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  1. #1
    I've been reading around and now I'm going through the process of trying to understand what I've read. I'd be really grateful for a bit of help with the following questions.

    I've been looking at the following axis design:
    Click image for larger version. 

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    (taken from CNCRouterParts.com)

    I'm trying to understand how the thrust bearings works in that setting? As far as I can tell, when assembled they would be in contact with the front/rear of the block not the radial bearing, so what would they achieve? The shaft collar is required here in order to keep the thrust bearings in place, would that be right?


    I was under the impression from reading around that a fairly solid bearing could be built using two angular contact bearings back-to-back (so the angles are directed outwards, effectively doing what I think the thrust bearings are meant to do in the picture above?), like so (cue rough and ready CAD):
    Click image for larger version. 

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    If so, as the bearings are constrained by the block, the shaft collar in the first picture would not be needed, is that correct?

    Also, are "angular thrust bearings" and "angular contact bearings" the same thing?

    Apologies for a lot of questions at once, this is largely new territory to me and I've got to the point where I've over-read my level of (current) undertanding. If I don't drag myself back to tackle what you all probably consider basics then I'll get completely lost and learn nothing!

  2. #2
    Quote Originally Posted by Rogue View Post
    I've been reading around and now I'm going through the process of trying to understand what I've read. I'd be really grateful for a bit of help with the following questions.

    I've been looking at the following axis design:
    Click image for larger version. 

Name:	exploded6.jpg 
Views:	1037 
Size:	57.7 KB 
ID:	4384
    (taken from CNCRouterParts.com)

    I'm trying to understand how the thrust bearings works in that setting? As far as I can tell, when assembled they would be in contact with the front/rear of the block not the radial bearing, so what would they achieve? The shaft collar is required here in order to keep the thrust bearings in place, would that be right?
    Ok well this part i can answer for you. this would appear to be the cheapest way to avoid the latteral load from the axis being transmitted into the Motor bearing. the fact that the drawing above does not show a ballscrew is a little missleading. ive just done a quick drawing in paint that may make things a little clearer notice i say "may"

    ....Click image for larger version. 

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ID:	4386

    And yes the thrust bearings would "be in contact with the front/rear of the block not the radial bearing"

    The radial bearing is not fixed to the drill rod but just a nice tight fit as a support for it. as you will know the shaft couplers are
    fixed to the rods they couple together, the simplest way is with grub screws, in turn these are mated to the outside of the thrust bearings respectively leaving no play if at all possible, this diverts the latteral load through the trust bearing into the radial bearing block and on through the chassis it is connected to and hopefully not on to the motor!!!

    there you go... Clear as mud

    Please remember im no expert so my terminology may not be as it should be but only enough to be understood....Maybe lol
    Last edited by Ricardoco; 28-08-2011 at 05:11 AM.
    Always bear in mind that your own resolution to succeed is more important than any other - Abe Lincoln

  3. #3
    A pair of, or a single double row angular contact bearing, is generally used to resist axial forces and eliminate end float. I think the problem with thrust bearings is they have to be mounted accurately - each side of the block they are mounted on must be parallel otherwise they will periodically bind. Angular contact bearings probably have a lower coefficient of rolling resistance, though I've not checked.
    Last edited by Jonathan; 28-08-2011 at 10:49 AM.

  4. #4
    Quote Originally Posted by Jonathan View Post
    A pair of, or a single double row angular contact bearing, is generally used to resist axial forces and eliminate end float. I think the problem with thrust bearings is they have to be mounted accurately - each side of the block they are mounted on must be parallel otherwise they will periodically bind. Angular contact bearings probably have a lower coefficient of rolling resistance, though I've not checked.
    Thats the word.. Axial... i just couldnt think what it was at 4 in the morning lol..

    As for type of bearing I think Jonathan has hit the nail on the head. from a self fabrication point of view, I found that angular contact bearings and the housings were easier to use.
    Always bear in mind that your own resolution to succeed is more important than any other - Abe Lincoln

  5. #5
    Quote Originally Posted by Ricardoco View Post
    ...this would appear to be the cheapest way to avoid the latteral load from the axis being transmitted into the Motor bearing. the fact that the drawing above does not show a ballscrew is a little missleading

    ...

    The radial bearing is not fixed to the drill rod but just a nice tight fit as a support for it. as you will know the shaft couplers are fixed to the rods they couple together

    ...

    there you go... Clear as mud
    Actually yes, that does make it a lot clearer! I was originally thinking in terms of a load perpendicular to the shaft which was probably what threw me. I'm currently considering starting with Acme thread which is why I was looking at that particular diagram.

    I was planning to just use the axis rather than introduce additional drill rod unless there is a good reason not to do so?

    Quote Originally Posted by Jonathan View Post
    A pair of, or a single double row angular contact bearing, is generally used.
    So one double row ACB (such as this: http://www.worldofcnc.com/products.asp?recnumber=147), or two back to back single row ACBs (such as these: http://www.worldofcnc.com/products.asp?recnumber=73) mounted in a block would perform that same function as the combination of elements discussed above?

    In the original block idea I posted (not the one from the website, mine) using two ACBs, would this mean that the load is being transferred into the coverplates that are holding the ACBs in place? And as they are pressing against the plates from the inside heading out, it would be the bolts holding the plates that are actually taking the strain? Number 1. in the picture below.

    Click image for larger version. 

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    If that's the case, presumably Number 2 would be a better option as the bearing block then takes the strain from the bearings.

    On a side note, I'm posting links to particular products that I'm looking at for the sake of clarity and safety - ie in case someone says "that bit doesn't do what you think it does, don't buy it" or "that really is too cheap to be worth using". It's not with any intention of advertising. I hope it's ok to do this

  6. #6
    The bearings should be like in 1. i.e pressing against the plates. Fix the bearing(s) to the end of the screw by having a thread and a nut on the screw to lock it in place.

    Those bearings you linked to are fine - but expensive! There's plenty on eBay...just search for the bearing number.

  7. The Following User Says Thank You to Jonathan For This Useful Post:


  8. #7
    Quote Originally Posted by Ricardoco View Post
    As for type of bearing I think Jonathan has hit the nail on the head. from a self fabrication point of view, I found that angular contact bearings and the housings were easier to use.
    If my current thinking is on-track then I'm hoping the basic homebrew block would look something like this:

    Click image for larger version. 

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  9. #8
    No, not like that. Move the 'wall' in the middle of the block to the edge, and have one plate on the other side to press the bearings against that. Have a look at the BK/BF blocks on eBay/Zapp if you're not sure...

    The way you've drawn it makes it harder to machine concentrically. The standard way only requires one hole to be bored.

  10. #9
    Jonathan, thanks for the quick reply, I need to learn to type faster!

    I'm surprised that No.1 would be the better option. May I ask why that is?

    If the screw has been turned down by that stage then would a shaft collar be sufficient for keeping it in place?

    Edited to add: and again with the fast reply! The single hole on one side was the original design idea, just like the other blocks I'd seen. The reason for trying to a different approach was because I thought they were using standard radial bearing in the block and thrust bearings on either side, and using the angular bearings would benefit from a different approach. Clearly not!

  11. #10
    Quote Originally Posted by Rogue View Post
    If the screw has been turned down by that stage then would a shaft collar be sufficient for keeping it in place?
    Possibly, but it's not ideal. The problem with a collar is, similar to the thrust bearings, it may be skewed on the shaft. A collar that clamps onto the shaft (ring with slit, bolt through slit to squash it) would be better. I would stick with having a thread. It depends what you're doing with the machine. If you're only cutting PCBs then pretty much anything will work ...

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