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Routing Circles? Answered

I am trying to CNC circles with pockets. The end result I'm looking for is a circle frame out of plywood about 7 inches in diameter. Cutting out of ¾" ply and trying to make a pocket cut that is ⅜". When I route out the pocket the circle is perfect but when I am cutting the outside paths all the way through the ply I am not getting a perfect circle. I'm using Fusion 360 for the cam and Routing with a Shopbot PRSAlpha. Any advice would be appreciated.

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JON-A-TRONBest Answer (author)2017-05-25

There are a few things that could be causing this.

1. Work Holding: make sure your workpiece is firmly secured to the bed. I'm going to assume you're doing this properly since the inside looks perfect.

2. Jitter: the cutting tool may be too long in relation to its diameter to keep it straight wile cutting. A solution to this would be to use a bigger end mill, maybe 1/2" Ø. The bigger the diameter, the more stable the cut will be.

3. Cutting direction: you might try using Climb instead of Conventional, or vice versa. Sometimes this can affect the smoothness of a curve. See Lesson 4.

4. Multiple depths: If you're trying to cut the contour at full depth, this could be causing the tool to jitter because of the amount of friction. Try cutting the contour using multiple depths (that's in the Passes tab in the cutting settings window) of no more than 1/2 the tool diameter, so 1/4" depths with a 1/2" cutter, for example.

I hope this helps, let me know how it works out!

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