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Jog resolution HELP please!

Discussion in 'Controller Boards' started by Bernie Jones, Jan 22, 2016.

  1. Bernie Jones

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    Hi all, fairly new to the CNC world, but have an HND in tron related stuff.

    Equipment: standard 750x750 Ox. Xpro v2 controller set to 1/8 micro. 24v PSU. Universal g code sender.

    Problem: dial indicator on x and y axis when jogged at 0.1mm is inconsistent. For each jog, the dial indicator appears to hardly move for the first 2 jogs then 'catches up' and moves 0.3mm. This is pretty consistent on the x and y axis. The z axis (acme screw) is spot on 0.1mm per jog.

    If I jog at 0.3mm per jog, all appears ok, if just a little inconsistent with each jog.

    My belts (single) are tight (twang!) and I'm pretty sure there's no other play.

    Any ideas? Should I try 1/16 micro to improve resolution but lose torque?

    Inputs or ideas gratefully received.
     
  2. Mark Carew

    Mark Carew OpenBuilds Team
    Staff Member Moderator Resident Builder Project Maker Builder

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    Hello Bernie welcome to OpenBuilds!
    I have had a similar experiences with loose pulleys, be sure to check that the pulleys are one with the shaft if there is any slippage at all this can happen.
    Hope this helps
     
  3. Bernie Jones

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    Thanks Mark. I've checked the pulleys and they are solid with the shafts on both x and y. I also took the belts off to check for any mechanical issues with the axis.. All looks and feels ok. On the basis that a 0.3mm jog works ok, I can only assume it's a driver/software or controller issue. I'll try the 1/16 steps just for information I think.
     
  4. Mark Carew

    Mark Carew OpenBuilds Team
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    good idea Bernie
     
  5. Bernie Jones

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    Justin, thanks for the confidence booster! You may be right. I haven't cut anything with the machine yet, so maybe I should be focussing on the practical end game rather than attempting to seek theoretical perfection in set up. The machine itself zeros very well and returns to zero spot on (dial indicator) so maybe this is all good enough..... After all, I'll be cutting wood mainly... Not space shuttle parts.
     
  6. Bernie Jones

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    Yes. All relative! I did actually switch to 1/16 stepping and it has improved the jog resolution. I now get quite nice measurements especially at 0.15mm jog. All good enough... Especially when I'll probably be mostly making wooden signs... Lol!
     
  7. David the swarfer

    David the swarfer OpenBuilds Team
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    leading on from calibrating
    OpenBuilds OX CNC Machine | Page 57 | OpenBuilds
    I postulate that your minimum jog step should be set to your exact mm/step size.
    You can never jog less than that anyway, so you may as well take an entire known step.

    so from the example in the linked post, at 16x microstepping
    mmPerStep = pulleyteeth*beltpitch / stepsperrev
    for example 20 * 3 / (200*16) = 0.01875 mm/step

    so if you set your smallest job step to be 0.01875mm you should see that on the dial test (well, technically you will see that as an average movement per step since microstepping is not linear nor as accurate as the adverts will want you to believe).

    I do recommend that you stick with 1/8 microstepping
    20*3/1600 = 0.0375 mm per step.
    I doubt you an even feel let alone see that size step in the workpiece (-:
    and you get a lot more torque compared to 1/16 stepping. more torque means you can rapid, and cut, FASTER.
    and, in fact, more accuracy in the microsteps.
     
  8. Bernie Jones

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    David, many thanks, good info. If I can achieve 0.1mm in a practical application (I'm a woodworker!) I'll be delighted.
     

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