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Ox accuracy suffering. Thoughts? Ideas?

Discussion in 'CNC Mills/Routers' started by Cody Alward, Feb 19, 2016.

  1. Cody Alward

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    I've been running my ox now fairly hard for around 6 months 3 to 5 nights a week. First issue I was having as loose pulleys. Problem solved. It continued to run very well up until recently. It has been acting up and I haven't quite tracked down the problem. Hopefully someone can help.

    My OX is plain-Jane just a little bigger 1500X1500
    Gecko G540
    Mach3
    cheap ebay cnc motor kit from Longs-motors(1 amp nema 23, 1.8 degree )
    power supply that was provided 24V 4.5 Amp
    I usually cut from 100 to 140 in/min

    I'm by no means expecting super precision. I can accept some flex and runout but the problem I'm having is measurement inconsistency. Lately I've been re-calibrating steps in mach3 and getting variations of readings from .015 to as much as 0.033 running recalibrations(0.8 in movements) back to back. It has just recently gotten this extreme.

    When I'm resetting motors to dial indicator motors jump forward or backwards .001 to .007 almost as if its finding the closest step after I stop movement and they appear to be humming more than usual. Am I wrong to think that these cheap motors are finally giving up on me. Also, this is my first belt driven machine, is their a way that belt tension is causing these variances?. I don't have a problem buying new motors or even switching to a different type of linear motion. Iwould just like some insight from some of the old Salts on here before I decide which way to go. Better quality motors, double belts, ballscrew, rack and pinion? At this point just looking for some insight.
    Cody
     
  2. Joe Santarsiero

    Joe Santarsiero OB addict
    Staff Member Moderator Builder

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    Hello Cody,

    My initial thought on this focused on the 1amp motor rating and the fact that you have some experience with the machine. It's possible you are out growning the stepper motors for the feeds, speeds, tooling and material that you're adapting to. You have a good driver, but inferior PS and motors to match (no offense). Personally, I'd go 48v and start looking at 3 - 3.5 ampish/higher torque motors.. as it sounds like you might be losing steps and possibly more while approaching your comfort zone. There could be a number of other things causing your issues, but still, with that driver I'd be utilizing it way more than you are now (which isn't much). I say update those (less than $200) then work through any mechanical weaknesses such as drive, guide and deflection.
    Just my immediate thoughts.

    Joe
     
    GrayUK likes this.
  3. Cody Alward

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    Joe,
    Thanks for the input. No offense taken, I realize the motors and power supply really aren't that good. Getting the table put together was the biggest hurdle. Eyebrows of the Mrs. aren't raised nearly as high if I'm just swapping parts. One thing that 5 yrs of marriage has taught me is, as long as things are the same color and similar size (ie. fishing rods, lures, reloading equipment, stepper motors ect.) very few, if any, questions are ever asked.

    This has been somewhat of a test to see the ability of the "cheap" parts and I was just looking to pass on some info for other builders toying with the idea of the ebay kits. Controller lasted about 3 weeks,(Gecko g540 was huge improvement) motors are kinda lasting(they still move)

    Is their a good supplier (or motor) you could recommend for 3 to 3.5 amp motors and a power supply(amperage?) to match? I upgraded driver and I would rather buy quality motors to match so I won't likely have this problem again for some time.
    Thanks, its relieving to know that I was leaning towards new motors and power supply anyway
    Cody
     
  4. Metalguru

    Metalguru Master
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    Cody:

    The NEMA 24 motors and power supply in the Openbuilds store are pretty good, and motors are rated at 2.8A. I run mine at 3 amps with no problems.
    Power supply has enough power (14.5A @24v, I think) to run 4 motors full bore all at the same time. You can get the whole set for around $150.
     
  5. Cody Alward

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    Cool, thanks for the help. I appreciate the input
     
  6. Metalguru

    Metalguru Master
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    PS: Cody you sneaky bugger... You've discovered the "looks the same" rule after only 5 years of marriage -

    It took most of us much longer 8D
     
    GrayUK likes this.
  7. Giarc

    Giarc Master
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    Another option is money laundering. Every time you get groceries, or do other miscellaneous shopping, use the debit card and get cash back. Don't forget to lose the receipt. $20 here and there can add up quick. ;)
     
    Metalguru and GrayUK like this.
  8. Metalguru

    Metalguru Master
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    Great idea Giarc. What a devious bunch... Money laundering indeed! Maybe we should start a new thread...
     
  9. Jimmybuckets

    Jimmybuckets Veteran
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    Couple easy things to check before spending $$$. Cut some small squares and circles. Reduce step down and cutting speed. Try one run with climb cutting only and then the second run with conventional cutting. Trying cutting your speeds in half and use a step down of 1/8"...see if your problems get better and note...climb vs conventional. You may just be running up against the mechanical limits of your machine. Just my 2 cents.
     

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