Cut Path Question

Screenshot 2023-12-11 at 5.10.04 PM
Screenshot 2023-12-11 at 5.09.55 PM

I’m baffled about what went wrong here and any insight would be appreciated. So I posted the toolpaths of three acrylic bases for a product and the simulations. The last photo shows a 4th object that is not in the file. And it’s cut all erratically. What could have caused this?


Avoid slotting.

Consider leaving a roughing clearance and taking a finishing pass.

No - that last cut WAS NOT in the file. If you look…there are only three to be cut and it started a 4th.

Can you post a wide shot of your whole machine?

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This is what happens when the machine loses steps - the controller program is fine, but the machine started losing steps somewhere along the way until it caused a major offset. Where the spindle was actually positioned no longer matched where it was supposed to be according to the controller. If you checked your machine XYZ Zero point after the cut, you’d find it’s way off from when you started the cut.
Looks like it lost mostly in the Y-axis & the Z-axis since it cut through the top of the acrylic during a rapid move but the X-axis position looks nearly straight. Also, by the uneveness of the cutting, your tool was either getting gummed up & causing random/changing resistance forces or your machine is mechanically loose in some way…or both.

As Will Adams mentioned, cutting slots can be hazardous as chips have no where to go but up and the tool can create extra heat rubbing almost constantly against the sides of the slot. With acrylic, this can easily result in melting which can then stall the motion of the tool through the material resulting in loss of machine Zero point.


That cut was in the file - it’s just that the machine ended up in the wrong place, and so that cut was mis-placed. The reason the machine ended up in the wrong place is that it commanded move that didn’t complete properly, so the machine “lost steps”.

Why wouldn’t a move complete properly? It could be a mechanical / electrical problem (for example, a bad electrical connection to a motor), OR it could be the machine was unable to move as fast through the material as the code said it should (it “bogged down”).

As @WillAdams says, you want to avoid slotting (a cut the width of the tool), and you should carefully check for any mechanical problems (debris on the rails, dust collection hitting something, lack of lubrication, etc), AND check for electrical problems - do any of the connector get hot dureing use, or are the discolored from heat, or is there corrosion on any of the pins.


Thank you so much! This was my first attempt at acrylic. I knew it was a “thing” to do acrylic, but I got the suggested bit, researched the feeds and speeds, etc.

Your explanation makes perfect sense. I don’t do a lot of this work (thankfully), but this is something that makes sense to me.

Thank you so much for your thoughtful and well explained answer!!!

Thank you so much for this! I’ve never done anything other than wood, so this is a new medium for me.

I appreciate the time you took to respond and explain it to me!!!

You may be cutting too aggressively with respect to RPM. If you selected tools for soft plastic, try selecting hard plastic and remake the toolpath. I wasted alot of acrylic when starting. Too many rpms and the bit would heat up and melt the plastic, plastic would flex and grab the bit pulling an upcut bit down into the wasteboard, losing steps in Z. etc. Trial and error is your friend here.

Be sure nothing is restricting gantry movement (vaccuum hose?, clamps?)

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