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Author Topic: Rippled finish only when cutting arcs  (Read 1848 times)

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Rippled finish only when cutting arcs
« on: December 22, 2015, 02:16:45 PM »
Hello, after many months of mechanical problems with my new lathe I'm now facing a software related problem...

Long story short: lathe had both Z and X axis compromised, ball nuts where pushing the saddle up and down, left and right, so the finish was MECHANICALLY wavy.
Leadscrews have been fixed, sliding surfaces grinded and so on.
When I now cut a straight line (be is only on Z, only on X or any angle) the surface is silk smooth.
So any G1 movement is perfect.

When I make any arc (G02 or G03) I get a rippled finish.
Like here:

I tried J/K, absolute or relative parameters with no luck.

I use servo motors, if this can make any difference.

Controller is a Ethernet kind.

Does Constant Velocity or Exact Stop have any influence with that?

Thanks a lot!


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Offline ger21

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Re: Rippled finish only when cutting arcs
« Reply #1 on: December 22, 2015, 02:25:46 PM »
Possibly a servo tuning issue.
I've seen similar marks on a servo powered router that were due to servo tuning.
Gerry

2010 Screenset
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JointCAM Dovetail and Box Joint software
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Re: Rippled finish only when cutting arcs
« Reply #2 on: December 22, 2015, 02:31:09 PM »
Thanks, how / where do you tune the servo?
Re: Rippled finish only when cutting arcs
« Reply #3 on: December 22, 2015, 04:13:31 PM »
In larger servo drives this is typically caused by the gain being too high or the encoder not having (enough) feedback dampening.
Rippled finish only when cutting arcs
« Reply #4 on: December 22, 2015, 04:22:12 PM »
Thanks a lot, I'll try some different parameters!


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Re: Rippled finish only when cutting arcs
« Reply #5 on: December 22, 2015, 07:06:36 PM »
Is the code actually actually arcs or is it a lot of short lines that make up an arc?
Rippled finish only when cutting arcs
« Reply #6 on: December 23, 2015, 01:29:48 AM »
It's arcs, not lines.
I changed the acceleration parameters and the finish is much better, almost perfect. It looks like it will need some further tweaking but it's a software thing.
Thanks!


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Rippled finish only when cutting arcs
« Reply #7 on: December 23, 2015, 02:44:49 AM »
Here's a photo




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Offline BR549

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Re: Rippled finish only when cutting arcs
« Reply #8 on: December 23, 2015, 10:25:32 AM »
IF you were able to tune it out using the Accel parameters in Mach3 then you definately have a servo tuning problem that you need to sort out.  With a properly tuned servo it would NOT matter what settings you used in Mach3 it would still cut arcs smoothly.

Just a thought, (;-) TP
Rippled finish only when cutting arcs
« Reply #9 on: December 23, 2015, 10:31:35 AM »
Yeah, I suspected that. The lathe is now traveling towards my place, should be here before the 31st. Then I'll have the opportunity to play a bit the servo parameters.
Thanks!


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