Machsupport Forum
Mach Discussion => General Mach Discussion => Topic started by: menglor on October 03, 2013, 10:07:03 AM

Good day,
I have question that I cant seem to find anywhere, I am sure its something I am doing, but You guys are the people to ask :D
so, I am trying to set my soft limits, (in metric) and I suspect my bed can move about 1000mm left or right..
but when I do so, my DRO says its moved 4.19
I suspect that the scale is wrong, or its using imperial to measure.
I am pretty sure its moving about 710 inches, but I am pretty overwhelmed with all the options, I was hoping you guys could help me out here.

You need to set the steps per unit for your motors in Motor Tuning. The value you have there will depend on the type of motor, if servo you need to know encoder count, if stepper then you need to know whether its a 1.8 or 0.9 degree motor (1.8 most likely) also the microstepping of the drive. You also need to know the pitch of the ballscrew and whether you have any gearing between motor and screw.
If you let me know the answers to the above I will show you how to work out your steps per unit.
Hood

Very cool, thank you.
here is the information as I have it :
My Ball screws's are this kit :
http://www.cncfusion.com/minimill1.html (MiniMill CNC kit #2  with XYZ BALLSCREWS)
(Ballscrew kits use 5/8" Thomson ballscrews with a .200 pitch. Here is a link to the Thomson catalog page with detailed information on the ballscrews.)
and the Stepper motor kit I bought is :
http://www.automationtechnologiesinc.com/productspage/g540steppermotorkits/g540381ozin48v73a
motor specs
(3 pcs NEMA23 KL23H2100354B(1/4” Dual shaft with a flat) 381 ozin)
KL23H2100354B Can be used for G540, G251, G250 or any other drivers
381 oz In. Hybrid Motor
1.8° /200 Steps Per Rev.
3.5 Amps Current Per Phase Inductance
2.8 mH 4wire Bipolar, NEMA 23 Frame  See more at: http://www.automationtechnologiesinc.com/productspage/nema23/nema23quarterinchdualshaftwithaflat381ozin#sthash.9Fcb8Roe.dpuf

Ok so you have screws with 5 turns per inch (0.200" pitch)
Your motors are 1.8 degree so 200 steps per rev
your drives are Geckos and they have a fixed 10x microstep.
So steps per unit (assuming you have directly coupled) are
200 x 10 x 5 = 10,000 steps per inch
Hood

thanks, I have added that to my config.
although, its moving the table around a lot nicer, it DRO still doesnt seem to be displaying the right info.
I am set for Metric, and when I move the table say "1000mm" to the left, on the DRO its only displaying +1.5 (i am assuming this is still in inches?)

Ok sorry I thought you were set up in Imperial units. the number for steps per mm would be
10,000/25.4 = 393.7007875
Hood

Thank you very much, I know understand a whole lot more of that screen, ya, plugging in the smaller number definitely makes the DRO display bigger numbers.