Z axis Lead Screw

This topic contains 10 replies, has 5 voices, and was last updated by Profile photo of KRavEN KRavEN 7 months, 2 weeks ago.

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  • #11711
    Profile photo of Gannicus
    Gannicus
    Participant

    Any reason to not use a lead screw for the Z axis instead of the all thread?
    Can it be used? Using this only for CNC work, with a 3″ workable Z axis height.

    Not a fan of allthread for things like these, just wondering is the lead screw is compatible with the design, or if anyone created a upgraded part that needs to be printed to use the lead screw.

    #11713
    Profile photo of Jason
    Jason
    Participant

    Should be no issue, lead screw is probably the better choice. Just need to know your lead screws specs so you can accurately set your steps per mm.

    #11723
    Profile photo of vicious1
    vicious1
    Keymaster

    The only downside I see is the 3D printer cheap leadscrews have a soft brass nut that might wear very quickly with the weight of a big tool on it, and they have a lot of slop that might affect your z dimensions. This cheap screws are design with light 3d printer gantries on them and only loaded in the direction of gravity. A cnc can experience loads opposite of this and you could have z variances of 1mm or more depending on bit selection, wear on the nut, material being cut. Think about a downcut through plastic. This might actually push the tool up, were regular bits pull the tool down.

    I have not done the math on loss or gain of z axis torque either.

    #11758
    Profile photo of Gannicus
    Gannicus
    Participant

    I’ll stick with the all thread then. You’ve been playing with this design for long enough, and haven’t had any issues with the all thread setup.

    #13492
    Profile photo of KRavEN
    KRavEN
    Participant

    The only downside I see is the 3D printer cheap leadscrews have a soft brass nut that might wear very quickly with the weight of a big tool on it, and they have a lot of slop that might affect your z dimensions. This cheap screws are design with light 3d printer gantries on them and only loaded in the direction of gravity. A cnc can experience loads opposite of this and you could have z variances of 1mm or more depending on bit selection, wear on the nut, material being cut. Think about a downcut through plastic. This might actually push the tool up, were regular bits pull the tool down.

    I’m using this one on my prusa i3 http://www.ebay.com/itm/322101010139. The anti-backlash nut was much larger than any of the parts I found on thingiverse so I had to design my own but I’m pretty happy with them. 2mm per turn still gives me plenty of resolution.

    Does the anti-backlash feature resolve the slop or backlash problems you described? What would be a suitable alternative to the brass anti-backlash nut?

    #13495
    Profile photo of vicious1
    vicious1
    Keymaster

    That Should solve it, those are pretty nice. Now the question is will the brass actually wear down quickly or not. That would be pretty cool if they held up. That anti backlash puts a lot more surface area on the threads. That might work pretty well. Good find.

    #13503
    Profile photo of Paul
    Paul
    Participant

    It can work great on 3D printer but will not for milling or engraving. The spindle/Z axis assembly must be as solid as possible and the backlash should be compensated by software, not hardware. The load on spring on this nut is 4-8N – it will compress at a very little load and the end mill will flutter under different loads (cut depth, side load, RPM speed, feed rate etc.) and break easy.
    Just my 2c and a little bit of full size CNC machining experience.

    #13526
    Profile photo of KRavEN
    KRavEN
    Participant

    So we need a stiffer spring Paul? How is the preload set? I’ll work on designing a new C-Z-Lower part. Hopefully I have the clearance and can still utilize the bearing above the anti-backlash nut.

    #13530
    Profile photo of KRavEN
    KRavEN
    Participant

    Guess I need to mod the nutlock part, not the C-Z Lower

    #13532
    Profile photo of vicious1
    vicious1
    Keymaster

    Have you tried the recommended way yet? I’m not sure if all that will fit and I’m not sure if it will improve anything but z axis speed.

    #13539
    Profile photo of KRavEN
    KRavEN
    Participant

    I’m still printing but hopefully I’ll get it built soon. Have about half the parts done.

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