# Polycarbonate Engraving Issues



## mgreen7745 (Mar 18, 2021)

I a high school student who is new to CNC routing/engraving and was making a plaque for someone at my school when this happened. This was a 1/4" 4 flute carbide chamfer tool in 1/4" polycarb on an EZRouter and the toolpath went from bottom to top and was only supposed to go 1/8" into the stock. It looks like the z height decreased as the toolpath continued and eventually broke through. My first thought was too high of a plunge rate that caused me to lost steps, but I don't think that is the culprit. Any suggestions on what this could be or ways to improve would be appreciated.


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## difalkner (Jan 3, 2012)

Welcome to the forum! What software are you running - design (CAD/CAM) and CNC controller? Four flutes may be too many for plastics, fwiw. Can you rerun the program in the air, say 1" above the workpiece, and see if it dives in with nothing cutting?

David


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## mgreen7745 (Mar 18, 2021)

difalkner said:


> Welcome to the forum! What software are you running - design (CAD/CAM) and CNC controller? Four flutes may be too many for plastics, fwiw. Can you rerun the program in the air, say 1" above the workpiece, and see if it dives in with nothing cutting?
> 
> David


I can try rerunning it, I know that this router has had z axis issues before and I may have just gotten unlucky. I used VCarve.


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## mgreen7745 (Mar 18, 2021)

mgreen7745 said:


> I can try rerunning it, I know that this router has had z axis issues before and I may have just gotten unlucky. I used VCarve.


No CAD only text in VCarve and the router is controlled by Mach3 I believe.


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## difalkner (Jan 3, 2012)

If it has had Z issues before then I would check everything mechanical and electrical - all connections, couplings, set screws, etc.

David


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## mgreen7745 (Mar 18, 2021)

difalkner said:


> If it has had Z issues before then I would check everything mechanical and electrical - all connections, couplings, set screws, etc.
> 
> David


You are probably right, I just wanted to see if there was something obvious that I was missing.


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## old55 (Aug 11, 2013)

Welcome to the forum.


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## gwilki (Nov 12, 2012)

David's suggestion to run the job in air to see if the Z drops is a good starting point. I wonder if, with all the melting, the drag on the bit threw your Z position off. Feeds and speeds in acrylic can be frustrating. If you have access to an o-flute or a single flute bit, you may be better off using it.


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## markbdusted (Dec 26, 2013)

mgreen7745 said:


> I a high school student who is new to CNC routing/engraving and was making a plaque for someone at my school when this happened. This was a 1/4" 4 flute carbide chamfer tool in 1/4" polycarb on an EZRouter and the toolpath went from bottom to top and was only supposed to go 1/8" into the stock. It looks like the z height decreased as the toolpath continued and eventually broke through. My first thought was too high of a plunge rate that caused me to lost steps, but I don't think that is the culprit. Any suggestions on what this could be or ways to improve would be appreciated.
> View attachment 398107
> View attachment 398108


I suspect the bit was not tightened securely and pulled down from the collet.
The 4 flute bit likely was galling and the extra load just overcame the collet's ability to hold the bit.


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## wyzarddoc (Dec 31, 2006)

mgreen7745 said:


> I a high school student who is new to CNC routing/engraving and was making a plaque for someone at my school when this happened. This was a 1/4" 4 flute carbide chamfer tool in 1/4" polycarb on an EZRouter and the toolpath went from bottom to top and was only supposed to go 1/8" into the stock. It looks like the z height decreased as the toolpath continued and eventually broke through. My first thought was too high of a plunge rate that caused me to lost steps, but I don't think that is the culprit. Any suggestions on what this could be or ways to improve would be appreciated.
> View attachment 398107
> View attachment 398108


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## wyzarddoc (Dec 31, 2006)

Several things to check. 1.Use only 1 or 2 flute mills when cutting plastics. 4 flute mills are for large metal milling machines running at way lower RPM's 2. Be very sure your hold downs are not moving in a vertical Z direction along with the X and Y directions. 3. Be sure your not bottoming out the bit when you put it in the router. If you bottom out the bit it can spin and drop down with the heat and torque generated when cutting plastic. Also use the slowest router speed you can and adjust the feed rate also
Just my $0.02 learned the hard way


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