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  1. #1
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    Default Before I bin my whole control box...

    Hi all.
    Hope I'm posting this in the correct place. Newbie poster...
    So - I've built myself a 5 axis mill and am banging my head against an electronic wall. This is my 3rd build and up till now have been running 3-axis with G540's / mach3 with zero glitches.
    I know I shouldn't have skimped on the control gear, but hindsight being what it is... here I am.
    I thought I'd throw this out as a last resort before trashing the whole box and going with 2x G540's in parallel with an SS-02 Ethernet smoothstepper.

    Currently, the control box consists of:
    Novusun NVUM V2 USB 6 axis controller (the suspected culprit)
    6x TB6600 stepper drivers (one redundant)
    5x 1.9Nm Nema 23 Stepper Motor 3A (microstepped @ 1/8)
    Mach3 running on an i3 / 8gb ram / with nvidia GTX650
    USB interface is connected to a USB3.0 port

    Problem:
    I have the motors tuned perfectly (I thought). I can jog all 5x axes smoothly and run Gcode flawlessly.
    When I hit go to zero, sometimes, it will go to zero (all axes) but sometimes It will intermittently return to slightly off zero (0.0031 - working in mm) on some axes.
    I have 1605 ballscrews on X&Y and 1204 on Z.
    When the problem occurs (not always) it is consistently 0.0031 on both X&Y and consistently 0.0028 on the Z, leading me to believe this is fixable.
    By (almost) all measures, the thing works... if it wasn't for those darn decimal points.

    All cabling is shielded and I have triple checked all connections, reinstalled mach3, tried a different PC, tried 1/4 stepping and upped the amps on the TB6600s and a few dozen more things I could think of.

    All this being said, I suspect most of you will write off my novusun controller as cheap rubbish - or perhaps my TB6600s. And I shall take this on the chin, as I had suspected as such from the get-go.
    Unfortunately, I have invested considerable time and cash getting this enclosure off the ground, and I'd be forced to shed a tear as it tips sideways into the wheely bin.

    Oh, and I cant for the life of me, get the analogue MPG wired to the novusun NVUM to work - if anybody has some pics from a successfully wired one, I'd love to see them... before I toss the lot.

    Thanks!
    Giffster

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    Community Moderator ger21's Avatar
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    Default Re: Before I bin my whole control box...

    Is the error in the Mach3 DRO's, or have you actually measured it?

    If its the DRO displaying it, then it's likely just related to your steps/mm setting, with it be as close to zero as it can get within 1 step.

    Gerry

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    Default Re: Before I bin my whole control box...

    Hi Gerry.
    Appreciate the quick reply.
    The error is only in the Mach3 DRO.
    Steps per mm have been calculated based on 1.8deg per step, 1605 ballscrew (5mm per rev) @ 1/8 microstepping = 320 per 1mm
    But in theory, there are no encoders to provide feedback, so if mach thinks it sends an axis 50mm in one direction - then "go to zero" back the other way should result in 0.0000.... right?
    regardless of physical manifestation. (which appears to be accurate BTW)
    Thanks.



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    Community Moderator ger21's Avatar
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    Default Re: Before I bin my whole control box...

    You would think so. But this is a common thing with Mach3, and has no effect on precision or accuracy. When you goto zero and it stops at .003, it's still at 0.

    Gerry

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    Community Moderator Jim Dawson's Avatar
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    Default Re: Before I bin my whole control box...

    1/320 = 0.003125 so sounds like a processor rounding error.

    But seriously 3 microns? Just a 5 degree temperature change would cause more physical error than that.

    One guy I know put a piece of tape over the last 2 digits of his DRO screen because it was driving him mad.

    Jim Dawson
    Sandy, Oregon, USA


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    Default Re: Before I bin my whole control box...

    Thanks Jim / Gerry.
    I appreciate the input.
    Yeah, you're right 0.0031 is precisely 1 step isn't it...
    Instead of the tape, perhaps I can just reduce my DRO precision down to 2 decimal points so I dont have to look at it. Ha!
    I guess the process of machining has enough avenues for failure as it is without adding rounding errors at the control box.
    You are of course correct, 3 micron is negligible, and my gauges lack the precision to establish whether there is a physical step lost or not. Just doesnt sit nicely with me.
    Gerry, Interesting to hear that this is a common occurrence with mach3. I've never had this anomaly using geckodrives on similar machines with the same microstepping. perhaps the gecko profile just rounds them off to keep users like me happy.
    Thanks again for the advice.
    If anybody has any wiring pics or mach3 config advice on wiring an MPG direct to the NVUM V2 - I'd love to hear from them.
    pendant MPG is this one:
    https://www.ebay.com.au/itm/6-Axis-C...item1cd505f5ac

    Thanks!



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    Member CitizenOfDreams's Avatar
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    Default Re: Before I bin my whole control box...

    Quote Originally Posted by giffster View Post
    Yeah, you're right 0.0031 is precisely 1 step isn't it...
    1/320 is 0.003125, so you cannot avoid seeing some rounding artifacts when you squeeze 6 digits into a 4-digit DRO. My machine has 200 steps per mm (0.005 mm per step), so I never see that problem unless I would intentionally enter an oddball number into the DRO by hand.



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    Member CitizenOfDreams's Avatar
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    Default Re: Before I bin my whole control box...

    P. S. Some stepper drives have "decimal" microstepping options (1:5, 1:10, 1:20...). That would work nice for a "decimal" (5mm, 10mm...) ballscrew.



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    Community Moderator ger21's Avatar
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    Default Re: Before I bin my whole control box...

    It has to do with the specific steps/mm settings you are using. Mach3 will move to the nearest full step without exceeding the required travel distance. So, if one step > .002-.003mm, then Mach3 will stop just short of zero.

    This has no effect at all on accuracy, as Mach3 keeps track of position internally, and doesn't ever round off the position counter.

    Gerry

    UCCNC 2017 Screenset
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    Mach3 2010 Screenset
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    JointCAM - CNC Dovetails & Box Joints
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    (Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)


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    Default Re: Before I bin my whole control box...

    My machine has 0.023468669 resolution (42.62 steps/mm) and I edited my DROs to display only 2 decimal places, good enough for my needs.
    As I'm dealing with electronics all my life, my DMM has 4 decimal places, often I'm not observing rightmost 2 digits. That should be in accuracy and noise domain

    Make no mistake between my personality and my attitude.
    My personality is who I am. My attitude depends on who you are.


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    Default Re: Before I bin my whole control box...

    Thanks for all the feedback guys.
    I think Gerry's final comment has satisfied me
    "This has no effect at all on accuracy, as Mach3 keeps track of position internally, and doesn't ever round off the position counter."
    At the end of the day, Mach should put the spindle tip precisely where it should be. Even after "got to zero" DRO reads 1x step out, Mach still knows it's 1x step out and will run the next Gcode from true 0.000
    So I shall persist with current setup.
    Cheers!



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