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Lead screw pitch off?

Discussion in 'General Talk' started by Matt Knudstrup, Jan 31, 2017.

  1. Matt Knudstrup

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    Hello everyone, my first post here.

    So I received some 8mm lead screw about a month ago from the Openbuilds Parts Store to build a CNC Ox Metal. I have the machine all together now and am setting up parameters, etc. The problem I'm having is that I'm getting just over 517 mm for 64 turns of the lead screw and it should be 512 mm. I've checked it many different ways and counted one rotation at a time at the stepper just to be sure. Both the X and Y axis are off by the same amount. That is a lot off and I can almost compensate for it in the Grbl settings but probably not 100% accurately. I'm just wondering if it is typical for lead screw to be so far off? Has anyone else seen this?

    Thanks,
    Matt
     
  2. Matt Knudstrup

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    After doing some further reading, I can get things pretty accurate by setting $100 and $101 to 197.8. I didn't realize you could use decimals for this setting. I still think it's a little weird for the lead screws to be this far off and I can't think of any reason they would be off at all.
     
  3. Rick 2.0

    Rick 2.0 OpenBuilds Team
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    That's only a 1% error, something which is probably considered within mill tolerances. You can probably get more accurate screws but the question would be at what price.
     
    Jestah likes this.
  4. David the swarfer

    David the swarfer OpenBuilds Team
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    Even industrial ball screws have to be calibrated. Most industrial controllers allow for a table of correction factors to be entered to cater for cyclic errors in the screws. I.e., this is not unusual, just follow the calibration HOWTO Calibrate your CNC Machine for MACH3 or GRBL
     
  5. Matt Knudstrup

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    Ok, thanks guys. I'm pretty new to this stuff and had no idea but I'm up and running now. I guess I need to go get myself a real nice ruler. Now if I could only get those darn limit switches to work on my el cheapo Arduino controller. I know it needs some sort of filter on the inputs but I haven't seen a real solid solution yet. Time for a new post :)
     

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