584,800 active members*
4,687 visitors online*
Register for free
Login
Results 1 to 14 of 14
  1. #1
    Join Date
    Nov 2005
    Posts
    24

    Bearings for screw drives

    I'm building a CNC machine and will be using large diameter ballscrews for vertical and horizontal movements, what types of bearings at each end of the shafts should be used to get the best performance? Roller? Thrust? combinations?

    Also, any tips on designing high-quality shaft end seats/mounts for these bearings.

    Any help is greatly appreciated.

    Thanks!

    Larry

  2. #2
    Join Date
    Nov 2005
    Posts
    938

    screw bearings

    I asked a similar question in another thread recently.

    Most of the people I have seen make their own bearings using a skate bearing (or something similar) seated in a MDF or HDPE housing. These are usually trapped by nuts to hold the lead screw in place (see thread by joe2000che regarding his 2007 machine for pictures).

    I was asking about the use of flange bearings:

    Has anyone tried using flange bearings (similar to pillow blocks) http://www.wttool.com/c/40410009p to anchor the leadscrews, or are they to stiff? I've used then in a number of aplications (non-cnc stuff like polishing wheels and customized sanding wheels) and they seem to be pretty good. They may be a bit stiffer and heavier than the home made things with the skate bearings. But they also have the locking allen screws to trap the leadscrew tightly and may decrease the whipping problem.
    This seemed to have met with at least one aproval.

    Steven

  3. #3
    Join Date
    Aug 2004
    Posts
    2849
    Check out misumiusa.com. I'm using a single bearing 6001ZZ (U-BASA 6001ZZ) on the un-driven end and a dual bearing setup on the driven end (u-BASB6001ZZ)...my idea is to preload the driven end. Also they are having a 50% discount until Feb 2006, so the parts are great deals.

  4. #4
    Join Date
    Dec 2005
    Posts
    13
    Go to 5 bears website, he explaines the type of bearings & details on mounting.

  5. #5
    Join Date
    Dec 2005
    Posts
    13

    Leadscrew bearings

    Go to the 5 bears website. He explaines how to mount the right kind of bearings beatifully.

  6. #6
    Join Date
    Nov 2005
    Posts
    24
    Thanks to each of you for your help. I will do a little more research using the information you have provided.

    Billyum, do you know the url for 5 bears website?

  7. #7
    Join Date
    Mar 2003
    Posts
    35538
    Gerry

    UCCNC 2017 Screenset
    http://www.thecncwoodworker.com/2017.html

    Mach3 2010 Screenset
    http://www.thecncwoodworker.com/2010.html

    JointCAM - CNC Dovetails & Box Joints
    http://www.g-forcecnc.com/jointcam.html

    (Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)

  8. #8
    Join Date
    Nov 2005
    Posts
    24
    I've just looked over the 5bears site not only is it informative it uses great photography, has excellent step by step continuity and the writing is clear and concise. An A+ without hesistation. I'm headiing back for more!

    Thanks again for the direction.

  9. #9
    Join Date
    Jul 2003
    Posts
    167
    another thread I liked, that shows how to make some bearing supports if you have the tools to do it
    http://www.cnczone.com/forums/showthread.php?t=13881

    vipertx, how does one get the 50% discount at misumi?

  10. #10
    Join Date
    Dec 2005
    Posts
    8
    I am working with my local bearing store, who recommended a sealed bearing flange mounted. I have installed them, but was a little reticent due to the resistance. I can turn the shaft by hand and move the z axis carriage along the y axis. I intentionally oversized my stepper for that reason. The bearing store said that if I did not seal whatever bearing I used, that I would have trouble. Frankly, I am still worried about the resistance. Has anyone tried sealed bearings, and did it overheat the stepper? If I had the tools, I would fabricate like 5bears. If anyone has a source, let me know and I will see if I can afford.

  11. #11
    Join Date
    Nov 2005
    Posts
    24
    Hello again,

    You may be interested in a request for information I posted in the Bridgeport Mill forum regarding bearing selection and block designs for the Brigdeport type ballscrews I am using in my design.

    Jimbo, I just looked over the thread you suggested, thanks!

  12. #12
    Join Date
    Dec 2005
    Posts
    3319
    How accurate and how repeatable do you want to get and how much do you want to spend???

    An ABEC 7 true ball screw bearing (IE 24TAC47...) will be deadly accurate, have minimal axial runout and be very stiff due to precise and high preloading and inherent stiffness (IE; 60 deg internal contact angle). It will spin as smooth as glass and last a long time.

    A deep groove ball bearing (IE 6204 shimmed to preload) will not be as stiff as the above, be MUCh cheaper and spin like a cement mixer at a fraction of the preload of the 24TAC47. It will last OK but not as long as the above TAC at the same preload is a 6204 is designed to be loaded at high axial loads as a true ball screw bearing

    Check out the prices for a pair of NSK 6204's (or anybody's) and then check the price (and accuracy specs) of 24TAC47( ) ball screw bearings or anybody's equivalent. ( ) denotes more data but can't recall it off hand.

    Simply put, you get what you pay for.

  13. #13
    Join Date
    Nov 2005
    Posts
    24
    Thanks for the reply.

    I've been pondering the price question and really would love to get the abec 5 or 7 quality ground angle contact bearings (at a luncheonette price . I've got a pair of NDH 7305 angular contact bearings I'll try before committing to a higher cost option. The design of the End #1 block is still in flux.

    Do you have any thoughts on bearing End #1 block design, (covering 73mm of 25mm bare shaft using these two bearings), are two bearings in this proposed configuration sufficient?

    Regards,

    Larry

  14. #14
    Join Date
    Dec 2005
    Posts
    3319
    Maybe so and maybe not....

    "Bearing suffiency" is ultimately a function of speed and load. Most bearing manufacturers engineering handbooks outline the procedure for calculating life for angular contact bearings.

    You MUST have radial and axial loads and appropriate speed assumptions for the calculations to mean anything. Unltil and unless you (or someone) do/does the load/life calculations, the "sufficiency" of any bearing being applied is purely a guess.

    Yes, you and every machine tool bearing user would love to get luncheonette bearing prices for ABEC 5 or 7 bearings but that rarely happens.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •