Machsupport Forum

Mach Discussion => General Mach Discussion => Topic started by: chuckmerja on December 01, 2012, 07:41:30 PM

Title: MACH3 move error
Post by: chuckmerja on December 01, 2012, 07:41:30 PM
We have a Grizzly mini mill with 276 ozin steppers, Gecko 540 (24v) supply, and MACH3. We are making egg shaped circles and want them to be round. 

We have calibrated the axis's and they are both right on (and very similar steps per inch numbers of 15984.********* and 16000.*********x.  And we have redone the backlash, (home made plastic nuts on ACME threads) X was 0.001 and Y was 0.009. And we have restarted MACH several times to and confirmed that the settings have changed.

HOWEVER, when we go to MDI in MACH and tell the X axis to move 0.5", it actually moves 0.455" - and is pretty repeatable (+/- a thou or sometimes 2).

Interestingly (and frustratingly) when we do an 8 hole bolt pattern, and measure the major and minor axis's and subtract the smaller from the larger, we get a difference of 0.046"... note that 0.5-0.455 = 0.046.  We must have some setting messed up, but just can't find it.

Any help would be great!
Title: Re: MACH3 move error
Post by: Hood on December 02, 2012, 04:56:07 AM
Calculate your steps per unit from the screws/drives/reduction etc and see what your numbers work out at, using the inbuilt calibration in Mach is only as accurate as your measuring, calculating the values is as accurate as your hardware.
Also turn off backlash and see how things go, having backlash set incorrectly just adds to the confusion so get things right without it first then, if you must, enable it after things are sorted and you can then get a better idea of the values required for it.
Remember however, backlash is not perfect, its adjusting for the lash you have but it can not correct for tool force on the axis.