Hello Guest it is December 09, 2019, 12:31:42 AM

Author Topic: Position Errors Only on Diagonal Moves  (Read 10387 times)

0 Members and 1 Guest are viewing this topic.

Re: Position Errors Only on Diagonal Moves
« Reply #10 on: January 14, 2015, 01:45:27 PM »
OK next test Does it cut exactly the same IF you reverse the order of cut From  CW to CCW. IS the offsetting of the cut the same ??

(;-) TP

Terry,

Good question!  I think we tried that, but not 100% sure.  I'll make sure we try that.

Regards,
Ray L.
Regards,
Ray L.
Re: Position Errors Only on Diagonal Moves
« Reply #11 on: January 14, 2015, 01:46:47 PM »
If it’s any help to the discussion I have just been and cut two 50mm squares, one on the X-Y axis and one at 45 deg. They were both cut ‘on the line’ with a laser so turned out 49.4mm x 49.4mm but they both measure identical.

Tweakie.


Doesn't surprise me.  I'm sure this is something in this machine, or Mach3 install.

Regards,
Ray L.
Regards,
Ray L.
Re: Position Errors Only on Diagonal Moves
« Reply #12 on: January 14, 2015, 01:47:40 PM »
Is the 0,0 part position at the center of the square ? or elsewhere ? (at a corner)
Might try it both ways just to see if there's a difference there.
I would, but can't right now.
Russ

It's generally been off to the left, but perhaps not always.  I'll have to check. 

Regards,
Ray L.
Regards,
Ray L.
Re: Position Errors Only on Diagonal Moves
« Reply #13 on: January 14, 2015, 02:38:26 PM »
Well, I am the friend that's been having issues. Here is the thread on cnczone: http://www.cnczone.com/forums/showpost.php?p=1624744 this thread documents the tests I have run now.

The code is generated in HSMXpress. As Ray noted, it has been hand checked. I have generated code that had the origin:
  - in the center of the square.
  - at points below and left of the square
  - at points above and left of the square
  - at points below and right of the square
  - at points above and right of the square

In all cases my 90 degree squares (sides parallel to the x and y axes) come out perfect. My 45 degree 1" wide squares (sides are 45 degrees from the x and Y axes) are always coming out .956 in one direction and 1.042 in the other.

Note that I set up dial indicators and did testing for lost steps as well as for backlash and neither are occurring.

Not on that thread but another data point: I took the control computer from one of the CNC routers in my shop and put it on the mill. That Mach 3 installation functions perfectly on the CNC router. I copied over the mill XML profile and ran the test again. It came out with the same dimensions.

Re: Position Errors Only on Diagonal Moves
« Reply #14 on: January 14, 2015, 03:17:31 PM »
The resultant box cut on the diagonal acts like it is a mechanical backlash problem in one axis only.
Also, if there is a mechanical problem, it cannot cut a perfect circle.
The problem may only show up when both axis are under load, versus the cutting the box with sides parallel to x and y.
Also, check the gibs in the head, using a long bar lever. If the machine is new, something may have been overlooked
in the assembly, like final clearance adjustment.

John

 

Offline ger21

*
  • *
  •  6,290 6,290
    • View Profile
    • The CNC Woodworker
Re: Position Errors Only on Diagonal Moves
« Reply #15 on: January 14, 2015, 04:16:50 PM »
Quote
I copied over the mill XML profile and ran the test again. It came out with the same dimensions.

Then create a new .xml from scratch and try it.
Gerry

2010 Screenset
http://www.thecncwoodworker.com/2010.html

JointCAM Dovetail and Box Joint software
http://www.g-forcecnc.com/jointcam.html
Re: Position Errors Only on Diagonal Moves
« Reply #16 on: January 14, 2015, 04:34:38 PM »
The resultant box cut on the diagonal acts like it is a mechanical backlash problem in one axis only.
Also, if there is a mechanical problem, it cannot cut a perfect circle.
The problem may only show up when both axis are under load, versus the cutting the box with sides parallel to x and y.
Also, check the gibs in the head, using a long bar lever. If the machine is new, something may have been overlooked
in the assembly, like final clearance adjustment.

John

 

The machine is about 1 year old. To test backlash under load, I ran the square test with a engraving bit going only .01" deep. Just enough to score the part. The spindle load meter was at 2% the whole time. It still came out the same.

I first thought it was lost steps or backlash. I measured my backlash according to this video: http://www.youtube.com/watch?v=buXHZ_McbOY and I got less than .001" on each axis. Even if there was backlash due to load, the square is off by 0.042" in each direction, which is at least 10x the amount I would reasonably expect. I also did extensive testing for lost steps and my indicators read no steps through the entirety of my testing.

My next steps for testing will be:
  - cut the square backwards and see if it's different.
  - swap the X and Y servo drives and see if that reverses the cut.
Re: Position Errors Only on Diagonal Moves
« Reply #17 on: January 14, 2015, 04:37:29 PM »
Quote
I copied over the mill XML profile and ran the test again. It came out with the same dimensions.

Then create a new .xml from scratch and try it.


In a separate test, I had the manufacturer send me a vanilla xml they use for the machines and I tried that. I also tried redoing it from scratch. I tried with just the PP. I tried with a UC100 motion controller. The square came out off by the same amount for all of them.

Offline Hood

*
  •  25,856 25,856
  • Carnoustie, Scotland
    • View Profile
Re: Position Errors Only on Diagonal Moves
« Reply #18 on: January 14, 2015, 04:51:11 PM »
Have you tried it with a G4P1 at the end of each move?
Can you monitor the encoder position in the servo drive software? (not sure what drives you have)

Hood
Re: Position Errors Only on Diagonal Moves
« Reply #19 on: January 14, 2015, 05:16:56 PM »
Ray said this was a bed mill. Is it a commercial metal cutting mill ? Or more of a hobby level type ?
 
Just curious.
Russ
« Last Edit: January 14, 2015, 05:48:40 PM by Overloaded »