Inconsistent DRO Values. HELP Please!!

[willio]

I have an Eldorado with the full CNC package but not with the ball screws.

I am using Mach3 and trying to set up the motor tuning values.

I have them dialed in pretty close, X and Y are at 40,000 and Z is at 60,000.

I reset the DRO put in a basic G-Code movement (g01z.1) and the machine moved to the location. The mach 3 display shows a move of .1 but the DRO shows a move of .0923.

I do this over and over and every time I get a different number. same thing happens with the X and the Y. .0923, .0922, .0898, .0998 etc.

I am not sure if the backlash has anything to do with this because I am always running them in the same direction so the back lash should have no effect.


Any ideas?

[instructor37]

Willio,
Without knowing the model and type of DRO, I would suggest that your first step would be to test the DRO itself for any problems. Use a dial indicator on tha carriage and compare the readings to the DRO. Watch for changes in the DRO reading after you stop the motion which would indicate some binding in the scales.
If your DRO is OK, then look for ;
1. Loose gib adjustments which will cause the table to rock from side to side
2. Looseness in the brackets that hold the brass acme screw nuts
3. Inspect the thrust bearings on the lead screw for any contamination or looseness.

[dgapilot]

I noticed that your G code was showing the Z axis. On the Elderado, the Z is using a gear set up with a spring return. Repeatability of this is not real good. With the Z ball screw it is much better.

Use the info from Mach on set up. Use a dial indicator and run an inch or more so you have a reasonable repeatability. Once you figure out the error, then make an adjustment of the steps so you actual command will give you the same movement. None of my 3 axis have an exact number of steps. Error in the lead scres and God knows where else, but once you figure out the number of steps that get you to the appropriate dimension then life is good. Don't think that X and Y will be the same, because they won't. And like I said, Z isn't very repeatable given the method used without a ball screw. (move the quill down some under cnc control, then push up on the quill. It will most likely move up about .050" due to backlash in the gear set up.) If you are milling and need a constant depth, lock the quill even with CNC.

David

[willio]

You guys are the best!

Now on to the next 47 problems...