Tight radius when pattern routing...

[Michael Donahue]

I'm actually working on an electric bass guitar but this problem has come up in a few other spots. Sometimes I need to route from a pattern with areas needing a tighter radius than my bearing bits can handle. The picture is a good example, where the corners are about a 1/8" in. radius and my bit has a 1/4" radius. How can you route something this tight? Thanks for the info.

[Dale Lesak]

you can go with a bit with a pilot bushing. they make some with a brass bushing. I don't know for sure just how small they go. Dremel makes some router bits for their tools. Plus someone also makes them in carbide 1/8 shank

[Michael Donahue]

you can go with a bit with a pilot bushing. they make some with a brass bushing. I don't know for sure just how small they go. Dremel makes some router bits for their tools. Plus someone also makes them in carbide 1/8 shank

I need a bit with a top bushing though.

[glenn bradley]

I know this is only one example but if it is an 1/8" radius; use a 1/4" bit and make your template larger according to your top bearing. If I want to make a 1/4" half circle as in the pickup areas of your example and I have a 1/2" top bearing, I make a 1/4" radius in my template. the bearing seats right into the half circle leaving an 1/8" radius half circle (half of a 1/4" bit). I wouldn't want to make pickup cutouts with an 1/8" shafted bit.

I prefer flush trimming when using patterns but this is not always possible (like in your example). Draw your template to size then draw a line outside of the pattern that matches the offset of your bearing to cutting edge measurement. Now cut to this line for the template. If you look at patterns or templates that are designed for collar guided bits, you will see what I am driving at. For example, a door hinge mortise template is larger that the resulting cutout by the offset of the collar to the bit.

[Doug Shepard]

I think I'd use a brad point or forstner bit in the drill press and drill out the tight radii first before switching to the router.

[Charles Lent]

Use a forstner bit to drill out these places before using the router. Then make your router pattern without these holes so the router won't try to go into them. This will keep the edges of the holes sharp and crisp. Not everything has to be done with the same tool, and there are several ways to accomplish almost everything in woodworking.

Charley

[Jim Becker]

How about a guide bushing in the router base with a smaller diameter cutter. These generally can get much smaller than a bearing guided bit. This is exactly how inlay sets are constructed.

[Lee Schierer]

How about a guide bushing in the router base with a smaller diameter cutter. These generally can get much smaller than a bearing guided bit. This is exactly how inlay sets are constructed.
I agree with Jim, the inlay template bits are 1/8" dia on the cutter and will easily do small radius cuts on inside corners. This sit has them down to smaller diameters small diameter bits (http://www.stewmac.com/shop/Tools/Dremel_rotary_tools,_attachments/Carbide_Downcut_Inlay_Router_Bits.html) but I can't say how well they really work having broken more than one 1/8" bit in my router.

[Tim Put]

You could route the majority of material with your half-inch template bit, and then clean up the corners with a quarter-inch bit (eigth-inch radius) running the shank against the template. If you use a slower speed, and take light short passes with little pressure you can avoid burning the template, bit or the body.

[Jim Becker]

Lee, I wouldn't actually use the inlay kits for this because they are not designed for the stress of machining thicker material, but concept holds true with a guide bushing and a straight/spiral cutter appropriate for the job.