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Author Topic: Kernal Speed and Chatter  (Read 8773 times)

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Kernal Speed and Chatter
« on: September 12, 2009, 08:03:56 PM »
I am having a problem with chatter on my cuts.  There are members of another forum were I built my machine that think the chatter is caused by the kernal not being set at a high enough rate or that the Dell Pentium III machine is having a problem processing the files.  I ran the test program that comes with Mach and the computer passed the test.  Is there anther way to check for kernal speed or a computer problem with regards to the kernal.

I am starting to question that it might be the computer.  I am cutting a diamond shape that has 2" length legs with the diamond sitting on a point so the cuts are at a diagonal.  I am cutting solid surface material with .5" O Flute End Mill.  When I cut this small pattern, there is considerable chatter.  Tonight I cut a small 45 degree 4" cut and there was chatter marks but the cut was smooth.  

The last cut makes me wonder if I am having a computer problem and the bad chatter I am getting is the result of the computer not being able to process the cut commands and is skipping.

I would appreciate some input or suggestions.

Thanks
« Last Edit: September 12, 2009, 08:05:45 PM by SailFl »

Offline Hood

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Re: Kernal Speed and Chatter
« Reply #1 on: September 12, 2009, 08:08:27 PM »
more likely to be mechanical issues, if you do a straight cut along an axis do you see problems?
Hood
Re: Kernal Speed and Chatter
« Reply #2 on: September 12, 2009, 08:22:16 PM »
Hood,

After the two test I just described, I don't think it is mechanical.  The diamond cuts are at a 45 degree angle and the chatter is bad at a slow 35 IPM.  The 4" 45 degree had chatter marks but the cut was smooth.

So I don't think it is chatter.  Straight cut are okay.

I have been over my machine and it is tight.

Offline Hood

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Re: Kernal Speed and Chatter
« Reply #3 on: September 12, 2009, 08:27:40 PM »
What kernel do you have it set at and what are your velocities and steps per unit?
Hood

Offline ger21

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Re: Kernal Speed and Chatter
« Reply #4 on: September 12, 2009, 11:51:57 PM »
What kind of drives are you using? Can you post a video? does the machine sound rough?

Also, why are you cutting so slow. With a sharp spiral bit, you can easily cut solid surface at 300ipm.
Gerry

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Re: Kernal Speed and Chatter
« Reply #5 on: September 13, 2009, 12:58:22 AM »
My Opinion... this is a CV Issue.  I have been noticing the same issues with a large Foam Band saw I recently built.  I have tried playing around with the CV settings but optimize this but IMHO, due to the fact that the machine is large and has a lot of mass (therfore really slow accels) there is a large speed differential between my X & Y axis (X is belt driven & Y is lead screws) there is simply not enough ability to equalize the CV in order to compensate for one axis being so much slower.

I wish some one had an answer to this.  Just my $.02

Sid
Re: Kernal Speed and Chatter
« Reply #6 on: September 13, 2009, 11:59:58 AM »
Sid,

I think you are on to some thing with the CV issue.  I lookd over the document on CV and I wish the author would have included some number examples for settings.  Also it would be nice to know what the values mean.

The default for Distance Tolerance is 180 and I set my to 100.  I also set my Stop CV Angle to 90.  My look ahead to 200.

I recut my test Diagonal cuts at 35 and 70 IPM and things were smooth but when I cut at 100 IPM my chatter was back.

So I think that these parameters are making an impact. 

If any one has some experiencing with these setting please post your settings or what your experience has been.

Ger21:  I am cutting at these speeds because I am getting chatter.  I would love to be able to cut at 300 IPM with no chatter.  But chatter doesn't go away when you cut faster, it only cuts faster.  At least that is what I am experiencing.

I will be happy to report my experience and settings when I have done some more testing.

Thanks for the suggestion.
« Last Edit: September 13, 2009, 12:02:14 PM by SailFl »
Re: Kernal Speed and Chatter
« Reply #7 on: September 13, 2009, 12:05:36 PM »
Just for 'Grins'- perhaps you can try to cut in Exact Stop mode and see if you are able to reach your 300 IPM target and NOT get the chatter?  This eliminates the chatter for me but changes my cut in an undesireable way so I am kinda locked into using CV.

vmax549

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Re: Kernal Speed and Chatter
« Reply #8 on: September 13, 2009, 03:17:13 PM »
If you have cutter chatter I don't think you will find it is a software problem. Chatter is generated from a component NOT rigid enough to hold it in place. It flexes then jumps back into place and flexes ,etc,etc.

Could be DOC too large for the machine or material or too fast feedrate for the cut. OR spindle speed too slow for cutter specs and feedrate.

I have never seen software CAUSE tool chatter in itself. I always had to help it occur (;-)



Just some thoughts, (;-) TP
Re: Kernal Speed and Chatter
« Reply #9 on: September 13, 2009, 03:30:50 PM »
VMAX-

Respectfully, I have to disagree.

If you have a machine with a lot of mass and the accel rate is set too high then a rapid acel will cause your machine to jerk, then this will result in what I am interpreting as chatter.  Perhaps I am mistaken or using the incorrect terminology.  If so, I apologize in advance.

While what you say is partially true because the "chatter" it is due to the mass limitations of the machine, the software allows us to slow down our accels to a point where things become smooth.

CV takes this away from us to a certain extent because Mach now want to control velocity on it's own terms (well sort of) but we certainally do not have the same speed/accel control as in exact stop mode.  If 2 or more of your axis are dissimilar in terms of their tuning profile, you will see Mach slowing down one axis a lot more rapidily than the other in an attempt to keep things "Constant"  this struggle can result is Jerky motion (exactly what CV is supposed to prevent).  CV is a double edged sword under these circumstances.

Sid