Hi, I tried the suggestions and still have the problem. The accumulating positive shift occurs on all axis. I did notice that after performing G28.1 code that some axis do return to zero and then display +0.0009 or -0.0009 on the DRO's without any additional code. That is indicating that it is software related and is why I had to include so many reset DRO's to zero commands in the macro.
I am not software engineer but I am thinking that it maybe a truncation issue. I am still searching for a solution that does not require the using of the macro. If other possible solutions to the problem come to mind please let me know. Thank you for your efforts and best regards.

Hi, I tried the suggestions and still have the problem. The accumulating positive shift occurs on all axis.

OK cutting acceleration and rapid in half did not fix it then cut it in half again and retry.

You did not say what drivers etc you are using.  The drivers may need a longer pulse.

Also try "Sherline mode"

Greg

Hi, the system is a Zenbot 12x16 CNC router.  I tried all the above suggestions and the problem remained un-solved.
I noticed that when I used 28.1 G code that the DRO's would not reset zero but would reset to a + or - 0.0009. I rewrote the macro to adjust  for the DRO display error and run the macro after each chain is cut and the machine now cuts the project very well.
The problem could be a truncation issue with the software. Thanks to everyone for the support.

Is there away to change the directions of the cuts within LazyCam? If anyone knows please let me know.
Best regards.
 

Lokey you need to get past thinking the pulses are not lining up with the DROs

The DROs only count the pulses as they go out the LPT.  They do not report pulses that Mach thinks it has sent out.  Only pulses that do go out.

The problem exists somewhere after that fact.

If after cutting a job the DROs return to zero and the machine is off position then you have lost steps for whatever reason. 

Greg

Hi, I understand what you saying. The DRO's report what has been sent to p-port. After I use a 28.1 G code command the DRO's should re-set to zero. They don't, they re-set to a + or - 0.0009.

That will depend on what steps per unit you have for that axis.

If it a nice round number like 1000 steps per unit the DROs will read zero.

More likely you have a number like 567.689 steps per unit.

In the background Mach does all its calculations to ten decimal places.

My router has 106.7653 steps per mm and it will cut complex jobs over many hours and return to zero within a thou.

The software will not accumulate a measurable error after every cut segment you must look beyond that point.

It might be electrical, pulses may not be getting to drivers reliably, drivers may be missing pulses.  You still have not told us your driver, power supply, BoB etc setup.

Or you are missing steps because of performance tuning or mechanical issues or even mechanical slippage.

Greg

EDIT:  This is a recent purchase.  What have the people that you bought it from said about this.

Also what is the rapid speed and acceleration set to?  And what is the lowest values you have tested it at?

Hi, the step per unit are 1112 as recommended by the manufacturer. After I use G-code G28.1 X Y or Z 0.0015  the DRO‘s do not reset to zero, but reset a + or - 0.0009.. 
I am trying to look beyond the macro solution.

 When I tried the calibration axis feature the circles would cut as ovals. Motor tuning are set to spec’s. I checked the machine for possible mechanical issues and was not able to find any. When I cut a hole for a bearing on a project it is very accurate. The problem only occurs after movement to the next cut location.

 The dial indicator I use for testing measures to 0.0005. The control box came with the Zenbot, if it was missing pulses would it travel less and stop short.?

I really appreciate your efforts and will continue to implement your suggestion to try to find a solution. Thanks again and best regards.     

 Motor tuning are set to spec’s.

You did lower rapid and acceleration as I have suggested about three times, haven't you?   

Let me know what settings are spec and what lower settings you have tried.

When I cut a hole for a bearing on a project it is very accurate. The problem only occurs after movement to the next cut location.

This is a strong indication that lowering the rapid and acceleration or "tuning them" will make a difference.

While it is cutting the hole it is travelling at cut speed, as set in gcode.

Then when it rapids to the next location is when it is losing its position.

Greg

Hi, I posted a jpeg of the tuning page. If this is not the info you are requesting please let me know where I can find and set it.
I did try lower setting.

Try setting Velocity to 100 and acceleration to 10 and try your cutting job.

Do that setting for each axis and save axis settings each time.

Let us know if that improved position error.

Greg