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Pocketing coming out wrong.

Discussion in 'CNC Mills/Routers' started by Jake Borg, Oct 10, 2020.

  1. Jake Borg

    Jake Borg New
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    What could be the cause of this it was supposed to pocket 9mm inside the letters, some parts of the letters came less while the other parts came more than 9mm I ran the job twice to see if the motor skipped or anything but it goes over the same path exactly. Using blackbox for controller with open builds cam software trough the browser. Attached gcode
     

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  2. JustinTime

    JustinTime Veteran
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    That looks like backlash. Check that you don't have a loose belt, if that's what you use or a loose pulley (screw not tight). Search this forum for backlash.
     
  3. Jake Borg

    Jake Borg New
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    Wouldn't the backlash be random if that was the case? I ran the cut twice from same zero position and it cut in the same position over again.
     
  4. Rob Taylor

    Rob Taylor Master
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    No, backlash would be pretty consistent under the same cutting conditions- that's why on controllers more advanced than grbl you can actually compensate it out in software. If this was the same toolpath on the same part that was still on the machine after the first cut, you may not have seen the same level of deflection under load/tool pressure, but it would have stayed within the same channels, most likely.

    If this is what it produces with a good CAD/CAM setup, there's a pretty high chance the machine needs to be drastically tightened up.
     
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  5. Alex Chambers

    Alex Chambers Master
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    Loose drive pulley found so far.
    Alex.
     
  6. Jake Borg

    Jake Borg New
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    went and got lock right will let you guys know tomorrow when I take the machine apart to tighten everything
     
  7. Jake Borg

    Jake Borg New
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    No luck, slight improvement but still getting a mm or two on certains pocket paths off. Tightened everything. :( Could it be the fact that it is a belt driven system I will be having these kind of pockets?
     
  8. JustinTime

    JustinTime Veteran
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    When you say 'Tightened everything' do you also mean the belt itself? It should be tight like a guitar string with very little sag when you push on it.
     
  9. Jake Borg

    Jake Borg New
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    Yes i believe i tightened as much as i could, I even added longer bolts and a lock nut to be able to tighten it easier as the current system with the ball screw was not cutting it. I know have a problem when moving the y axis with the motors that the belt is sliding out of the side and having to re attach the hole thing. The pulley on the motor is in line with the wheels. Ive decided to purchase lead screws and waiting for them to arrive as I believe the belt system is just too inferior for the 1510. Seems like ooznest scrapped selling them too possibly for the unreasonable backlash they cause. The belts seem too small for this kind of build and no easy way of adding dual or a thicker belt.
     
  10. Peter Van Der Walt

    Peter Van Der Walt OpenBuilds Team
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    While leadscrews are better, your results are also not typical of belts either - somethings is still loose (if it hasnt improved from the pictures above)
    Many 1510s out there running fine (with about 12kg of pull on the GT3 6mm Belt, it works)

    Its just a matter of finding what is loose on yours (you could end up replacing the drive system, and whatever was loose, still is, then you have the same problem even with leadscrews)

    - With machine off, grab endmill and give it a wiggle, see what gives and moves when it shouldn't
    - using your hands (more sensitive to movement than eyes) follow the wiggle until you find what along the way is allowing movement, then address that
    - Popular things include wheels improperly adjusted (some tiny bit preload needed), pulleys loose on motor shafts (drop of locktite, setscrews positioned on flat of D-shape motor shaft, tightened well), spindle mount loose, shaft coupler on leadscrews slipping (loose setscrews, locktite), bad workholding (stock moving, even if machine is rigid)
     
  11. Jake Borg

    Jake Borg New
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    I had found things loose and re tightened everything, I still got around 1mm of cutting defect. Could not find anything else loose. If I could get it .5mm better with leadscrews I will be more than happy. I think i may have not tightened the belts good enough but from what i read the leadscrews are significantly better and if i get the cuts slightly better il call it a win win :)

    I forgot to mention there was a good imrovement and its around 1mm off now. But belts kept slipping out of the pulley for me for some reason, I think i may have tightened them too much.
     
  12. Peter Van Der Walt

    Peter Van Der Walt OpenBuilds Team
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    What do you men by that? Slipping on the teeth, or literally falling of the side?


    They need to be guitar string tight. You can overtighten but you need a 200lb gorilla hanging on it - to break the glass fiber reinforcement inside


    Refer to the science, not the rumours (;
    On a machine that big, frame deflection can be 1mm How to calculate V-Slot® deflection with an aggressive cut recipe (feed and speed) so don't put all the blame on Belts (as I mention above, you might replace with leadscrews on that assumption without finding the root cause, and then be out of pocket for nothing

    Do the belts go loose after a job (ie did you remember the cable tie to hold the belt in the tensioner, and is the teeth meshed together)

    What machine is it (don't see above a mention sorry if I missed it)
     
  13. Jake Borg

    Jake Borg New
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    yes I added the cable ties it's a 1510 workbee what could be the reason of the y axis belts slipping out of the pulley ?
     
  14. Peter Van Der Walt

    Peter Van Der Walt OpenBuilds Team
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    What do you mean by that? Include Pictures.

    See my question earlier

    Include photos of the issues, belt attachments, tensioners, pulleys, etc so we can check your machine for you. Without pictures its harder
     
  15. Jake Borg

    Jake Borg New
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    Will get them for you tomorrow morning thank you. I meant the belt slipped 3 times out of the pulley and out of the small black wheel into the C Beam
     
  16. Peter Van Der Walt

    Peter Van Der Walt OpenBuilds Team
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    Sounds like something around those parts assembled wrong, or the belt being very loose
     
  17. Jake Borg

    Jake Borg New
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    Ive noticed the machine wobbles from corner to corner as the table underneath that the machine sits on was not flat. The mdf sheet slagged slightly on the edges of the table thus not keeping it flat or level. I will be working my way from the table to the machine and installing lead screws along the way to try re do the build in a more concentrated way. Im hoping il get it right this time.
     

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