That is on possible culprit, epoxy will wear and also heat up from repeated back´n´forth motion. Heat will make it soft / flexible and cause binding. Epoxy is a terrible media for that application.
Get a cheap one of Delrin/POM and it will be much better suited.
That is regardless wether it is the epoxy nut that is causing you problem or not.
i Have been looking all over to get the nuts for acme rod 5/8 inches and unable to find one.
Does anyone know where i can get them ?
If you can’t find one, make one 
i did and its not working
Unless you I misunderstood you you mentioned you had it machined out of epoxy.
Try again, but use Delrin (DuPont brand name) or POM/Acetal which is the same more or less.
At least we’ve found the probable source of the issue.
Unfortunatly not… problem still there, im really wondering it’s a motor tuning issue. I can’t get it tuned right tried a lot of tune and on top of that im not even sure my dip switch are right
Is there any way i can found the right velocity and accel by making a calculation of amps and step angle of the motor. How im suppose to know that my motor is well tune
You made a new nut for your 5/8" leadscrew?
No. Every machine is physically different. Those values will be specific to your machine.
As someone mentioned earlier, reduce them and test again.
i actually found a metal that fits perfectly…we actually use these for wood tighthening
OK now i have switch motor from z axis to x axis and still have the same problem
i have done everything even removing the z front panel and running a dry program for 5 mins and still came up with a lower calibration of 0.0545 inches.
I even change several time velocity and acceleration with no change.
I also change the voltage on the power supply and that didn’t help either.
i am out of solution if someone can help me that would be very well appreciated.
Cheers
Can you post some pictures of your controller and machine for us?
Can you also post the GRBL settings currently used?
There is also the chance of “false steps” being picked up by Z, due to poor grounding, bad wire, defective driver or just bad luck.
i hope this help
could a bad ground connection on my Y axis driver interfer with my z axis ?
