.

My assumption is that after doing the sanding, there may be considerable trial and error to get the top to fit the sides with out any gaps. I.e the ultimate measure of the proper bevel is the top itself.

Is there a reason you are not using the stew Mac sanding stick?

Mitch

[buddy225]

Hi Mitch, I was originally going to make the stewmac sanding stick but after doing some reading on this forum it seems easier to me to cut the radius into a 2 x 4 and attach sandpaper to that, kind of like taking a slice out of a radius dish. Definitely a lot of trial and error here. Which approach would you recommend? Thanks, Pete

[tippie53]

The most accurate is the concave dishes .

[Ben-Had]

So then for the top, you do something like this?

radius.JPG

Yes, except the slope ends at about the top of the sound hole so around where the "3" is. So, sand whole top flat first, then the slope. The slope is also sanded flat the way I do mine. There are several ways to do the slope. Be very accurate not just close, as that is where the action is determined.