Hi.
I have just finished retro fitting cnc to my Myford super lathe. Every thing runs OK, but I am unable to calibrate the Z and X axis to bee accurate. I have managed to get them nearly correct by trial and error.
The lathe have imperial screws (8 and10 TPI), but I am working metric. The stepping motor is standard- 200 step pr turn and is micro stepped to 1600 steps. And the reduction from the motor to the screw is 1 to 2. Folloving the instruction in the manual I com up with this numbers: For the Z axes s 1007.874 and the X axis 1259.84252. Putting this number inn the box "Steps per" in the Motor Tuning dialog box do not give me the right movement of the saddle and slide. What am I doing wrong?
In Mach3 Mill there is a utility to set this number automatic, - is there something like this available for Lathe as well?
Hope some can help me out here. please.

Thanks

Johs. Line

How far out is it?
Have you definitely got Mach set to metric from Config menu then set native units?
Your calcs seem fine.
You should be fine loading a mill screen and get the calibration done via the utility and then set back to a lathe screen but its not the method I like as calculating will be as accurate as your hardware, doing the auto is only as accurate as your measuring.
Hood.

Thanks Hood

Since I posted the question I found a calculation spreedsheet on this side and it stats that I had a right calc.
See below. (I do not know how to insert a file to this page).
I do not remember how much of but it was quit a bit - something like in the x direction 5mm instead of 10 and in z 30 instad of 10.
Of to bed now,- check it to morrow

Metric               
Required inputs               
   Stepper Motor       Deg/step -    1,8   
          Steps/rev -    200   
   Micro Stepping      Pulse/step -    8   
         Pulse/rev -    1600   
   Gear Reduction      Stepper teeth -    12   
      (Enter zeros for      Lead screw teeth -    24   
      direct drive)      Multiplier -    2   
   Leadscrew      Pitch (mm) -    3,18   
         Thread starts -    1   
         Lead (mm/rev) -    3,18   
   Result      *Steps per mm -    1007,87   
         Resolution (mm/step) -    0,000992   
               
               
    Input:        Result:      
   Feed - mm/min    2500   pulse/sec =   41994,75   
         mm/sec =   41,67   
         stepper rpm =   1574,8   
   Stepper RPM   500   mm/min =   793,75   
         mm/sec =   13,23   
         pulse/sec =   13333,33   
   Pulse/sec   13333,33   stepper rpm =   500   
         mm/min =   793,75   
         mm/sec =   13,23   
   Distance vs.   3200   steps = 3,175 mm      
   Steps   1   mm = 1007,874016 steps      
               

Sounds like you may not have the microstepping set on your drives to what you think, best double check that. For the X it cold be the difference betwen Radius mode and Diameter mode though.
Hood

Well I had to check before bed.
You are correct it is the radius/diameter thing. When I checked with the correct numbers the Z was moving correct but the X axes was moving only half the distance, the dro in "Programs Coordinates" showed the correct number, but the "Machine Coordinates" showed half the value. This was also the distance the slide had moved. I was working in diam. Changing to radius the movement and the dro was correct!
Is this the way it is suppost to bee?
Thanks Hood, I am sorted out now and can sleep happily to night.

Yes the machine coords always work in actual movement but if in Dia mode your DROs show double movement. I prefer Dia mode myself.
Hood