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Author Topic: Those pesky circles  (Read 20828 times)

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Offline james elder

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Those pesky circles
« on: August 31, 2006, 12:33:47 PM »
The new forum is much better, the advice is still the same.- excellent

More used to large non critical work, I have been able to live with the error/s shown in the photo, but now I need to sort them. As well as the obvious, I seem to be missing steps, in that after travelling left to right,and back again, for say 100mm, I am 2mm short....and you guys work in thou.. The other axes seem ok.

Where do I start in my search for a cure.. well after reading  previous posts, trying a bunch of stuff, and getting confused, that is...

thanks in advance

Jim
« Last Edit: August 31, 2006, 11:01:06 PM by ynneb »
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Hood

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Re: Those pesky circles
« Reply #1 on: August 31, 2006, 02:24:05 PM »
Are the smaller circles worse than the bigger ones? if so then backlash may be a factor as with the smaller circles you will have the same backlash but with travelling a smaller distance it will show up more I think.
Hood
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Offline james elder

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Re: Those pesky circles
« Reply #2 on: August 31, 2006, 03:20:19 PM »
Thanks for reply Hood.
Yes it does show up more on small things, so..it could be backlash, as you say.
I saw something (i am on Mach 2 by the way) a tickbox for backlash on or off, but when checked I started losing steps badly. I always wondered how you could tell by listening if steps were being lost. I guess it's that momentary low groan before the weeeeeeeee

Is it possible to tell from the shape of the circle where the slackness lies? they seem taller on the left than they should be so...the slackness must be in the drive from left to right not kicking in fast enough, because of some play or looseness.

Am I thinking about this right?

thanks again.. it helps loads to have someone else thinking about it.

Jim
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Hood

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Re: Those pesky circles
« Reply #3 on: August 31, 2006, 03:34:33 PM »
Easiest way to see what backlash you have is to put mag base with  a dial on the table with the stylus on the spindle. Jog one way so the dial reading is near its max travel, zero the glass then go to MDI and do a movement in the opposite direction and see what the difference between the command move and dial is. Repeat for the other axis.
Hood
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Offline james elder

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Re: Those pesky circles
« Reply #4 on: August 31, 2006, 04:02:20 PM »
Will do Hood, thanks.
I did read this or a similar method in previous posts. I guess was hoping for an easier answer, but I'm on it now.

Jim
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Offline Brian Barker

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Re: Those pesky circles
« Reply #5 on: August 31, 2006, 09:48:17 PM »
Could you please tell me what you are running for drives? Also what is your steps per unit...
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ynneb

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Re: Those pesky circles
« Reply #6 on: August 31, 2006, 10:59:08 PM »
Mine are just the same as yours, and like you, it hasnt been so criical. It would be nice to see the answer for this problem. I have always written off the reason I had the problem was too few steps per unit. Not enough gear reduction either.
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Offline ART

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Re: Those pesky circles
« Reply #7 on: August 31, 2006, 11:07:36 PM »
Hi:

 Those are pretty horrible circles. Sorta chewy parabolas glued together..

 First, you need to back up and run some tests.

Zero your machine.

Command G0X10 and measure it. Did it move exactly 10?
Do same for the Y.
Repeat 10 times , is it the same each time.

Now, mark a spot, zero on that spot. Command a file with

G0X10
G0X0
(repeat 10 times)

 Did it come back to zero..exactly...
If not, rezero, repeat 10 more times. Is it off the same distance, or different?

We'll go from there.. :)

Regards,
Art
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Offline james elder

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Re: Those pesky circles
« Reply #8 on: September 01, 2006, 08:08:25 AM »
Thanks for input guys. I'll get back to you asap with answers.

Jim :)
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Offline HillBilly

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Re: Those pesky circles
« Reply #9 on: September 01, 2006, 08:20:07 AM »
This sure looks like backlash in the X axis ( or what I labeled the X axis.). If you look at the 12 and 6 o'clock positions, where the Y axis changes direction, they are almost perfect. Now compare them to the 3 and 9 o'clock positions where the X changes direction.

If this is a servo machine you could be accumulating error pulses in the X drive before movement. Increasing the I gain should help if this is the case.

Darek
« Last Edit: September 01, 2006, 08:22:16 AM by HillBilly »
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