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Author Topic: circles -- oval shape  (Read 9599 times)

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Offline Wayne

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circles -- oval shape
« on: September 18, 2007, 11:06:41 AM »
Hi
I started with Mach 3 a few weeks ago and haven't been able to resolve an issue, so I am looking for some help.

 I have a Gantry Torch cutting setup and am using the plasma profile. When I do a test like X30 Y30 it is very very accurate.  When I do a 4 in. circle my Y axis is +0.187 in. and X axis is -.0625 creating a very symetrical oval. All motor movements are very smooth.

Here is what I have tried so far;  Exact stop mode enabled
                                              Eliminate any compensation modes
                                              absolute and incremental modes
                                              G12 mode
                                              changed ramping rates, this did help, X axis has 2/1 ratio, Y axis is 1/1
                                              Backlash on both axis is less than .015
                                              Switched Gecko drives, no difference
                                              installed new shielded cable thru the entire system
                                              1.8 Ghz computer with 1gig ram (ouch!)
 

I have tried everything I can come up with, maybe someone can spot a simple fix I have overlooked. Any help is much appreciated !

Very Frustrated
Wayne

Offline Chaoticone

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Re: circles -- oval shape
« Reply #1 on: September 18, 2007, 11:33:58 AM »
Hey Wayne, can you post your code?

Brett
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Offline docltf

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Re: circles -- oval shape
« Reply #2 on: September 18, 2007, 11:46:04 AM »
me too
     
       i have a little test g-code that cuts a 1.0 inch circle and a 1.0 inch square in the same run.it cuts them so i can
       mic them from the outside.the circle cuts oval and the square x =1.006   y=1.009     
       i also have checked my machine all over.last friday i started going back to previos versions looking for the change
       have not found anything yet.

bill

Offline Wayne

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Re: circles -- oval shape
« Reply #3 on: September 18, 2007, 11:48:06 AM »
Here are 2 examples and setup files.

Offline Wayne

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Re: circles -- oval shape
« Reply #4 on: September 18, 2007, 11:54:39 AM »
Sorry didn't get them all in that post. I'll try again ;)
Re: circles -- oval shape
« Reply #5 on: September 19, 2007, 08:31:54 AM »
Have you checked your steps per unit? also do you have much for backlash?
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Offline Wayne

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Re: circles -- oval shape
« Reply #6 on: September 19, 2007, 02:59:04 PM »
Hi
Yes, steps per inch are correct and when I do a straight line test the measurements are right on.  When I make a square or a circle ( something enclosed) my Y axis is long and my X axis is short, usually Y is about
 2 % long and X is about 1 % short.  Backlash is .010 to .014.  I did try programing in for backlash, it did not help.  The error amount is proportional to the dimension of the item.  aka. 2" circle off .125   4" circle off .250.  I was thinking maybe noise or the Gecko drivers were off, so I switched x & y drivers, it had no affect.  Then I replaced all cables with better shielded ones and put each driver in a separate metal encloser to reduce the chance of noise or false triggering,   it did not help either.   I am using a Campbell Iso board  and a new Printer Port cable.  The Iso Board is also in its own metal encloser.  I've tried everything I can think of and am totally stumped !

Thanks
Wayne

Offline Graham Waterworth

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Re: circles -- oval shape
« Reply #7 on: September 19, 2007, 05:19:24 PM »
When you say the straight line measurements are spot on, how spot on, what are you using to check the distance, and over what length.

If the error is proportional then the steps per inch/mm must be wrong.  Are your backlash figures inches or metric?

when you check the distance moved have you removed the backlash first?

Graham.
 
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Offline Wayne

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Re: circles -- oval shape
« Reply #8 on: September 19, 2007, 07:26:16 PM »
My straight line measurements were 48 inches long, both x and y axis, measured with a 12 inch digital caliper and manually held by hand to take up backlash.  I am using ground and polished acme threaded rod for travel. My measurements are all in inches.  My x axis motor has a 2/1 reduction. !.8 degree stepper  and 5tpi acme threaded rod and 10 microstep gecko drive -----20,000 spi.  My y axis is 1/1 ratio with 10 microstep drive, 1.8 degree and same 5 tpi threaded rod-----10,000 spi.  Testing is done at normal cutting speeds  8 ipm to 17 ipm.

Thanks
Wayne
Re: circles -- oval shape
« Reply #9 on: September 19, 2007, 10:12:03 PM »
if it is noise try this as a file
G00 X0.0
G4 P1
G00 X6.0 Y0.0
G12 I3 F100000
M47

Let this run for 20 min and check to see how far off it is from where it started with a dial indicator. I would set the inicator at X 0.0 and check it during the 1sec dwell that you have in the file.

thanks
Brian
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