Hi, after the recent purchase of a Zenbot, Mach3, and LazyCam I discovered a problem of a accumulating positive shift on all axis that was not being displayed on the DRO’s of Mach3. This was really apparent within projects containing multiple circles being cut around a central point.  After trying  to solve the problem using the many setting available within Mach3 and not being able to solve the problem I was able to correct the problem by writing a macro.  Thank you ArtSoft for providing the training videos.  Using the macro has greatly increased the accuracy of the machine. If any one knows how to solve the problem without using the macro please let know.  
Best Regards

lokey, I may be wrong but it sounds to me like your steps per aren't set right.

Brett

Hi, I am new to CNC and I tried many times to correct the problem using that method. I used a dial indicator. I would set code to move 2 inches and it move 2 inches. When I repeated the process there was a accumulating positive shift of  0.003 after each test run that was not showing up on the DRO's. When I use the macro the shift does not occur.
I will keep trying to correct the problem using your suggestion.  It would be nice not to use the macro, shorter cut time. Thanks for your feed back.
Best Regards

Is it possible this is to do with active high or low on the step or dir  pin not being compatible with your drivers?

Gaining or losing a step on each direction change?

Greg

Hi, I tried active low and active high, still had the same problem. I ran test code of a series of circles around a central point without using the macro and pressed goto z to return to the start location and it was off to the positive on the x and y  by a noticeable difference. I ran the same code using the macro and it returned to the correct start location. The problem appears every time the axis moves and there is a accumulating shift of 0.0015 to the positive that does not show on the DRO‘s. There maybe a setting within Mach3 to correct the problem, I read through the doc files but I am unable find it. I will keep trying and thank you for your feedback. Best regards

Art, the author of Mach3 is quite clear that the DROs  show only the pulses that have gone out the printer port.

If the DRO shows it has moved one unit then the PP has put out one unit worth of pulses. You will find that the problem lies somewhere after that fact.

Most likely mechanical but may be electrical.  Start by halving the rapid speed and acceleration rate and retest.

Greg

Hi, I try the suggestion and there is still a positive accumulating shift of 0.0015 after all axis movement. I am new to Mach 3 and if there are any other possible solutions to the problem please let me know. I attached the part .dfx file, it is the only moving part of the project and needs to center.  Even with the macro the inner circles cut fine but the outer circles are offset.
Best regards

When you say you have a shift of .003 are we talking inches and is the position getting nearer to the home position every run?

Graham

Hi, yes inch’s.  I am using a Zenbot with Mach3, LazyCam, and TuboCad.  In the system I found there is a accumulating positive shift after each axis movement that doesn‘t show up on the DRO‘s. . I am new to the software and there maybe a setting to deal with the problem but I am unable to find it. The problem becomes really apparent with a project that include cutting circles around a central point. The last outer circle would be so far off center that the part would be useless.
   I was able to write a macro that solved the problem. I have to run the macro after each axis movement. Because the Zenbot has drive belts the macro works really well and it has increased the precision of the Zenbot to a surprising level. Great bang for the bucks when your just starting  out.  I would not use the macro if the machine had ball screws.
    If you know of a solution to the problem without using the macro please let me know. Thanks for feedback and best regards. 

 In the system I found there is a accumulating positive shift after each axis movement that doesn‘t show up on the DRO‘s.

Does this lost position happen on every axis or only one?  Logic says that it must be one of two things.

First is mechanical slippage.  Somewhere between the stepper shaft and the axis.

Second is lost steps on the stepper.  This can be mechanical load being beyond the steppers capability.  Maybe a tight spot.  Maybe acceleration and or rapid too fast.

What stepper motors, driver, power supply are you using?  Are you using a break out board?

After ruling out mechanical issues cut the acceleration and rapid speed in half and see if that makes a difference.

Greg