Hello Guest it is July 21, 2019, 05:39:21 AM

Author Topic: Drifting in the Y axis  (Read 4373 times)

0 Members and 1 Guest are viewing this topic.

Drifting in the Y axis
« on: December 17, 2009, 05:18:20 AM »
I've had a Sieg KX3 CNC mill for about a year now and it's always had an issue with 'drifting' + in the Y axis. If I zero Y to the edge of the vice then run a program to say cut a pocket in several levels in Z I can see by the faces of the pocket that it drifts (steps on one side, smooth on the other). If I then go back to find the Y edge of the vice again I find that Y has drifted about +0.5mm. This figure will depend upon the length of program run, longer program, bigger drift. Any ideas?

Kind regards
Rob

Offline Tweakie.CNC

*
  • *
  •  7,850 7,850
  • Super Kitty
    • View Profile
    • Tweakie.CNC
Re: Drifting in the Y axis
« Reply #1 on: December 17, 2009, 06:50:32 AM »
Just a thought but if you are using stepper motors then it could be that you are loosing steps. One of the most common causes of this is binding or tight spots on the axis travel coupled with insufficient drive torque from the stepper motor.
As it is only occurring on the this one axis and only in one direction I suggest you look for a mechanical cause before suspecting anything else.

Tweakie.
Success consists of going from failure to failure without loss of enthusiasm.  Winston Churchill.
Re: Drifting in the Y axis
« Reply #2 on: December 17, 2009, 08:52:39 AM »
Thanks Tweakie, I'm trying all avenues at the moment. I've already tried cleaning and adjusting the gibs and tried winding the ball screw by hand and it all appears fine in both direction +&- Y. I assume it is mechanical rather than software but it's worth asking the question just in case.

Rob

Offline RICH

*
  • *
  •  7,342 7,342
    • View Profile
Re: Drifting in the Y axis
« Reply #3 on: December 17, 2009, 01:55:09 PM »
Sounds like a loose ball nut or backlash.
RICH
Re: Drifting in the Y axis
« Reply #4 on: December 17, 2009, 02:02:09 PM »
Might also check all keys, pulley set-screws and couplings for any slippage.
Depending on the rapids and heavy feeds, it's possible to only loose or gain in 1 direction.
RC
Re: Drifting in the Y axis
« Reply #5 on: December 17, 2009, 07:00:44 PM »
Sounds like a loose ball nut or backlash.
RICH
If it gets worse with longer programs, backlash wouldn't explain a slow drift over time that gets worse.  Although the getting worse after running fine might suggest wear or loose parts, a series of increasing gaining or losing steps can be computer related as well. 
Is the PC dedicated only to Mach use?  Have you recently changed versions?  If the machine is used for other things, cumulative system changes or resource allocations for other programs can take time from the system or mess up your pulse stream.
Likewise are you running higher feeds now than you were before?  Loading the machine harder?  Lots of things to check through. 

Offline alenz

*
  •  137 137
    • View Profile
Re: Drifting in the Y axis
« Reply #6 on: December 17, 2009, 10:19:06 PM »
I seem to recall a similar instance being reported which was a result of the step/dir being set to high when it needed to be set low, (or vice versa). A step would sometimes be lost when the direction reversed. I think the fix was to check (or uncheck) the low enable in Config > Ports & Pins > Motor Outputs and then go to Config > Homing/Limits and check/uncheck the Reversed block to get the proper direction back.  Probably a long shot and I’m just going on memory :)
Al
Re: Drifting in the Y axis
« Reply #7 on: December 18, 2009, 03:19:34 AM »
Thanks everyone for your input. Just to answer a few questions, the PC is a dedicated and high powered machine. It has just the OS (XP) and Mach3 on it and is not connected to any other device.
I did some testing a while ago and if I zero Y to something solid then move + & - in Y a few times and check Y again I can see it has drifted + in Y. Thing is it's fairly repeatable and only appears to loose steps in the -Y direction but not the +Y. I've cranked the Y axis by hand and it feels fine. I've checked the backlash and it's 0.02mm, which is fine. I'll check the couplings and any other fixings I can find. Thanks again.

Rob

Offline Hood

*
  •  25,849 25,849
  • Carnoustie, Scotland
    • View Profile
Re: Drifting in the Y axis
« Reply #8 on: December 18, 2009, 03:31:29 AM »
What make of drives do you have? What do you have for Pulse Width and Dir Prechange? Do you have the same settings for Active High/Low as with the other axis?
Hood

Offline Tweakie.CNC

*
  • *
  •  7,850 7,850
  • Super Kitty
    • View Profile
    • Tweakie.CNC
Re: Drifting in the Y axis
« Reply #9 on: December 18, 2009, 03:44:09 AM »
Rob, would it be possible to increase the drive current (just slightly) to your Y axis stepper (do you have adjustment on your driver card for this) ?.

Tweakie.
Success consists of going from failure to failure without loss of enthusiasm.  Winston Churchill.