Can't cut circles

OK, I’m missing something… this isn’t the “it cuts an oblong” issue - circles, when I can get one to cut, are pretty round, but most of the time, the left-hand side is messed up.

Most of the circles seem to start at about the 2 o’clock position. Cuts counterclockwise (maybe that’s my issue? it’s just the default), when it gets to about 10 o’clock, it starts “riding up” off the board and slipping, making a ragged, nearly vertical cut (with jerks and jogs) until about 8 o’clock, then we’re back to cutting and all just fine.

Only ideas I have had are:

  1. I need more tilt, I’m too vertical on my work surface
  2. the bit I’m using isn’t really “right” for this - just a 1/4" slot cut bit, but it is what I had handy, and otherwise cuts great in this light stuff
  3. I need to go the other direction due to router rotation or something

Anybody have suggestions which to try and/or something else to attack this?


I think the bit might be your issue. Try a 1/4" up-cut bit if you have one. A dull bit might add to the issue.
The CCW direction seems proper.
Not sure about your slope - I’m using about 16 degrees. Many cellphones will measure slope for you.
Are the chains running smoothly on the sprockets?
Adding more weight to the sled might make a difference, that 10-to-8 part of the circle relies a lot on the weight of the sled for motive force.

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can you post a short video showing the problem happening?

where in the work area are you cutting? near the center? near one side?

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If the router is climbing the cut, you might need more weight. A bit with less friction would be good too. (A spiral cutting surface rather than a straight one.)


An upcut router bit will pull the router into the work while cutting adding more downforce to help hold it in place

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As a simple test you could also try lowering the cut speed, if slower motion results in better cuts then it’s almost certainly not software - check the things already mentioned (bit, sled weight). Or maybe try putting your hand on the router and giving it some positive “down” pressure while it cuts? If this improves things then add weight (and probably use an upcut bit)…

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Thanks all… I’m getting an uncut bit… I suspect that will make the biggest difference.

Tried the hand on the router trick… maybe helped a little, but not a ton.

I’m going to measure my “tilt” when I get a second and may adjust that - easy change with my setup and can see what happens.


Just in case anybody ever searches and finds this or something… life intruded (I’m buying a house and fixing to move it seems… hadn’t really planned on that, but… all good, but a lot of work).

Anyhow, I did get a couple of the Maslow upcut bits and it seems to have fixed this issue… just did a couple of cuts and circles all seemed fine.

So, lesson learned - use the right bit :slight_smile:


is 16 degrees the recommended slope?
when i took the existing drawings and
put into cad it came out to 10 degrees.

would love to know what works best.

Between 5 and 10 degrees :ok_hand:t3:

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we don’t really know what works best, we haven’t had enough experimentation.

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glad that we have the unistrut frame made up.
should allow us to change slope easily!