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  1. #1
    Hi, I've been almost exclusively 3d carving and sign making never noticed my sizes are out.

    I cut a simple hose adapter a few times now and every time it's out but exactly the same amount, tried 3 different tools to cut it, from 1/2" to 1/8" end mills.

    I'm out by ~1mm on 33mm hole, the holes are round and all 4 cuts are out by the same amount, tried it fast and super slow the same.

    1610 Chinese ballscrew's from alixpress, direct drive, AM882's, 70v PSU, motors barely get warm after an hour of 3d carving.

    DDCSV controller generated gcode in Fusion and vcarve same results.

    What can be causing it and how do I solve it?
    http://www.mycncuk.com/threads/10880...60cm-work-area My first CNC build WIP 120cm*80cm

    If you didn't buy it from China the company you bought it from did ;)

  2. #2
    Sounds like your "steps per unit" calculations have gone a bit wrong. Can you recheck, or post all relevant data here so someone else can check your working?

    The other way of doing it is starting with a good first guess - which you have - and then modifying the "steps per" based on the results of a calibration run. Personally, if my calculated value were out by more than a tiny amount then I reckon something's wrong - my calculation or a machine error. Slipping coupling, missing steps, or whatever. However, others take the more empirical approach. In short - keep tweaking until you get the right answer! Mach3 actually has a calibration capability built-in but don't know about your controller.

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  4. #3
    Quote Originally Posted by Neale View Post
    Sounds like your "steps per unit" calculations have gone a bit wrong. Can you recheck, or post all relevant data here so someone else can check your working?

    The other way of doing it is starting with a good first guess - which you have - and then modifying the "steps per" based on the results of a calibration run. Personally, if my calculated value were out by more than a tiny amount then I reckon something's wrong - my calculation or a machine error. Slipping coupling, missing steps, or whatever. However, others take the more empirical approach. In short - keep tweaking until you get the right answer! Mach3 actually has a calibration capability built-in but don't know about your controller.
    On the ddscv it's steps per mm

    I have 8 microsteps
    so 8*200/10 (1610's) for X&Y 160
    320 for Z (1605)

    Just double checked this is definitely what they are set to.

    AM882 has fault protection it should detect missing steps and estop and I swapped all the couplings for these style, I bought the chunkier ones.

    Click image for larger version. 

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    so they're rated twice the nm of the motors.

    2 4nm in the bottom and 3nm on the gantry, PSU is 70v and 1kva.

    Will try and cut 3 holes at 33mm, 66mm and 99mm see if the error scales perfectly I tried cutting from speed of 0.5m/min to 10m/min exactly the same results.

    Carved a lot of 3d stuff on this machine and that's machining for hours not seeing issues there or sign making never noticed the size was wrong until I tried to make an adapter and it didn't fit.

    Both X&Y are out by the same amount not sure about the Z.
    Last edited by Desertboy; 31-03-2020 at 06:30 PM.
    http://www.mycncuk.com/threads/10880...60cm-work-area My first CNC build WIP 120cm*80cm

    If you didn't buy it from China the company you bought it from did ;)

  5. #4
    Sounds good to me. I'll step back and wait for the experts to comment!

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  7. #5
    I measured all 4 parts with calipers within 0.05mm of each other but just not the right size.
    http://www.mycncuk.com/threads/10880...60cm-work-area My first CNC build WIP 120cm*80cm

    If you didn't buy it from China the company you bought it from did ;)

  8. #6
    Quote Originally Posted by Desertboy View Post
    On the ddscv it's steps per mm

    I have 8 microsteps
    so 8*200/10 (1610's) for X&Y 160
    320 for Z (1605)

    Just double checked this is definitely what they are set to.

    AM882 has fault protection it should detect missing steps and estop and I swapped all the couplings for these style, I bought the chunkier ones.

    Click image for larger version. 

Name:	external-content.duckduckgo.com.jpg 
Views:	16 
Size:	55.4 KB 
ID:	27689

    so they're rated twice the nm of the motors.

    2 4nm in the bottom and 3nm on the gantry, PSU is 70v and 1kva.

    Will try and cut 3 holes at 33mm, 66mm and 99mm see if the error scales perfectly I tried cutting from speed of 0.5m/min to 10m/min exactly the same results.

    Carved a lot of 3d stuff on this machine and that's machining for hours not seeing issues there or sign making never noticed the size was wrong until I tried to make an adapter and it didn't fit.

    Both X&Y are out by the same amount not sure about the Z.
    The numbers are really only to get you in the ball park. There's always a slight error on the screws.
    Mine is similar on circles. I end up about 0.1mm too small so I just tweek my drawings to suit the machine. I add 0.1mm to inner circles such as do a 32mm as a 32.1mm.
    Then outer edges I add 0.05mm on each end (or I can set my stock to leave 0.05mm instead).

    This will give you a rough idea on methods of how to increase accuracy using Mach calibration. Or at least to check how close your machine is to see if that is the problem.
    https://www.youtube.com/watch?v=XkO5tc-jSxw
    Last edited by dazp1976; 31-03-2020 at 10:17 PM.

  9. #7
    JAZZCNC's Avatar
    Lives in wakefield, United Kingdom. Last Activity: 13 Hours Ago Forum Superstar, has done so much to help others, they deserve a medal. Has been a member for 8-9 years. Has a total post count of 7,267. Received thanks 1,239 times, giving thanks to others 80 times.
    Quote Originally Posted by Desertboy View Post
    AM882 has fault protection it should detect missing steps and estop and I swapped all the couplings for these style, I bought the chunkier ones.
    AM882 doesn't detect missing steps it's got stall detection which is a different thing altogether. It also only works above 300Rpm.

    Regards the wrong size parts then if the steps per is correct and you don't have slippage etc then I would be looking to the CAM and the tool offsets.
    Does the controller have tool offsets.?

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  11. #8
    What should the rising edge be set to?

    Click image for larger version. 

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    I have it set to uprising at moment
    http://www.mycncuk.com/threads/10880...60cm-work-area My first CNC build WIP 120cm*80cm

    If you didn't buy it from China the company you bought it from did ;)

  12. #9
    JAZZCNC's Avatar
    Lives in wakefield, United Kingdom. Last Activity: 13 Hours Ago Forum Superstar, has done so much to help others, they deserve a medal. Has been a member for 8-9 years. Has a total post count of 7,267. Received thanks 1,239 times, giving thanks to others 80 times.
    Quote Originally Posted by Desertboy View Post
    What should the rising edge be set to?

    Click image for larger version. 

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    I have it set to uprising at moment
    It depends on the controller and whether it looks at the rising or falling edge.

    However it's easy to test. Just write some G-code that moves back n forth few hundred short moves, say 10mm, then back to zero. If you have the wrong edge set it will lose a step for every direction change and it won't return to zero. Do this for each axis separately.

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  14. #10
    Quote Originally Posted by JAZZCNC View Post
    It depends on the controller and whether it looks at the rising or falling edge.

    However it's easy to test. Just write some G-code that moves back n forth few hundred short moves, say 10mm, then back to zero. If you have the wrong edge set it will lose a step for every direction change and it won't return to zero. Do this for each axis separately.
    OK I drilled a small hole just outside my normal machining area set that as X&Y 0

    then created code to
    G01 X10
    G01 X0

    1000 times doesn't seem to have shifted

    just running the Y code now

    Will try Z after that.

    Can I do something similar to see if I'm losing steps?

    Or is there some test code for that?

    In the manual there's "Level of Axis pulse signal" what does this mean? Is that the rising/falling edge?
    Click image for larger version. 

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    Last edited by Desertboy; 01-04-2020 at 03:46 PM.
    http://www.mycncuk.com/threads/10880...60cm-work-area My first CNC build WIP 120cm*80cm

    If you didn't buy it from China the company you bought it from did ;)

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