549,843 active members*
2,915 visitors online*
Register for free
Login
Results 1 to 20 of 20
  1. #1

    Join Date
    Dec 2021
    Posts
    9

    Question Best bearings for BK12 support

    Hello,

    I am building my first CNC and start recieving linear motion pieces from China.

    I have got one of my SFU1605 kit and I noticed that I have got nearly 0.1mm of axial backlash on the BK12 support.

    This is due to the bearings that are "of course" cheap chinese one simply branded as "6001Z".

    I'd like to replace them but I have a few interrogations about them :

    - Angular bearing seems to be the best for axial forces but only one SKF angular bearing is over 50$.. it would means 300$ for the 3 axis (BK12) which is way too much for my build. Have anyone already tried chinese BK12 mentionned with angular bearing in it ? They only cost 15$.. I am a bit suspicious..

    - If I want to replace them with tradiationnal bearing (but quality one), should I take normal one or C3 one ? Because as I understand it, C3 is for additionnal clearance for high speed running. So it sound better to take standard one without clearance but on another hand "C3" bearings often seems to be mentionned as an advantage in ball screw kit. I am a bit confuse here..

    Thank if someone can help me.

  2. #2
    Member
    Join Date
    Nov 2013
    Posts
    1540

    Re: Best bearings for BK12 support

    Hi,
    angular contact bearings are the way to go.

    If you get matched pairs, and you would ideally, then yes you will pay big bucks. If however you buy just bog-standard angular contact bearings
    the price falls to about the same price as your 6001's. Of course they won't be matched but the chances are if you buy a few more than are needed
    you'll be able to get pairs that match well enough.

    Craig

  3. #3

    Join Date
    Dec 2021
    Posts
    9

    Re: Best bearings for BK12 support

    Quote Originally Posted by joeavaerage View Post
    Hi,
    angular contact bearings are the way to go.

    If you get matched pairs, and you would ideally, then yes you will pay big bucks. If however you buy just bog-standard angular contact bearings
    the price falls to about the same price as your 6001's. Of course they won't be matched but the chances are if you buy a few more than are needed
    you'll be able to get pairs that match well enough.

    Craig
    Thank you for your reply Craig.

    I was aware that angular bearing have a direction of mounting, like face-to-face, back-to-back, .. But I didn't know they had matching pair.

    What do you mean ? They are specially machined in pair or something like that ? Thank you to light me up.

  4. #4
    Member
    Join Date
    Nov 2013
    Posts
    1540

    Re: Best bearings for BK12 support

    Hi,

    They are specially machined in pair or something like that ?
    That is correct. They come from the factory as a pair such that when they are placed either face to face OR back to back they have the right
    preload. This is achieved by the inner and outer races being ground in just the right manner to take up all the lash and just a little bit more called preload.

    You can buy a single 7204 P4 grade bearing, P4 is the highly concentric grade specifically for spindle use, and a premium grade for about $40. If you want a matched
    pair the you'll pay $300.

    Craig

  5. #5

    Join Date
    Dec 2021
    Posts
    9

    Re: Best bearings for BK12 support

    Quote Originally Posted by joeavaerage View Post
    Hi,



    That is correct. They come from the factory as a pair such that when they are placed either face to face OR back to back they have the right
    preload. This is achieved by the inner and outer races being ground in just the right manner to take up all the lash and just a little bit more called preload.

    You can buy a single 7204 P4 grade bearing, P4 is the highly concentric grade specifically for spindle use, and a premium grade for about $40. If you want a matched
    pair the you'll pay $300.

    Craig
    What about these :

    https://fr.aliexpress.com/item/32847...rch-mainSearch

    7001 / DF / P5 : 20$ the pair. It's pretty cheap.

    Probably not top notch but maybe a lot better than the cheap 6001 I have in my BK12.

  6. #6
    Member
    Join Date
    Nov 2013
    Posts
    1540

    Re: Best bearings for BK12 support

    Hi,
    yes they look suitable. Note they are P5 grade and so that makes them much cheaper than P4 grade to start with. You don't need P4 grade
    for a ballscrew, for a spindle yes, for a ballscrew, no.

    Note also that they are DT types. You can get DF types which are matched for face-to-face use, DB types which are matched for back-to-back use and then DT types
    which can be used either way. The important point is that they do genuinely appear to be matched, so you'll be fine.

    You are fitting these to rolled (C7) ballscrews so the highest precision is not warranted. If you were fitting to a C3 or even a C1 ground ballscrew that you'd
    find in a million dollar VMC then you'd be using matched ceramic P4's at $500 plus a pair!!!

    Craig

  7. #7
    Member
    Join Date
    Jan 2005
    Posts
    13253

    Re: Best bearings for BK12 support

    Quote Originally Posted by karnalta View Post
    Hello,

    I am building my first CNC and start recieving linear motion pieces from China.

    I have got one of my SFU1605 kit and I noticed that I have got nearly 0.1mm of axial backlash on the BK12 support.

    This is due to the bearings that are "of course" cheap chinese one simply branded as "6001Z".

    I'd like to replace them but I have a few interrogations about them :

    - Angular bearing seems to be the best for axial forces but only one SKF angular bearing is over 50$.. it would means 300$ for the 3 axis (BK12) which is way too much for my build. Have anyone already tried chinese BK12 mentionned with angular bearing in it ? They only cost 15$.. I am a bit suspicious..

    - If I want to replace them with tradiationnal bearing (but quality one), should I take normal one or C3 one ? Because as I understand it, C3 is for additionnal clearance for high speed running. So it sound better to take standard one without clearance but on another hand "C3" bearings often seems to be mentionned as an advantage in ball screw kit. I am a bit confuse here..

    Thank if someone can help me.
    Yes, they are just a deep grove radial bearing, which is not suitable for a Ballscrew fixed end, Angular Contact is your best choice for the same housing, these want to be 30-degree not the standard 15-degree, 30 degree is the minimum to use for Ballscrews fixed end, normal cnc machines use 60-degree.

    They can be matched pairs which makes it easier for installation, but any regular 30-degree angular contact Bearing can be used, you will just have to make a shim to create the preload needed

    If you can't find 30-degree AC Bearings your size and amount you want to spend, then the standard 15-degree would work with light loading
    Mactec54

  8. #8

    Join Date
    Dec 2021
    Posts
    9

    Re: Best bearings for BK12 support

    Quote Originally Posted by joeavaerage View Post
    Hi,
    yes they look suitable. Note they are P5 grade and so that makes them much cheaper than P4 grade to start with. You don't need P4 grade
    for a ballscrew, for a spindle yes, for a ballscrew, no.

    Note also that they are DT types. You can get DF types which are matched for face-to-face use, DB types which are matched for back-to-back use and then DT types
    which can be used either way. The important point is that they do genuinely appear to be matched, so you'll be fine.

    You are fitting these to rolled (C7) ballscrews so the highest precision is not warranted. If you were fitting to a C3 or even a C1 ground ballscrew that you'd
    find in a million dollar VMC then you'd be using matched ceramic P4's at $500 plus a pair!!!

    Craig
    Of course, all proportion must be kept. I am building a small desktop CNC to mill aluminium so I try to avoid 0.1mm of backlash but I am not trying to go down to 0.01.

  9. #9

    Join Date
    Dec 2021
    Posts
    9

    Re: Best bearings for BK12 support

    Look like in the size I want (12 / 28 / 8) they are always 15°. The bigger they becomes the bigger the angle (30° than 60°)

  10. #10
    Member
    Join Date
    Jan 2005
    Posts
    13253

    Re: Best bearings for BK12 support

    Quote Originally Posted by karnalta View Post
    Look like in the size I want (12 / 28 / 8) they are always 15°. The bigger they becomes the bigger the angle (30° than 60°)
    Yes, that is small, 12mm shaft size, there won't be a lot of loading, unless you crash, your machine must be quite small.
    Mactec54

  11. #11
    Member
    Join Date
    Nov 2013
    Posts
    1540

    Re: Best bearings for BK12 support

    Hi,
    I use 32mm THK BNFN double nut C5 ballscrews with FK25 supports. THK list 7205 P5 bearing pairs for the supports. They have a 250 contact angle.
    If its good enough for THK to specify them its good enough for me to use them.

    Craig

  12. #12
    Member
    Join Date
    Jan 2005
    Posts
    13253

    Re: Best bearings for BK12 support

    Quote Originally Posted by joeavaerage View Post
    Hi,
    I use 32mm THK BNFN double nut C5 ballscrews with FK25 supports. THK list 7205 P5 bearing pairs for the supports. They have a 250 contact angle.
    If its good enough for THK to specify them its good enough for me to use them.

    Craig
    (...) THK would only specify a Bearing by the information they were given. 25° is used for spindle Bearings also, so would only be light duty for a Ballscrew thrust Bearing. regular machining centers use 60°.
    Last edited by burs; 01-03-2022 at 11:13 AM. Reason: insult
    Mactec54

  13. #13

    Join Date
    Dec 2021
    Posts
    9

    Re: Best bearings for BK12 support

    Quote Originally Posted by mactec54 View Post
    Yes, that is small, 12mm shaft size, there won't be a lot of loading, unless you crash, your machine must be quite small.
    Yes it's a small desktop CNC (320x220 working table). Commercial one I see generally use 12mm thread with 16mm linear shaft. I used one size above for security (16mm thread with 20mm linear shaft).

    I think I have all informations I need about bearings (once again, budget is the master), I will give a try to cheap 15° bearing I have seen and see how it will work. My project has still long to go before milling the first piece

    Thank you.

  14. #14
    Member
    Join Date
    Jan 2005
    Posts
    13253

    Re: Best bearings for BK12 support

    Quote Originally Posted by joeavaerage View Post
    Hi matec,



    THK have been in business long enough for me to trust them, not you.

    Craig
    This has nothing to do with THK, 25° is not far off of 30° in terms of thrust loading, both are light duty, in terms of thrust Bearings.
    Mactec54

  15. #15
    Member
    Join Date
    Jan 2005
    Posts
    13253

    Re: Best bearings for BK12 support

    Quote Originally Posted by karnalta View Post
    Yes it's a small desktop CNC (320x220 working table). Commercial one I see generally use 12mm thread with 16mm linear shaft. I used one size above for security (16mm thread with 20mm linear shaft).

    I think I have all informations I need about bearings (once again, budget is the master), I will give a try to cheap 15° bearing I have seen and see how it will work. My project has still long to go before milling the first piece

    Thank you.
    Yes, they will work fine for what you are building, so if you use regular 15° AC Bearings, mount them face to face, this you will need to shim the inner race only, so just assemble and measure the backlash and then make a shim just .001" or .025mm thicker than the backlash, you may need a little more depending on how much thrust loading there is on the Screw.

    Make sure the outer Bearing race is clamped tight in the Bearing Housing, or this will give you a false shim thickness required (Backlash number)
    Mactec54

  16. #16
    Registered
    Join Date
    Jan 2018
    Posts
    1097

    Re: Best bearings for BK12 support

    I got my mill basically close as I could with basic parts.
    Then cut all my own bearing blocks. They don't need to be circular perfect as long as they are truly flat for mounting to machine.
    Once you get the preload right and ballscrews fitted the AC bearings are solid.
    I did this to fit larger AC bearings of 10mm thickness.
    Installed 2 single back to back in there and they made a massive difference.

  17. #17
    Member
    Join Date
    Jan 2005
    Posts
    13253

    Re: Best bearings for BK12 support

    Quote Originally Posted by dazp1976 View Post
    I got my mill basically close as I could with basic parts.
    Then cut all my own bearing blocks. They don't need to be circular perfect as long as they are truly flat for mounting to machine.
    Once you get the preload right and ballscrews fitted the AC bearings are solid.
    I did this to fit larger AC bearings of 10mm thickness.
    Installed 2 single back to back in there and they made a massive difference.
    Which way is best, for Ballscrew mounting, depends on the design of the housing and if spacers are used.

    Normally for Ballscrew fixed Bearing end, the AC Bearings are mounted DF Face-to-Face, they can of course be mounted DB Back-to-Back this just depends on what works better for your build, most manufacturers only show the Bearings being mounted DF Face-to-Face configuration for Ballscrew mounting.
    Mactec54

  18. #18

    Join Date
    Dec 2021
    Posts
    9

    Re: Best bearings for BK12 support

    Hello,

    I just leave a quick reply here to share my feedback.

    I received today my cheap chinese 7001 angular bearing (https://fr.aliexpress.com/item/32847...425a6c37Hb0PSN) and they didn't change anything

    I still have the exact same amount of backlash in the screw than with the originals bearings. I have ordered 0.1 mm washer shim and I will try to put one between the two bearings to see if it helps !

    If it's not, I will just follow the advices here and just go with them to later machine my own BK12 support with proper bearings.

  19. #19
    Member
    Join Date
    Jan 2005
    Posts
    13253

    Re: Best bearings for BK12 support

    Quote Originally Posted by karnalta View Post
    Hello,

    I just leave a quick reply here to share my feedback.

    I received today my cheap chinese 7001 angular bearing (https://fr.aliexpress.com/item/32847...425a6c37Hb0PSN) and they didn't change anything

    I still have the exact same amount of backlash in the screw than with the originals bearings. I have ordered 0.1 mm washer shim and I will try to put one between the two bearings to see if it helps !

    If it's not, I will just follow the advices here and just go with them to later machine my own BK12 support with proper bearings.
    Check the depth of the BK12 housing the the 2 Bearings and that the end plate is clamping the outer Bearing race together in the housing, this is somewhere else that the backlash can come from.
    Mactec54

  20. #20
    Registered
    Join Date
    Jan 2015
    Posts
    20

    Re: Best bearings for BK12 support

    If it's not too late for you, try dy-global on ebay:

    https://www.ebay.com.au/itm/201599233474

Similar Threads

  1. BK12 Ballscrew Support with 45X90 Sigma profile
    By gumush in forum DIY CNC Router Table Machines
    Replies: 0
    Last Post: 09-24-2013, 06:23 PM
  2. Replies: 0
    Last Post: 07-27-2013, 06:44 AM
  3. Ballscrew support with ABEC 7 bearings... worth it?
    By erikjgreen in forum Linear and Rotary Motion
    Replies: 6
    Last Post: 10-09-2011, 08:01 PM
  4. How to: Spindle support bearings for Rotozip?
    By Marmot_Militia in forum DIY CNC Router Table Machines
    Replies: 0
    Last Post: 09-04-2009, 04:19 PM
  5. slideway support rails + oilite bearings
    By colormecnc in forum Linear and Rotary Motion
    Replies: 2
    Last Post: 07-13-2007, 09:03 PM

Tags for this Thread

Posting Permissions

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