Best lead screw - ball bearing mount system



  • that reminds me there was a video by alex kenis about this
    https://www.youtube.com/watch?v=2Z7mZVvPlc8



  • While I am trying to fix the squareness of the frame I finalized!the Z axis belt system
    This is what it came out.
    I tried to make the belt running as much as possible around the pulley with this setup all the pulley has 180 degree belt contact.
    The 2 tensioners are temporary , I am going to print a support for it
    Any suggestion will be appreciated.
    Thank you
    Andrea
    0_1559588633233_20190603_173238 (Medium).jpg



  • @claustro How come those front two lead screws are set so far back from the front of the frame?



  • @deckingman this is only a temporary disposition , at the end the 2 front lead screw will be as far as possible from the back one



  • @claustro said in Best lead screw - ball bearing mount system:

    @deckingman this is only a temporary disposition , at the end the 2 front lead screw will be as far as possible from the back one

    Ah OK. I was a bit concerned that the two side rails might flex due to the weight of the bed acting so far away from the end fixings. Those "Tee plates" might flex though. If you can, check for any deflection by using a dial gauge if you can lay your hands on one, and adding a weight to simulate the weight of the bed to the top of the lead screw couplings.



  • @deckingman

    I am trying to use your Z rail configuration with only 2 carriage in a diagonal disposition .
    If you talking about the plastic tee plate , the one that fix the 2020 that support the 2 front lead screws, I am going to switch to aluminum one as soon I 'll have my CNC running . ( it will be my first easy test with aluminum 🙂 )

    I have a dial gauge and I surely check what you suggest.

    0_1559593583822_Immagine.jpg



  • @claustro For info, here is how I mounted my lead screw blocks.

    0_1559597136362_ZAxisCompleteSmall.jpg

    So each block is supported on two 2020 extrusions. One might be OK but check for deflection.



  • I have 2 spare 2040 peaces I can always copy your design in case I'll find some flex



  • I changed the setup following your tips this is the result.
    Now I have to choose if make a bed leveled by lead screws or by another set of screws only for the bed.

    0_1560415418410_20190611_184108 (Small).jpg



  • @claustro That looks very familiar ☺



  • @deckingman eh eh 🙂



  • I am thinking to change my setup.
    with only one bearing when I tension the belt the shaft tend to be dragged towards the centre, creating tension on the lead screw, for this reason I am making another support for another ball bearing under the previous one fixed on the other side of the vslot. The 4cm distance between the 2 bearing should improve the stiffness of the system.



  • this is what I did
    0_1560792326047_20190617_191558 (Piccola).jpg



  • I have had issues with the z-axis due to that the 8mm hole on the pulleys are slightly oversized. Advertised 8mm, real world 8.07mm. And the lead screws tend to be slightly undersized, typically 7.9mm. This may lead to that the pulley is mounted at a slight angle causing massive z-banding. With an 8mm pitch screw it is not very visible, but with a 1.5mm pitch screw it certainly is.

    The nice screw @claustro has should solve that problem. Where did you find such a screw?
    My goto screw-peddler offers them with a machined 5mm end, I'm very tempted to get one of those.

    @sinned6915 said in Best lead screw - ball bearing mount system:

    Proper design would be to use a pair of angular contact bearings that bear on a shoulder, but those are $$$

    0_1560801837598_AngularBearing.jpg
    $5 a piece on ali, seems to be good quality. A bit scary with an open bearing.

    Edit: Typo



  • @bondus - what bearing is that? you have piqued my curiosity.
    looking at my printer now, i realize that i might have left out and important bit- i used a shaft collar on there too between the pulley and the thrust bearing-
    https://www.mcmaster.com/6655k54
    and i think
    https://www.mcmaster.com/6157k32



  • @sinned6915. Clamping shaft collar, should get a straighter clamp than with a set screw, I need to get some of those.

    The bearing is a 798C, 15 degree angle bearing. Mochu has their own shop on ali, lots of specialized bearings. I have bought many bearings from them, they are good.
    0_1560867899433_IMG_20190618_160007793_HDR - Copy.jpg



  • I got the best results with this solution (assuming that the Chinese friends inserting the axis exactly) 0_1560873439748_2019-06-18_18-54-56.png



  • yes the sfu1204 are working nicely on my printer as well.
    no play and very rid-git. you might even be able to use them without linear guides.



  • @bondus said in Best lead screw - ball bearing mount system:

    The nice screw @claustro has should solve that problem. Where did you find such a screw?

    I am not a native english speaker so maybe I am l misunderstanding something.
    My lead screw is a regular 2mm pitch Chinese lead screw and it is connected with a 8mm to 8 mm coupler with a 8mm shaft.
    I am having quite difficult aligning perfectly the lead screws but I think that it will not affect a lot the Z if the bed is correctly fixed in X and Y ( with V slot wheels in my case).

    I can't understand the shaft collar and 15 degree angle bearing. What would be the advantages over thrust bearing and regular ball bearing like I did?



  • @claustro said in Best lead screw - ball bearing mount system:

    I can't understand the shaft collar and 15 degree angle bearing. What would be the advantages over thrust bearing and regular ball bearing like I did?

    I realize now that your picture above shows the screw and shaft, without the coupler mounted.

    A shaft collar: 0_1561311157196_e173d6c3-8b04-4cbc-a76f-4198429aa4e8-image.png

    An angular bearing is very similar to a regular deep groove, but the surfaces the balls contact are at a slight angle. They can take axial load, in one direction, and radial load. They seem to be a specialist bearing only available with tight tolerances and a high price.
    0_1561311733290_1be53616-bf0f-472e-87c9-34c888daa2fc-image.png


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