Why you should not run unattended

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twforeman
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Why you should not run unattended

Post by twforeman » Tue Mar 08, 2016 2:48 am

You should never run your Shapeoko 1, 2 or 3 (or any other variant, or any other CNC machine for that matter) unattended.

This is one example of why.

Image

I was milling 0.830" diameter 1.100" deep holes in MDF with a 1/4" two flute carbide router bit. The cutter was a little dull at the start, and not really the one I should have been using.

I was helical milling the holes in two passes.

The first pass was 0.450" with a 0.100" ramp down per revolution. I ran it at 39 IPM and it seemed to go okay.

The second pass was much more aggressive (because GWizard and the CNC Cookbook blog said it should work - with an end mill, not a router bit...) I helical milled to 0.830" diameter with a 0.300" inch ramp down per revolution at 32 IPM.

You can tell by the first hole that I was in trouble. It's oval shaped.

I was in the shop but not really watching the machine too closely. I heard it when it got into real trouble and ran over and hit the reset button (no E-Stop wired up yet - though it was almost on fire.)

Let's break it down a little:
  • Wrong cutter
  • Dull cutter
  • Straight flutes on the cutter did not expel the dust well enough
  • Overly-aggressive cut
  • First run of a new tool path
  • MDF
The oval shape suggests to me that the dual Y motors were able to push the dull bit hard enough but the single X motor was not. Then it started losing steps and got totally into the weeds.

If I had not been in the shop it probably would have caught on fire after a bit as it tried to drive the end mill sideways at 1.100" deep through solid MDF. You can see where it started burning.

As a side note: MDF is terrible stuff to mill. It dulls the cutters almost right away. I've been doing some reading and 2 flute end mills with TiAN coating are suggested. I have one coming to try out.
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AnonymousPerson
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Re: Why you should not run unattended

Post by AnonymousPerson » Tue Mar 08, 2016 3:33 am

Reinforces needing a fire extinguisher (dry type) near our machines eh? :)
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tek
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Re: Why you should not run unattended

Post by tek » Tue Mar 08, 2016 3:56 am

That's why one needs e-stop, I plan to install one ASAP too. The GWizard is not good for wood. I used it for recommendations for feeds and speeds and its way too aggressive for hardwoods. Even at hardwood setting the feeds and speeds it delivers only work for soft woods, for anything harder its way too aggressive. Something to keep in mind if you work with wood.

chamnit
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Re: Why you should not run unattended

Post by chamnit » Tue Mar 08, 2016 5:25 am

Just curious. Do you recall what GWizard computed the (lateral) cutter forces as?

Brian Stone
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Re: Why you should not run unattended

Post by Brian Stone » Tue Mar 08, 2016 7:13 am

AnonymousPerson wrote:Reinforces needing a fire extinguisher (dry type) near our machines eh? :)
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AnonymousPerson
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Re: Why you should not run unattended

Post by AnonymousPerson » Tue Mar 08, 2016 8:49 am

Brian Stone wrote:One of my first investments.
Same here. :)
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Jimf
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Re: Why you should not run unattended

Post by Jimf » Tue Mar 08, 2016 12:49 pm

I try not to leave machines unattended but sometimes you need to get another cup of coffee or bathroom break. I put a remote wifi camera in my shop that I can view on my phone.

The room is also equipped with several fire extinguishers and smoke alarms. Now that I have a laser cutter, it is very important to keep a eye on things.

AnonymousPerson
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Re: Why you should not run unattended

Post by AnonymousPerson » Tue Mar 08, 2016 1:01 pm

Wonder how hard it would be to create a remote kill switch, such that if something nasty shows up in the remote camera it's possible to turn everything off (emergency stop style).

Thinking it through... shouldn't be too hard. Would probably be useful too. Hmmm, might have a play around with things later. :)
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Jimf
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Re: Why you should not run unattended

Post by Jimf » Tue Mar 08, 2016 1:16 pm

AnonymousPerson wrote:Wonder how hard it would be to create a remote kill switch, such that if something nasty shows up in the remote camera it's possible to turn everything off (emergency stop style).

Thinking it through... shouldn't be too hard. Would probably be useful too. Hmmm, might have a play around with things later. :)
I saw a wifi enabled power strip that someone used for a 3D printer. Those printers can be a fire hazard if the hot print head goes thermal runaway. Not sure where you can find the power strip.

WillAdams
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Re: Why you should not run unattended

Post by WillAdams » Tue Mar 08, 2016 1:26 pm

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