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  1. #1
    Join Date
    Feb 2009
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    1290

    Bearing Blocks.

    A question on bearing blocks.
    I'm using the bearing block pictured below.

    My lead screws ends are machined to fit the bearing block like the screw below.


    The question, do you think the inner race of the bearing should be supported on the back side of the bearing block?

    Thanks

  2. #2
    Join Date
    Jul 2007
    Posts
    177
    I guess you need that block for loose side bearing !

    Think about the following your spindle is hanging through a bit due to the own mass.... so the end in bent upwards someway .. now turn this one and the bearing is gliding to the spindle end and afterwards loosing contact to the spindle - I would definitely fix the inner race to the spindle end!!!
    Why reach for speed, when you could have precision instead!!!

  3. #3
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    Feb 2009
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    See the problem is this, the bearing block was designed to use these cheap skate bearings. These bearings are not designed for thrust applications. When used in this way the inner race is deflecting just a little bit. It is a design flaw but I'm sorta stuck as I do not want to redesign my entire drive line to use proper thrust bearings but I may have to as I cannot find thrust bearings the same size as these litle buggers.

  4. #4
    Join Date
    Mar 2003
    Posts
    35538
    What's keeping the screw from moving? The motor coupler? If so, that's a bad design, and will ruin the motor bearings.
    I use two skate bearings blocks back to back, so the nut holds the bearings and blocks together and the two bearings handle the thrust load. Tightening the nut preloads the bearings. My blocks are made of phenolic, si I glued them together into a single block.
    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)

  5. #5
    Join Date
    Feb 2009
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    1290
    There is a bearing block with a skate bearing at each end of the screw Gerry. They attach down to the machine and prevent the screw from moving but the bearing's inner race has a slight give when pushed on...

  6. #6
    Join Date
    Jul 2007
    Posts
    177
    Running a long spindle on high speeds expand the spindle by expansion coefficient using your bearing system may damage the bearing just and only by temperature and expansion related to this.


    There is a very coarse " rule " inner race / shaft diameter multiplied by three
    is about the axial force a bearing can have applied before being damaged

    A radial bearing ( also a skater bearing) has about 6 to 8 mm shaft diameter *3 means you can apply about 18 to 24 N without damaging (dependent on the bearing topology and the amount of balls used) - more exact values are to be taken from the Axial Cstat parameter) a simple 2 Nm Motor with a 12x3 spindle produces far more than 1000 N axial force a diagonal bearing made in China is about 8 to 10 Bucks use 2 countermounted 10x30 ones in "o" arrangement and you are rather rid of that problem...
    Why reach for speed, when you could have precision instead!!!

  7. #7
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    Feb 2009
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    1290
    Thanks for the reply Harpye, these bearing blocks are being used on my ACME screws not a spindle. I like your calculations on max loading maybe I can use a system like Gerry has with 2 bearings. Do you have a diagram of the "o" arrangement?
    Gerry do you have a picture of your bearing block mounts?

  8. #8
    Join Date
    Jan 2005
    Posts
    67
    IT apears that you need to add thrust bearing to the radial bearing shown. they are very thin and they will allow the lead screw to anchor to the bearing block and not th innner race.

  9. #9
    Join Date
    Feb 2009
    Posts
    1290
    yep john, or replace the radial bearing all together. I found some that were close on vbx bearings .com. 10x24x4 @ $2.65ea while a standard skate bearing is 8x22x7.
    I would have to get the bearing block's diameter increased by 2mm and the shaft would need a 2mm sleeve.

    I should note, this bearing block system is being sold on ebay and through a web site. I have been in direct contact with the sellers before and I will let them know about the design revision needed to fix this issue.

  10. #10
    Join Date
    Jul 2007
    Posts
    177
    Drool ... Sry - in German SPINDEL means Thread but also the Milling Spindle

    Did you buy a fix bearing block or a loose side block???



    Try the following

    let's say you have 1Nm Stepper Motors and a 12mmx3mm ACME Thread

    1Nm divided by effective radius of your Tread - let's assume that it would be 6mm

    1Nm/0.006m means you have a tangential force of about 166.6N

    not concerning about friction losses of your thread and assuming a 100% efficiency as a worst case

    you now shoud calculate the effective length of your effective tread diameter

    means PI*d = PI * 12mm = 37.7mm


    the ratio between this and the thread height means the force to way transmission of your tread gear

    = 37.7 / 3 = 1: 12 What means Axial force = Tangential force *12

    Axial force = 1666 N ~ 166,6 KG of weight ...

    Now you would need bearings to bear this!!

    I would recommend 10X 30 diagonal bearings ( Google for Bearing and 7200) ( mounting direction is important and you need 2 for one fix bearing block - you may use what you have but for the loose bearing side there you just would need a supporting bearing which takes no axial load / which is not axially locke to the block!)

    "o" or "X" arrangement means the appearance of the force / connective lines through the bearing system

    ALways remember to go for Shoulder / diagonal bearings to aker that huge force / load


    http://www.mixware.de/bilder/b42.jpg

    Left is the x arrangement right the o

    I use those ... This type is a selection for paired assembly - for a special way of assembly which creats a geometry defined preload having no play under normal conditions - but they are 3x more expensive due to the selection
    Attached Thumbnails Attached Thumbnails DSC07837.JPG  
    Why reach for speed, when you could have precision instead!!!

  11. #11
    Join Date
    Feb 2009
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    1290
    sorry these are the ones I'm looking at.
    Thrust Needle Roller Bearing 10x24x4:Ball Bearings

    These ones have a higher load rating for about the same money.
    http://www.vxb.com/Merchant2/merchan...t_Code=Kit7593

  12. #12
    Join Date
    Jul 2007
    Posts
    177
    OUUUUCH!!!

    Those are pure axial bearings - do what you want but that is just applicable with additional radials or shoulder types to keep the spindle weight in place

    those are ABSOLUTELY NOGO for stand alone use in your case!!!

    Not to offend you but better you would read the application notes at for e.g. SKF and afterwards come back with questions ...

    Or google for Thread end bearing

    To give you an intension

    http://www.google.de/imgres?imgurl=h...MJDXsga7ksixCA

    the top left bearing is a typical simplex " o" arrangenment for the fixed side block righ hand there is a Duplex unit for higher loads - needs much more precision in parts and assembly
    the 2 row bearing is someway expensive due to construction and assembly issues but can be replaces by 2 single row shoulder / diagonals which are created for paired assembly - those I have shown above...

    But this is a very special variant of the 10x30 / 7200 type ... you are not able to pair every skind of this bearing in this way for normal assembly with a flange shoulder in between you need to set the bearings forceless ( have a play fitting so the bearings are shiftable) and tighten them with a torque wrench to specified tension ... difficult thing!!!
    Why reach for speed, when you could have precision instead!!!

  13. #13
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    Feb 2009
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    Not offended Harype. I'm just trying to figure this out.
    I picked that type of bearing because I have seen a very popular company sell the same thing with their 80/20 CNC kits. We are just talking about bearing blocks for hobby use on the ends of ACME 1/2-10 2 start screws right?

  14. #14
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    Jul 2007
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    177
    Here is some datasheet for the 7200 series...

    when assembled correctly the 10x30 is able to withstand a axial force of about more than 10 KN ( cstat) I calculated ( as an example an axial force of 1.666kN ... so for my assumption this bearing would have a overcapability of about 6 to 7

    SKF - Produktdaten

    I don't know the US Norms regarding Threads ... so take my calculation and just insert your parameters
    Why reach for speed, when you could have precision instead!!!

  15. #15
    Join Date
    Jul 2007
    Posts
    177
    A hobbyist machine has also to be functional ... the more as a hobbyist is not able to effort additional measures against overload

    Are you available via skype ...you could send your Nick and I'd give you a little update!
    Why reach for speed, when you could have precision instead!!!

  16. #16
    Join Date
    Aug 2008
    Posts
    1166
    Yes, those thrust bearings would work as long as you provided surfaces for the washers to rest on. For example the cncrouterparts' block has a cover plate that bolts to the bearing block to cover the radial bearing so the thrust bearing's washer is not resting against the radial bearing's inner race (as that would defeat the purpose). If you do use these types of thrust bearings, I'd recommend radially locating the thrust washers that sit against the bearing block somehow. Mine shifted off center on my Y axis and ground a groove in my lead screws. I used a few dabs of super glue to fix it to the bearing block and keep it centered around the screw shaft. A machined pocket in the block would be the more professional way to go.
    CNC mill build thread: http://www.cnczone.com/forums/vertical_mill_lathe_project_log/110305-gantry_mill.html

  17. #17
    Join Date
    Feb 2009
    Posts
    1290
    What do they say, "pictures speak 1000 words"
    Here are some pictures.
    Attached Thumbnails Attached Thumbnails DSCF0001.jpg   DSCF0002.jpg   DSCF0003.jpg   DSCF0004.jpg  

    DSCF0005.JPG   DSCF0006.JPG  

  18. #18
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    Feb 2009
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    More pics
    Attached Thumbnails Attached Thumbnails DSCF0007.jpg   DSCF0008.JPG   DSCF0009.JPG   DSCF0010.JPG  

    DSCF0014.jpg   DSCF0015.jpg  

  19. #19
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    Feb 2009
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    two more
    Attached Thumbnails Attached Thumbnails DSCF0016.jpg   DSCF0017.jpg  

  20. #20
    Join Date
    Mar 2003
    Posts
    35538
    Quote Originally Posted by Drools View Post
    Gerry do you have a picture of your bearing block mounts?
    http://www.cnczone.com/forums/118161-post66.html

    http://www.cnczone.com/forums/attach...4&d=1248048047
    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)

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