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Mach3: Unexpected Response for Steps per Inch

Discussion in 'CNC IN THE HOME SHOP' started by angelfj1, Aug 2, 2017.

  1. angelfj1

    angelfj1 United States Active User Active Member

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    Hello:


    Although I have completed the CNC conversion, I'm really having fits with the motor tuning and axis calibration. Something very strange is happening. I would like to take this real slow because I have limited experience with Mach3. I will list some basic facts regarding my cnc conversion.

    My machine is a Grizzly G0704. Although this started out as a Hoss Phase II project, I changed my plans and purchased a pre-engineered kit supplied by David Clements, aka ArizonaVideo99. I had the saddle machining done by a local shop. They also did the oiling groves. Everything came together nicely.

    Details
    The ballscrews/nuts are metric - 5mm pitch
    The steppers and other electronics are:
    2 - KL23H2100-50-4B, 570 Oz-In (NEMA 23, for X & Y axes
    1 - KL34H295-43-8A,960 Oz-In (NEMA34), for Z-axis
    Drivers
    3 - KL-5056D Digital Bipolar Stepper Motor Driver, set for 1/8 micro-stepping
    BOB - C10, parallel port interface

    I'm using Mach3, running on Win XP. I currently have the evaluation (free) version, but intend to purchase a license as soon as I iron out the strange symptoms I’ve experienced.

    I have been able to get everything connected and responding to mach3. I can jog the axes.

    My problem started when I tried to use motor tuning.

    I set the X, Y and Z velocity and axxeleration very conservatively, 20 inches/min, and 3 in/sec/sec

    I calculated the steps per inch first before trying the Mach3.

    I did it like this:

    My stepper motors - 200 steps/rev
    Micro-stepping - 8 pulses/step
    So, 200 x 8 = 1600 pulses/rev
    no gear or pulley , e.g. N = 1
    ball screw - 5 mm pitch or 5/25.4 in. pitch = 5.08 TPI
    steps/inch = 200 x 8 x 5.08 = 8128.

    So, I entered 8128 for steps per inch.

    Then, I did an initial gib adjustment for the X-axis as suggester by Steve, Jumps4, ihis n YouTube video.
    I made sure that the X-axis gibb wasn't too tight.

    I set up a dial indicator to measure movement in the X-axis. For an input of 0.100, I was consistently getting .097. I did this several times and took an average. So, I went to the Mach3 settings page to use the steps/inch routine. I entered a value of 0.100 and the x-axis traveled .097. Then for "how far did you travel", I entered 0.097 and Mach3 returned a steps/inch value of 812.xxxxxxx, WHAT IS THIS? Since the X-xxis travel was only 0.003 short, I was expecting a number slightly more than 8128, maybe 8129 or 8130. But 812?????
    OK, I know something is crazy, so I answered NO to the recommended steps per inch, closed the program, turned off my electronics, turned off the computer and restarted. I repeated the routine in Mach3 settings for steps per inch but this time I got a different number but still off by an order of magnitude.

    Before I take any drastic steps, I wanted to reach out to others who have some experience with Mach3 issues.

    Many thanks,

    Frank
     
  2. RJSakowski

    RJSakowski H-M Supporter - Premium Content H-M Supporter-Premium

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    I ran Mach 3 for four years on my Tormach but never had to run the calibration routine as that had been done prior to shipment. I did have to run a similar routine on my lathe DRO though.

    Rather than proceed the way you have, you could divide your expected travel by the actual travel and multiply that by the calculated 8128 steps/inch. You should get 8379 steps/inch. Enter that in place of the 8128 entered previously.

    Run your expected vs. actual test again. To get a more accurate number, you should measure over a longer distance. I would use the longest distance that I could accurately measure. This will minimize any backlash/lost motion effects and round-off errors.

    Actually, I wouldn't expect the pitch on the ball screw to be off by that amount. That is a 3% error.
     
  3. Metal

    Metal United States Active Member Active Member

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    Oh you already found that screen

    Dont move such a small amount, move an inch or more.

    Any tiny amount of backlash and such is a larger percentage of the move the smaller distance you go, also make sure you are moving into the same direction

    Ex move left, then calibrate left, do not move right, then calibrate left

    if you go left-> right -> left without leading in you aren't taking backlash out of the picture, you set that up somewhere else.

    It may take a few calibrations to get it "just right"
     

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