Troubleshooting Swirl Marks from CNC Bit

      Pros suggest several flaws that could be causing swirl marks created by a tool tip in flat areas. March 6, 2006

I have a Techno-Isel CNC router and I cut patterns in wood and ren board. When I cut flat areas, I get swirled tool marks. Not sure where to begin to determine the problem. Vibration? Spindle and/or table need leveling? Fixturing? Any advice will be appreciated.

Forum Responses
(CNC Forum)
From contributor P:
Could you be a bit more specific? What type of spindle (Porter-Cable, Perske, etc.), tooling, feeds, speeds, fixturing, etc?

From contributor V:
1. RPM is too slow for the feed rate.
2. The tips of the tool are different heights.
3. One tip of the tool is damaged.

From contributor G:
Try the Onsrude 66-300 series. They are made for bottom surfacing applications. They are up-spirals with the tips rounded off. I've had good experience with them.

From contributor B:
Check to see that your spindle is square. If the head assembly is not square, the tool will cut with one edge/tip and leave swirl marks. To check squareness/spindle sweep, mount a dial indicator to the spindle so it will swing about a 24" diameter circle, bring the indicator down to the table and slowly spin the indicator 360 degrees; you should not see much more than .002 total. More than that and you probably need the head squared up.

From contributor E:
I am assuming the swirl marks are on the bottom of the cut. It could be from a variety of things. Bottom clearance or lack of on the tool. Too fast rpm's. Chips are being recut. And like the other gentlemen mentioned, spindle can be off.

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