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Travel distance accuracy off by 1% in Ox Metal build. >Problem solved<

Discussion in 'CNC Mills/Routers' started by NoX, Jan 22, 2017.

  1. NoX

    NoX Well-Known
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    Hello,

    Because this being my first post on this forum... my name is Gerard. I'm from the Netherlands and recently build my own CNC router, the Ox Metal (see picture below). After solving most of my encountered problems myself (so far) during this build, I'm now out of options to solve this one on my own.

    I have an issue/problem with the accuracy of my machine being off by approximately 1%. As stated earlier I recently build the Ox-Metal using the CNC-Xpro V3 controller with 4 Nema23 steppermotors and 8mm ACME leadscrews.

    Yesterday I wanted to do a job on the Ox. The material I worked on was a X-400mm x Y-600mm x Z-22mm MDF. Home position was bottom left.

    1. Before I click the send button, I always manually send the bit to all 4 corners of the material first to make sure there are no X Y traveling problems. So, I zero the machine on the bottom left and then send the machine X-400mm. Although Universal Gcode Sender says 400mm, the actual distance is 404mm. Same thing for the Y. When I manually send it to Y-600, it stops at 606mm. This doesn't change after sending it back and forth multiple times. So the measurement is steady.. it's just off by 1%. For every 100mm, the machine adds 1mm. Tried almost everything to fix this or find the cause of it. No luck so far.
    1. Soft reset X-Pro V3
    2. Restarted the laptop
    3. Hard reset on the X-Pro board
    4. $RST=# : Erases and zeros all G54-G59 work coordinate offsets and G28/30 positions stored in EEPROM.
    5. $RST=$ : Erases and restores the $$ Grbl settings back to defaults.
    6. Tried using UGS nightly build 2.0
    7. Tried using GRBL panel...
    Still no luck. Even right after $RST=$ command, with (almost) no settings changed, the problem persisted.

    My GRBL settings are;
    $0=10 (step pulse, usec)
    $1=25 (step idle delay, msec)
    $2=0 (step port invert mask:00000000)
    $3=2 (dir port invert mask:00000010)
    $4=0 (step enable invert, bool)
    $5=0 (limit pins invert, bool)
    $6=0 (probe pin invert, bool)
    $10=3 (status report mask:00000011)
    $11=0.010 (junction deviation, mm)
    $12=0.002 (arc tolerance, mm)
    $13=0 (report inches, bool)
    $20=1 (soft limits, bool)
    $21=1 (hard limits, bool)
    $22=1 (homing cycle, bool)
    $23=3 (homing dir invert mask:00000011)
    $24=25.000 (homing feed, mm/min)
    $25=1000.000 (homing seek, mm/min)
    $26=250 (homing debounce, msec)
    $27=5.000 (homing pull-off, mm)
    $100=200.000 (x, step/mm)
    $101=200.000 (y, step/mm)
    $102=200.000 (z, step/mm)
    $110=2500.000 (x max rate, mm/min)
    $111=2500.000 (y max rate, mm/min)
    $112=1500.000 (z max rate, mm/min)
    $120=20.000 (x accel, mm/sec^2)
    $121=20.000 (y accel, mm/sec^2)
    $122=20.000 (z accel, mm/sec^2)
    $130=595.000 (x max travel, mm)
    $131=750.000 (y max travel, mm)
    $132=52.000 (z max travel, mm)

    I don't know what else there is to try anymore. All my GRBL settings involving steps ($100, $101, $102) are correct. The only thing I can think of at this point is that something goes wrong inside the X-Pro. Few days ago, during another cut, the machine took a BAD wrong turn whilst milling a 580mm diameter circle.

    [​IMG]

    After about 75% of the second pass it ran straight across the table and crashed beyond software limit and ignoring the hardware limit. Had to pull the plug from the 24V PSU. After all was reset, I run the same file over and over again to reproduce the issue... no problem whatsoever.

    What else is there to try and fix this accuracy issue? Can someone please help me out?

    TIA
     
    #1 NoX, Jan 22, 2017
    Last edited: Jan 22, 2017
  2. Darathy

    Darathy Journeyman
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    1. It might be that the drivers are overheating and losing stepps,do you have a fan runing over the Xpro?

    2. Did you measure when you built the Ox how far it actualy travels when you send it in any direction eg:100mm and it actualy travels 100mm? or did you just put the settings from instructions? I have found that my plate maker didnt have the correct settings from the start(the ones that were reported from Video asembly) i guess each machine has diferent due to tolerances of parts.
    If 1.didnt help i suggest you try adjusting the settings $100,101,102 and heres something to help: RepRapCalculator

    Hope you fix your problem :)
     
  3. NoX

    NoX Well-Known
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    That was spot on!! THANKS

    Yes I have 2 fans blowing, one in and one out, right above those drivers.
    IMG_5620.JPG


    But what I didn't do (and should have done obviously :banghead:) was calibrate the machine the way you described.

    The first job was a small drawing of the Aztec Sunstone.
    IMG_5534.JPG

    Because this looked oké, I thought my (factory default?!) settings were correct. The 1% mismatch in both directions is not noticeable at all.

    The second job was calculated from center point and I just checked if the machine stayed within the boundaries of the material. So, didn't think/see something was off at that point.

    The last job (still needs to be cut luckily) showed me that there was this accuracy issue. I totally trusted and copied the '200 steps per revolution' settings from the instructional video's because their based on calculations. Find it strange that all my 4 Nemas have (or should I say had) this issue and nobody else encounters/needs this adjustment (or didn't mention/calibrated).

    My original settings
    $100=200.000 (x, step/mm)
    $101=200.000 (y, step/mm)
    $102=200.000 (z, step/mm)

    My new settings
    $100=198.020 (x, step/mm)
    $101=198.020 (y, step/mm)
    $102=198.020 (z, step/mm)

    Problem solved (mystery created ;-))

    Thanks again for your help. You saved my day!! Thought this was gonna take quite some time... luckily it didn't.

    LETS DO SOME CUTTING... FINALLY ;)
     
    Nunoz likes this.
  4. Darathy

    Darathy Journeyman
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    You are welcome ,glad it helped :)
     
  5. Rick 2.0

    Rick 2.0 OpenBuilds Team
    Staff Member Moderator Builder

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    You'll find the error is in the screws not the motors. The motors are doing what they are supposed to do. The screws were just rolled 1% too long.
     
  6. NoX

    NoX Well-Known
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    Just made a cut... all looks good. Only thing is now that, when I zero the machine, it doesn't go to 0,000 but to 0,001 or 0,002. Not exactly 0,000. Not that it's a big problem... it's just my autism that wants to see 0,000.

    It doesn't even move when putting in those small numbers. Don't know if it did before.

    @Rick 2.0 seems like I have some screwed up screws then. Didn't expect that such a product has so much deviation. Ahh well... life goes on.

    Thanks!!
     

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