Tool path wanders while cutting wood

Hey Guys.

So i’ve been doing alot of MDF cutting and my toolpath would eventually wander erratically.
usually on the second pass it loses itself and goes off direction in the X plane.
I have tried to tighten the belt on the X but it doesn’t seem to help after awhile

Right now these are my settings.
i’m using a 2 flute 1/4" bit from mcmaster
cutting rate 20ipm
plunge is 10ipm
depth of cut is 0.1"
my dewalt 611 at 4
i’m also creating toolpaths with rhino cam.

any thoughts on why my tool path won’t stay consistent? I have a feeling its a physical problem. maybe i’m taking off too much material for a belt system? my friends cnc at work cuts at 80ipm with the same depth no problem…


How far off path is it going? A few [edit: tens of thousandths, not ten thousanths] ten of thousandths, or much more?

Have you checked the tightness of the guide wheels against the vrails? (Shouldn’t be tight per se, but should not allow the wheel or carriage to wiggle).

Have you checked the set screws on the stepper gears? Those have consistently given others trouble… verify that one of the set screws is on the flat spot of the stepper motor shaft, and that all set screws are tight.

Your feeds and speeds look good… conservative even. If you haven’t already, consult the chart here:

EDIT: moved to:

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it basically gets stuck and the bit makes squiggles.
the rails are fine, and the set up dose not wiggle really.
Checking the set screw seems like a good idea. i’ll have to try that one tomorrow.
it is only the X direction that gives me problems. the Y and Z have been very consistent.

I too thought my feed and speeds were conservatives! But i can’t seem to get a consistent cut.
based on the chart i can run my 1/4" at 80 and cut .3? has any one achieved that? it worries me alittle bit…

thanks for responding.

Should be mechanical — please check the usual suspects:

Also, slotting is hard, and MDF dust will tend to expand after cutting — add geometry and cut as a pocket so as to allow chip clearing. If you’re not using dust collection, do so — the adhesives and other chemicals added to MDF are very bad health-wise.

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If you search the forum for “set screws” or similar terms, you should find other threads describing a similar problem to yours, along with discussions of the solution. I suspect that’s your problem, but I’m curious to hear either way what you find.


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Interesting point about MDF dust potentially clogging the slot, Will, I hadn’t thought about that. Really good suggestions.

Is your bit an up-cut, Peter?

by up cut you mean spiral? Yes.

They’re both spiraled, but up cut pulls your chips up, out of the slot, and down pushes it down.
They look like right and left handed bits, but both actually cut in the right handed directions.
Down cutters are good for not lifting your part off of the table.

Not deep enough to clog.

Oh yeah :slight_smile: It’s amazing to me too.

That sounds like inch being run as metric, but not with this in the mix

Must be mechanical if Y and Z move correctly.
The squiggles are probably the set screw bumping the flat, barely moving it every bump.

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This has happened to me. One time it was a loose drive pulley. The other time there was an intermittent connection in one of the motor extension cable pins. They both showed up when jogging manually which made it easier to troubleshoot.

As far as feeds and speeds for MDF… 0.25" DOC and 120 ipm will work with a sharp bit. I tend to push my machine hard and the only time it’s really caused issues is if I try to plunge too fast. I always use ramp plunge cuts to avoid missing steps in the z axis.


Ok finally had time to check the machine.
and yes… i’m missing a set screw… where can i find a replacement?

The pulley set screws are a standard part, M3 ~4.75mm o.a.l. which any decent hardware store should have in stock — if your machine is still under warranty though, contact and we’ll send a couple.

In the meanwhile, your machine should have a couple of pulleys on the Z-axis — one of them ought to be static and held in place by its bolt, so arguably doesn’t need its set screws — you could remove one of those temporarily.


I was having similar problem, my solutions were 1st I had grabbed a dremel up spiral side cutting bit which had way too much flex and 2ndly my z axis was out of calibration so I checked and tightened the belt and calibrated for belt stretch, I believe it’s too new for any stretch but the calibrating was nessasary.(sp?) I had checked the pulley screws, on flats, tightened with thread lock already, which previously had paid it’s dividends thanks to Richard and Will.

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I got a bag of them off amazon for cheap…

A little loctite will keep them from disappearing in the future for the most part.

dead link alert… fyi

another dead link alert…

fixed both.


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Thank you, Will! The set pulley info is what I was looking for last night.

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