Mach 3 DRO Bug ?

[UKRobotics]

Since recently calibrating my axes using the wizard in mach 3 my DRO's are not displaying what they are told to.

For example if i type g0 z-20 my dro for z shows -19.997. Why is this happening, do I need to worry ? Is this a known bug ? Seems like it might be a rounding error or something. Is there a way to fix it ?

Regards,

Dom

[ger21]

I'ts related to your steps per unit setting. I'm guessing that with your current settings, Mach can't actually get to 20. 19.997 is the nearest step. If it moved one more step, it would go past 20.

[UKRobotics]

I wonder if I can change my steps per unit very slightly to make the dro read right without harming accuracy. The calibration feature does end up with very long numbers after the decimal point.

[ger21]

Don't do that. Set the machine to cut accurately, and don't worry about the DRO. What are your steps/mm set to?

[UKRobotics]

804.8289738

[ger21]

Originally Posted by UKRobotics 804.8289738

For the Z? with that, it seems like it should display 19.999. Even so, I wouldn't worry about it. May be some rounding going on somewhere that I'm not aware of, but .003mm isn't much.

[UKRobotics]

I think that figure I gave you was for the X. I just picked the top of the list as an example.

I know the actual ammounts we are talking isnt much, but its little things like that which irritate me. After putting so much time and money into this retrofit, the least it can do is display the right digits on the dro :P

[ger21]

Originally Posted by UKRobotics I think that figure I gave you was for the X. I just picked the top of the list as an example. I know the actual ammounts we are talking isnt much, but its little things like that which irritate me. After putting so much time and money into this retrofit, the least it can do is display the right digits on the dro :P

It is. If 20mm = 16096.579476 steps, you have two choices. Move 16096 steps or 16097 steps. The only way to have the DRO's always be exactly what you want would be for your steps/mm to be 1000. That way 1 step = .001mm

[H.O]

Gerry is right here. The DRO shows where the control thinks it has put the machine axis. If the drive system (motor, encoder, screw etc) can't resolve to exactly the position the program tells it to it will stop as close as it can get without overshooting. If one more step means it will overshoot that step won't be sent out.