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Author Topic: CNC or Mach3 calibration issue?  (Read 3591 times)

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CNC or Mach3 calibration issue?
« on: October 17, 2009, 04:42:16 PM »
Hi All,

Having an issue with my cnc where as i'm unable to calibrate it correctly.

I've been using the auto calibration feature and following the below steps:

Set up a digital sliding scale on the x axis
Auto calibrate 1000mm actual move 1001.89 save changes
Test again runninga code in the MDI: G001 X1000, actual measurement 999.99...
But then i test in 100mm increments and i get the following:

1 = 1.01
100 = 99.50
200 = 199.72
300 = 299.63
400 = 399.66
500 = 499.72
600 = 599.81
700 = 699.92
800 = 800
900 = 899.98
1000 = 1000.04
 
???

My cnc is a toothed belt gear set up (no thread on x and y only on z).

What i'm trying to figure out is whether its something mechanical with the cnc or is there a setting or set up i'm missing with Mach3?

If any one has any ideas or thought it would be great to hear as i'm really stuck on this and can't start using the cnc until i get it sorted
Many thanks in advance
Glenn

Offline RICH

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Re: CNC or Mach3 calibration issue?
« Reply #1 on: October 17, 2009, 05:24:08 PM »
Glenn,
Could be there is variation in the belt and even the pulleys. If you reverse the direction you sould get the same differences.
RICH
BTW: That's a long distance, due you also know for gact that the digital scale is accurate.
 
« Last Edit: October 17, 2009, 05:26:35 PM by RICH »
Re: CNC or Mach3 calibration issue?
« Reply #2 on: October 17, 2009, 07:39:37 PM »
Hi Rich,

Yes that was something i was thinking that it could be in the pulleys...i did following test:

X + 500 =499.65 (i then zero'd the scale)
X - 500 = -499.63
X + 500 = 499.57
X - 500 = -499.61
X + 500 = 499.65
X - 500 = 499.62
X - 500 = 499.54

I also tried adding backlash (although i'm not very familiar with this setting)

same as above moving forward 500, zero the scale, then back 500

backlash .05 @ 20% speed

499.84
-499.63
499.58
-499.59
499.59
-499.61

Not sure if the above makes sense or if that indicates a backlash issue as the figures are still inconsistent?
Cheers
Glenn

Offline RICH

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Re: CNC or Mach3 calibration issue?
« Reply #3 on: October 17, 2009, 09:04:46 PM »
Glenn,
 Move your X, say x + 10, now zero your Dro's and also your scale.
Now using MDI do a X +500
Then do a X-500

You should be back to X=0Zero, and if not then you have some backlash, even if your steps are not correct.
If your steps per unit are correct then the difference is your backlash and that is the number you should use for setting the backlash amount in CONFIG>Backlash.
Save those setttings and then try the same thing above and you should return to zero.
Note that you used the same run of belt when you did that.
Now step from X=zero in 100 movements, in one direction, to 500, and see if they are all equal on your ref scale. If not then then there is error in the belt / pulleys.
RICH
MODIFIED: if you are in the absolute mode then you would do a ..... G0 or  G01 to X 0.0
« Last Edit: October 17, 2009, 09:57:35 PM by RICH »