3D Profile of Reddit Alien

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levlandau2
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3D Profile of Reddit Alien

Post by levlandau2 » Sat Mar 02, 2013 4:42 pm

So I have wanted to explore the potential for more sophisticated 3D profiling for some time. The pink foam at home depot (Foamular) seemed like a good material to use for such tests. It is uniform and does not have the voids which the white foams do and comes in 2" thickness allowing for some large objects to be milled. Also the foam is soft so it is ok to mill at 1mm passes and 2000 mm/min feed rates.

I used this Reddit Alien model I found on thingiverse and Cambam to generate the gcode. First I did a roughing pass and then a vertical 3D profiling pass. Overall the results are decent and I think the ShapeOko can mill nice 3D objects.

The one big problem I encountered is the length of time it took to complete the 3D profiling pass. It seems to generate the complex oval curves on this object, Cambam broke the curves into many segments. So during each segment the spindle had to accelerate and decelerate, not necessarily reaching maximum velocity due to the short length of the segments. This sequence of event really slowed things down, even though I had set the feed rate to ~2000 mm/sec. This issue needs to be corrected to make the time it takes to mill such a profile bearable.

In summary, does anyone know how to avoid the acceleration and deceleration when milling 3D profiles? This would greatly speed up such operations.
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WillAdams
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Re: 3D Profile of Reddit Alien

Post by WillAdams » Sat Mar 02, 2013 5:58 pm

levlandau2 wrote:In summary, does anyone know how to avoid the acceleration and deceleration when milling 3D profiles? This would greatly speed up such operations.
1 - use a tool which elegantly (in the sense of scientifically minimally correct) generates arcs instead of polylines
2 - use/enable the option which downloads multiple commands alowing GRBL to ``look ahead''
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Will Winder
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Re: 3D Profile of Reddit Alien

Post by Will Winder » Sat Mar 02, 2013 9:41 pm

WillAdams wrote:
levlandau2 wrote:In summary, does anyone know how to avoid the acceleration and deceleration when milling 3D profiles? This would greatly speed up such operations.
1 - use a tool which elegantly (in the sense of scientifically minimally correct) generates arcs instead of polylines
2 - use/enable the option which downloads multiple commands alowing GRBL to ``look ahead''
For #2, I thought GRBL did that by default. Is that not the case?
levlandau2 wrote:In summary, does anyone know how to avoid the acceleration and deceleration when milling 3D profiles? This would greatly speed up such operations.
What tool are you using to send the gcode? Maybe its only sending them one at a time instead of 128 bytes at a time.
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WillAdams
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Re: 3D Profile of Reddit Alien

Post by WillAdams » Sat Mar 02, 2013 9:50 pm

In Grbl Controller 3.3.3 under Tools | Options there's a checkbox for:

Use aggressive preload strategy for Grbl

which is off by default --- are there any senders which default to on?
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cvoinescu
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Re: 3D Profile of Reddit Alien

Post by cvoinescu » Sat Mar 02, 2013 10:50 pm

I may be wrong, but I think GRBL Controller is the only one that has the option to turn that feature off. There's no point in it ever being off, except maybe for debugging. Even with "aggressive preload" on, though, GRBL has a limited look-ahead buffer, so it may not get to full velocity if the segments are really small. Arcs don't help much, because GRBL breaks them into segments internally and those go into the planner. Again, I may be remembering incorrectly, but I think Marlin has a larger look-ahead buffer. Of course, it needs an Arduino Mega; and it defaults to different pins, but that's configurable -- but not plug-and-play. FWIW, TinyG and LinuxCNC will both do an even better job.
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levlandau2
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Re: 3D Profile of Reddit Alien

Post by levlandau2 » Sun Mar 03, 2013 12:50 am

I used LinuxCNC to mill this. The gcode file is 35k lines, so quite a lot of segments.

So do I have incorrect settings in LinuxCNC for the lookahead? This doesn't seem like a practical way to mill arcs in a 3D profile.

Will, what tool would you recommend that makes arcs instead of segments? I have had the best experience with Cambam so far.

WillAdams
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Re: 3D Profile of Reddit Alien

Post by WillAdams » Sun Mar 03, 2013 3:19 am

Still learning myself, and I've been hand-coding G-code, so am somewhat dis-heartened by Cat's statement.
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cvoinescu
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Re: 3D Profile of Reddit Alien

Post by cvoinescu » Sun Mar 03, 2013 11:13 am

I don't know how to configure LinuxCNC. I don't have a machine at the moment (long story), or I'd try your code with GRBL and Marlin. Sorry if I said things that aren't true -- they're based on what I remember reading all over the place, so they may be woefully out of date, for instance.
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WillAdams
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Re: 3D Profile of Reddit Alien

Post by WillAdams » Sun Mar 03, 2013 12:30 pm

I think there was some discussion of this sort of thing before. Perhaps different settings will help? I seem to recall a ``waterline'' option being faster?
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Improbable Construct
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Re: 3D Profile of Reddit Alien

Post by Improbable Construct » Sun Mar 03, 2013 4:11 pm

I am wondering if why you are seeing is Cambam trying to compensate for different feed and plunge rates.
With my cam software, for example, it disregards plunge rate when doing a 3d model, but it uses the plunge rate as the feed speed when doing ramp cuts.
Try setting your feed and plunge rates to say 1000mm and see what happens.
I may be way off base here. If that dosent work could you post a video showing your mill running and some of the g code running?
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