Machsupport Forum

Mach Discussion => General Mach Discussion => Topic started by: KE5OTO on February 23, 2014, 06:19:47 PM

Title: DRO doesnt match gcode move
Post by: KE5OTO on February 23, 2014, 06:19:47 PM

I input as follows
go
x -1.000
y -1.000
z -1.000

And the Dro reads
x -0.9984
y -0.9970
z -0.9997
is there some way to correct for this?

Title: Re: DRO doesnt match gcode move
Post by: RICH on February 23, 2014, 06:43:07 PM

Check for backlash and also make sure the steps per are accurate.
Movement is only as accurate as the components that mechanicaly drive it.
RICH

Title: Re: DRO doesnt match gcode move
Post by: KE5OTO on February 23, 2014, 06:53:53 PM

my components are not accurate by any means but i do not understand why if i tell the axis to move one inch the dro doesnt read one inch. I dont have encoders so im not sure why the difference?

Title: Re: DRO doesnt match gcode move
Post by: KE5OTO on February 23, 2014, 07:37:17 PM

Let me clarify. I do not have an external DRO on the machine I am talking about the computer screen readout in Mach 3. Hope this makes more sense.

Title: Re: DRO doesnt match gcode move
Post by: Overloaded on February 23, 2014, 08:19:41 PM

That might just be the resolution of the axis's.
How coarse are the "Steps Per" settings in Motor Tuning ?

Russ

Title: Re: DRO doesnt match gcode move
Post by: KE5OTO on February 23, 2014, 08:27:05 PM

120 - 122 depending on axis. i am using some old ibm nema 23 motors with delrin ball screws that are pretty aggresive 1.75 inch per turn

Title: Re: DRO doesnt match gcode move
Post by: KE5OTO on February 23, 2014, 08:42:20 PM

I think you hit the nail on the head! I changed the resolution to 200 and got a lot closer consitantly. when my new motors and lead screws come in i suspect it will get much better!

Title: Re: DRO doesnt match gcode move
Post by: Overloaded on February 23, 2014, 09:14:53 PM

Yes, that is quite coarse.
Setting a higher micro-step will help a bit, If your drives have that capability.

Then adjust your "steps per" accordingly of course.
Russ