Z-Axis either not rising as much as it should, or going down farther

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This topic contains 9 replies, has 3 voices, and was last updated by  Ryan 9 months, 3 weeks ago.

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  • #53365

    Andrew
    Participant

    So this issue I’m having is a little hard to describe.  First, I can do 2d cuts no problem, it’s 2.5d that are the issue, and I’m using fusion 360 with the v10 post proccessor.

    The issue I’m having is, initially it raises the spindle to z15, does a move to the starting position, then lowers to z0 and starts to plunge to being the carve.  This seems to work perfectly as expected.

    After about an hour of carving, when it’s supposed to be cutting at 2mm into the stock, it’s really cutting much deeper (somehwere around 3-4mm).. even though on the controller still thinks it’s at 2mm. After about another half an hour, the Z is so much offset from where the controller thinks it is,  that the retract move doesn’t move the tool above the stock and it winds up crashing into wood and getting stuck.

    I have no idea if this is a hardware issue, or a software issue, or where I would even begin to start troubleshooting.  Any advice for you guys would be greatly appreciated!

    Thanks in advance!!

    #53366

    Ryan
    Keymaster

    What speeds are you using form your Z axis rapids, plunges? Are you using a T8 or a 5/16 allthread? What control board, what drivers, what current are they set to , step rate, what steppers? What tool are you using for a spindle, What is your build’s max Z axis length?

    1 user thanked author for this post.
    #53374

    Andrew
    Participant

    What speeds are you using form your Z axis rapids, plunges? Are you using a T8 or a 5/16 allthread? What control board, what drivers, what current are they set to , step rate, what steppers? What tool are you using for a spindle, What is your build’s max Z axis length?

    Thanks for helping!!

    In the post processor, I have high speed z feed rate to 400, plunges are 250 mm/min and a 5/16 rod. I bought the parts kit from here in 2016.  It’s running on an arduino mega with ramps running DRV-8825 drivers.  I have them set to 0.9.   Steppers are nema 17s that came with the kit, for step rate I flashed the default marlin from here which has steps per unit set to 4535.44

    For the spindle I’m using a dewalt dw660, and max z travel is about 3 inches but at the moment I’m only trying to carve into a 3/4 in piece of wood.

    Let me know if you need anything else!

     

    EDIT:

    Steppers are DRV-8825 at 0.9

    #53383

    Andrew
    Participant

     

    #53384

    Ryan
    Keymaster

    Okay. The problem is probably the screw itself. Plenty of lube? Does it move really really easily all the way up and down with your fingers? If not any slight bump can make it no work so well. It can be an alignment things as well where the screw is slightly angled so the entire time it drags.

    The other things are 0.9V on the DRV8825 is a lot, like right at the edge of what they can sustain with a fan directly on them, and the stepper is probably actually getting really hot as well. This should not be the problem but it could be.The lower z mount should also be supporting the coupler a bit.

    1 user thanked author for this post.
    #53385

    Andrew
    Participant

    zero lube on the lead screw… I didn’t even know that was needed, so maybe that’s the issue.. it turns with my fingers but not super easily.. needs a solid 6/10 on the finger force scale.

    What kind of lube should I get?

    Also I lowered the vref on the z stepper to 0.66 and it started making that noise every 5 seconds (video below).  Is that because I don’t have lube?

    #53386

    Andrew
    Participant

    #53392

    Barry
    Participant

    I use white lithium grease.  I’ve heard spray graphite(dry lube) works as well.  If you go the graphite road, cover everything before you spray it.  It can stain damn near anything.

    1 user thanked author for this post.
    #53394

    Andrew
    Participant

    @barry and @ryan thank you guys so much for your help!  I put lithium grease on the threads and spent 4 minutes moving it up and down randomly, no stepper noises and at the end, Z0 returned exactly to the stock top as it should.  Hurray!

    Trying a 2.5d cut now… thank you guys so much!

    #53398

    Ryan
    Keymaster

    Bump your driver up to 0.7 or 0.75 just in case.

    Glad to hear a little lube is all you needed. Easy fix!

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