Z Axis constrained or not constrained?



  • Quick question my z axis screws wobble a little so I was wanting to buy a couple of new ones.
    While doing some reading a the subject I came across someone saying to leave the z Axis leadscrew unconstrained on the top.
    Now my question is which is better? I tried to constraine mine but the wobble would almost bind the up.

    So what are yout setups . Thanks


  • administrators

    Z screws should not be constrained at the the top. If you constrain them then any wobble will be transferred to the axis supported on Z and thus to the print. In extreme cases they can bind.



  • Depends on how fast you want to drive the system. If you go slow it can be open. Your Z is going slow.

    //P



  • The Z axis should be constrained from any side to side movement by using linear guides. Screws should only provide lift and therefore be unconstrained. If the Z axis has wobble, then you need to look at the linear guides, not the (lifting) screws.



  • I'm using four 12mm linear rods so i don't think thats the problem, its the screw that when it turns it will wobble a little.
    You can see it if you roll it on a flat surface thats its not perfect. I doubt that it can effect the table in a sidewards motion, vertical maybe.
    I do go slow on the Z axis have no reason to have to go to the bottom in 5 seconds. šŸ™‚



  • My example is inverted but with my new leadscrew delta the leadscrews are constrained at the bottom, the motors are at the top with flex couplers on them and they are attached to linear rails. It would be nice to attach them in such a way that they have no lateral constraint only vertical but I have not come up with a way to do this reliably and it prints fairly well.



  • @Synapsis:

    I'm using four 12mm linear rods so i don't think thats the problem, its the screw that when it turns it will wobble a little.
    ā€¦..................

    In that case it just means that your screws are not perfectly concentric which isn't a problem as long as you don't constrain them. The fact that they are slightly eccentric won't cause a problem - you'll still get the desired linear movement for a given rotational movement. Personally, I'd leave them alone but if you insist on replacing them, don't constrain them but leave them floating as much as possible. Otherwise, any eccentricity or misalignment will apply sideways forces which may cause the binding of the guides.



  • Thanks Ian for the suggestion after what you said I will at this point leave them as they are.
    Of that little wooble like you say isn't a problem no need to change if it works.

    Thanks to all for the info.


 

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