Hi All

Recently I have built a cnc router and am having an issue with 'drifting' + in the X axis and - in the Y axis. If I calibrate and set the steps per inch with a dial indicator and tell it to move 1" it moves .990 and I enter that number and click OK. Mach3 tells me how may steps per unit it is using and I accept the value. When I then ask it to move +X 20" it moves +20.010". When it goes back to home the X DRO is 0.000 but the location is +X 0.010 if i repeat this the next move goes to +X 20.030" and so on. At the end of the test the DRO's are correct but the location of home is +X0.040. This same thing happens in the Y axis.

Long program run, bigger drift. Any ideas?

PC running windows XP
The computer is dedicated to Mach software only.
All axis use stepper motors.

I presume its steppers so what is the microstepping of the drives?
What if any gearing do you have between motors and screws?
What is the pitch of the screws?
Hood

Thanks for the help

All are 1200 oz/in cables with shielded 16AWG
No gearing and all couplings tight
I think the screws are 8 turns per-inch (I can check Monday and let you know with the micro stepping)

Parnell

Still need to know what microstepping the drives are but say it was set to 10 then your steps per unit would be
200 steps per motor rev x 10 microsteps  x 8 turns for 1 unit (inch) 16,000 steps per inch.

Hood