Remounting my print bed

  • Hello all,

    I'm looking for a bit of advice. I am having a difficult time keeping my bed level. It's a 500x500mm 3/8" tooling plate using a variation of a kinematic mount. I think part of the issue is that I was not able to get the surfaces that the ball headed bolts interface with smooth enough, and I haven't been able to find a machine shop that is interested in doing the work. As a result I am considering a fixed mounting for the print bed to its frame adding a third Z motor. Once I've done that I am hoping that between three point automatic bed leveling and mesh bed compensation I should be OK. I am not sure what the specs for the current Z motors are beyond being NEMA 17 60mm so I am thinking about replacing the two existing motors when I add the third Z motor so they are all the same NEMA 17, 2.1a, 4-lead 60mm motors. I am thinking that I will replace the two existing 12mm linear rods with the 8mm lead screws. Should I put one of the 12mm linear rods between the lead screws for support or would that potentially cause binding? My printer is based on a TronXY X5S-500. I am open to any advice, I have done everything I can think of to stiffen the frame of the printer with no apparent change and am running low on ideas, any insights will be appreciated. I've attached a picture for clarity... maybe...


  • The heavy bed assembly is being supported by 3 small diameter lead screws. That will tend to cause the screws to bow which will in turn cause some lateral shifting of the bed as they rotate. I think it would be better to hang the bed from the screws and put the motors at the top of the Z axis.

    Long, thin, end-supported guide rails will tend to flex if there's any lateral force on them (from bowed lead screws), allowing the bed to shift, which will show up in prints as poor Z axis quality. It would be better to use fully supported rails that will be less likely to flex. That would require adding more t-slot or some rigid panels to the frame.

    If you can't get a decent smooth slot cut in the bed you can screw on a piece of metal that will serve the same purpose. A piece of U channel stock or even two separate pieces of metal arranged so they are parallel can replace a milled slot.

  • First of all, those linear rods are way too small for that length. I would suggest running at least 20mm rods for that distance to get acceptable stiffness.
    if you dont want to do that, i would suggest moving the rods maybe 50mm closer to the lead screw in the center, this will cause the bed to rock less along the axis of the two leadscrews.

    Another possibility is to leave the rods there and buy another leadscrew + motor and mount them right next to the linear rods. this will also reduce the flexing of that bar where the current leadscrew is installed in.

    How flexible is that bar anyway? it looks like the heavy bed could easily get that bar to flex

    And i agree with Mark, the leadscrews would be better off hanging. However, they should really be mounted on a fixed side, screwed into an axial ball bearing which can take the axial load.
    It has been a thorne in my eye for quite a while already that these cheap chinese kits use the stepper motor (sometimes even with a flexible coupler) as an axial bearing. If you press a little too hard on the shaft, it pops out.
    The motors would be OK at the bottom if the leadscrews would be rigidly mounted at the top.

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