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Posted on Jigsaw circle cutting jig fail - now need advice on spiral router bits

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1866 posts in 2794 days

#1 posted 10-23-2018 05:07 AM

Upcut bits leave a clean lower edge and tend to cause fuzzing and chipping on the top surface of the cut. Downcut bits are the opposite. Be careful when using a downcut in a handheld router. They want to lift out of the cut. Upcut pulls down.

Southeast tools sells solid carbide spiral bits that are excellent and priced lower than most competitors. They aren’t as good as a premium bit from Onsrud or Vortex but they’re close enough that the difference only shows when production cutting with a commercial CNC router.

A curious thing about carbide tooling is that breaking most often happens when the feedrate is too slow. Overheating shortens the life and dulls the edge prematurely so it breaks under the load. The faster the feedrate, the cooler the cut. Taking shallow cuts allows for faster feedrates and better chip removal.

I’d recommend cutting about 1/16” outside the desired radius with the jigsaw then cleaning up the cut in a single pass with a sharp 3/4” straight bit. You don’t need chip clearance capabilities for this type of cutting.

-- See my work at and

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