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  1. #1
    Join Date
    May 2006
    Posts
    309

    Milling spheres?

    Have anybody here created a perfect round sphere by using the sphere code generator in order to create a half sphere first and then turn it around for completing the work? And are the ball mills that are for sale on ebay good enough for this purpose or do I need a perfectly grinded ball mill?

  2. #2
    Join Date
    Jun 2015
    Posts
    4131

    Re: Milling spheres?

    hi jaru-eri

    perfect round sphere
    this perfection depends on cnc accuracy ( available & output ) and backlash management

    even if you have a pretty accurate cnc, you should still consider to control :
    ... axis reversal ( near the top of the sphere )
    ... accuracy value

    example of backlash management functions, for okuma :
    ... ( variable ) lost motion compensation
    ... pitch error compensation
    ... reversal spike auto-adjustment

    example of accuracy control, for okuma :
    ... in-position parameter
    ... nurbs
    ... allowable errors in radius comp & in circular interpolation
    ... acceleration / deceleration

    also, a complex shape requires moderate feedrates, because higher values will lead to deviations

    create a half sphere first and then turn it around for completing the work
    i am afraid that you won't obtain a nice sphere if you go like that

    pls check video shared in this post :
    ... roughing is done on each half
    ... part is rotated with 90*, and roughing is repeated
    ... if you wish, you may repeat the process also at 45 90+45 180+45 and 270+45 degrees
    ... part is rotating during the pre-finish and the finish operations


    obviously, turning seems to be more indicated, or at least a vmc with 4th axis

    do you wish to know how balls of bearings are turned ? there is an insert for hard turning, and the ball is between 2 centers with spherical surface; in the end, the ball is reclamped in a rotated position, so to turn the material that was making contact with those spherical centers at the previous operation

    And are the ball mills that are for sale on ebay good enough for this purpose or do I need a perfectly grinded ball mill?
    if you wish only to experiment, you don't need expensive tools no ....

    all you need is to adjust the cutting specs : for example, if you clamp a tool and it has 0.04tir, simply don't use a finishing feed > 0.04 / does it makes sense ? consider feed=60%tir; if you go like that, you should end up with a nice smooth surface

    if the surface is smooth, uniform, than measure spherical tolerance, so to see how close you are to a sphere : in this moment, if you are not satisfied, repeat the process with a higher quality tool ( from better carbide, with better coating and with better goemetry ), and clamp that tool with less tir : now you should see better results

    kindly


    https://www.youtube.com/watch?time_c...&v=NwOtZnjqKGA
    Ladyhawke - My Delirium, https://www.youtube.com/watch?v=X_bFO1SNRZg

  3. #3
    Join Date
    May 2006
    Posts
    309

    Re: Milling spheres?

    Ok. I understand. But with all that difficulties, maybe it will be an easier and better choice to make the sphere in a manual lathe with a rounding tool instead?

  4. #4
    Join Date
    Dec 2013
    Posts
    5717

    Re: Milling spheres?

    Quote Originally Posted by jaru-eri View Post
    Ok. I understand. But with all that difficulties, maybe it will be an easier and better choice to make the sphere in a manual lathe with a rounding tool instead?
    Using a lathe with a radius turning tool might be the best choice. A CNC lathe makes it very easy.




    Jim Dawson
    Sandy, Oregon, USA

  5. #5
    Join Date
    Jun 2015
    Posts
    4131

    Re: Milling spheres?

    hello again jaru those are not dificulties, but cnc related stuff when machining a sphere

    pls try not to look at them like being dificulties, and give up, so to chose a classical lathe

    classic and cnc have a lot of things in common



    about classic : you may also consider a copy lathe, or a dedicated holder, like jim dawson said
    about cnc : is pretty easy to turn a sphere; just go and try / kindly
    Ladyhawke - My Delirium, https://www.youtube.com/watch?v=X_bFO1SNRZg

  6. #6
    Quote Originally Posted by deadlykitten View Post
    hi jaru-eri



    this perfection depends on cnc accuracy ( available & output ) and backlash management

    even if you have a pretty accurate cnc, you should still consider to control :
    ... axis reversal ( near the top of the sphere )
    ... accuracy value

    example of backlash management functions, for okuma :
    ... ( variable ) lost motion compensation
    ... pitch error compensation
    ... reversal spike auto-adjustment

    example of accuracy control, for okuma :
    ... in-position parameter
    ... nurbs
    ... allowable errors in radius comp & in circular interpolation
    ... acceleration / deceleration

    also, a complex shape requires moderate feedrates, because higher values will lead to deviations



    i am afraid that you won't obtain a nice sphere if you go like that

    pls check video shared in this post :
    ... roughing is done on each half
    ... part is rotated with 90*, and roughing is repeated
    ... if you wish, you may repeat the process also at 45 90+45 180+45 and 270+45 degrees
    ... part is rotating during the pre-finish and the finish operations


    obviously, turning seems to be more indicated, or at least a vmc with 4th axis

    do you wish to know how balls of bearings are turned ? there is an insert for hard turning, and the ball is between 2 centers with spherical surface; in the end, the ball is reclamped in a rotated position, so to turn the material that was making contact with those spherical centers at the previous operation



    if you wish only to experiment, you don't need expensive tools no ....

    all you need is to adjust the cutting specs : for example, if you clamp a tool and it has 0.04tir, simply don't use a finishing feed > 0.04 / does it makes sense ? consider feed=60%tir; if you go like that, you should end up with a nice smooth surface

    if the surface is smooth, uniform, than measure spherical tolerance, so to see how close you are to a sphere : in this moment, if you are not satisfied, repeat the process with a higher quality tool ( from better carbide, with better coating and with better goemetry ), and clamp that tool with less tir : now you should see better results

    kindly


    https://www.youtube.com/watch?time_c...&v=NwOtZnjqKGA
    Hey deadly kitten I’m currently undergoing this task in work.

    Attempting to turn a sphere on a cnc lathe. The video you’ve attached doesn’t work any more; do you know of a similar video or know where I can access this video.

    We’re having trouble holding the sphere for the 2nd operation.

    Thank you in advance.

    Kind regards,

    Bradley.

  7. #7
    Join Date
    Apr 2004
    Posts
    5728

    Re: Milling spheres?

    [QUOTE

    We’re having trouble holding the sphere for the 2nd operation.

    [/QUOTE]

    That's always going to be a problem if you really need a complete sphere, not just a sphere on a stick. You either have to make a fixture that will hold the spherical part -
    like 2 plates with spherical divots opposite one another that you can clamp together and hold onto so that the stub end sticks out for machining - or do something like the procedure outlined above for making ball bearings.
    Andrew Werby
    Website

  8. #8
    Join Date
    Jun 2015
    Posts
    4131

    Re: Milling spheres?

    hi, i just checked, and that video had been removed; it was about milling a sphere ...

    We’re having trouble holding the sphere for the 2nd operation
    pls develop ...

    i suppose you turned a part of that sphere in 1st operation, and now you wish to finish it, and the 2nd operation does not has a good fixture ? maybe you can share an image with the sphere after 1st operation, and the clamping of the 2nd operation / kindly
    Ladyhawke - My Delirium, https://www.youtube.com/watch?v=X_bFO1SNRZg

  9. #9
    Join Date
    Dec 2013
    Posts
    5717

    Re: Milling spheres?

    What size sphere? What is perfect for you?

    We CNC one part that has a sphere on the end but has a stem to hang on to for the second op. In the first op you would have to cut about 60% - 70% of the sphere, then for the second op you would need a special collet or soft jaws that would form fit the sphere and be able to grab it over center to hang on to it.

    If you really need it to be ''perfect'' then you have to process it like a ball bearing with a special machine.
    Jim Dawson
    Sandy, Oregon, USA

  10. #10
    Join Date
    Jan 2005
    Posts
    15362

    Re: Milling spheres?

    Quote Originally Posted by deadlykitten View Post
    do you wish to know how balls of bearings are turned ? there is an insert for hard turning, and the ball is between 2 centers with spherical surface; in the end, the ball is decamped in a rotated position, so to turn the material that was making contact with those spherical centers at the previous operation
    That is total BS

    Balls for Bearings are cold headed into a rough ball shape and then they are rough cleaned up, then heat treated they are then ground, then lapped to finial finish and size, they are never turned in any way here is two snips of roughly how ball bearings are made
    Mactec54

  11. #11
    Join Date
    Sep 2014
    Posts
    129

  12. #12
    Join Date
    Aug 2009
    Posts
    1566

    Re: Milling spheres?


  13. #13
    Join Date
    Jun 2015
    Posts
    4131

    Re: Milling spheres?

    Quote Originally Posted by mactec54 View Post
    That is total BS

    Balls for Bearings are cold headed into a rough ball shape and then they are rough cleaned up, then heat treated they are then ground, then lapped to finial finish and size, they are never turned in any way here is two snips of roughly how ball bearings are made
    hy mactec, technology for crafting the ball is not unique for the entire size range; frequent sizes are smaller, so there is justified a punch-forming machine

    also, what i have described is not a full process; what about cold/hot forging the ball + hard turning + grinding & sorting ( 2-3 baths ) + lapping ( 1-2 baths )

    maybe you should try a ball bearing ... kindly
    Ladyhawke - My Delirium, https://www.youtube.com/watch?v=X_bFO1SNRZg

  14. #14
    Join Date
    Dec 2008
    Posts
    3110
    Quote Originally Posted by Jim Dawson View Post
    If you really need it to be ''perfect'' then you have to process it like a ball bearing with a special machine.
    Do we blame Jim for mentioning "ball bearings" ?
    ....or the other 2 for arguing about something off topic ?

    No-one knows if it is a true sphere (size ?), or something like a towball...

    Kitty... keep it on topic, stop making it over complicated

  15. #15
    Join Date
    Jun 2015
    Posts
    4131

    Re: Milling spheres?

    No-one knows if it is a true sphere (size ?), or something like a towball...
    maybe is a towing hitch ....
    Ladyhawke - My Delirium, https://www.youtube.com/watch?v=X_bFO1SNRZg

  16. #16
    Join Date
    Jan 2005
    Posts
    15362

    Re: Milling spheres?

    Quote Originally Posted by deadlykitten View Post
    hy mactec, technology for crafting the ball is not unique for the entire size range; frequent sizes are smaller, so there is justified a punch-forming machine

    also, what i have described is not a full process; what about cold/hot forging the ball + hard turning + grinding & sorting ( 2-3 baths ) + lapping ( 1-2 baths )

    maybe you should try a ball bearing ... kindly
    I know what Ball Bearings are I used to build custom protype Bearings for SKF , they are never hard turned as you say
    Mactec54

  17. #17
    Join Date
    Jun 2015
    Posts
    4131

    Re: Milling spheres?

    this is a fact, from a plant : technology for crafting balls involved forging from dia~25, and hot forging from dia~60 to over100

    forging operations are followed by turning in 1 or 2 steps : removing burs + kind of prefenish, before grinding operations

    okey, now what ?

  18. #18
    Quote Originally Posted by Jim Dawson View Post
    What size sphere? What is perfect for you?

    We CNC one part that has a sphere on the end but has a stem to hang on to for the second op. In the first op you would have to cut about 60% - 70% of the sphere, then for the second op you would need a special collet or soft jaws that would form fit the sphere and be able to grab it over center to hang on to it.

    If you really need it to be ''perfect'' then you have to process it like a ball bearing with a special machine.
    Thank you for all of your reply’s.

    I don’t have a picture at the moment because I’m not in the factory as it’s the weekend in the UK. But I do have a picture of something similar that I’ve found from another thread. (Which I will attach)

    I want to turn it to a tolerance of around 2 thousands. But I’d be happy with 5 thou all the way around or even more.

    However that isn’t my main aim at the moment, holding the work for the 2nd operation is my main concern.

  19. #19
    Quote Originally Posted by Jarith1993 View Post
    Thank you for all of your reply’s.

    I don’t have a picture at the moment because I’m not in the factory as it’s the weekend in the UK. But I do have a picture of something similar that I’ve found from another thread. (Which I will attach)

    I want to turn it to a tolerance of around 2 thousands. But I’d be happy with 5 thou all the way around or even more.

    However that isn’t my main aim at the moment, holding the work for the 2nd operation is my main concern.
    Here is the attached image. Of a slug that someone else has turned so far.

    And the ball im looking to make is a 30mm ball (a perfect sphere with no holes etc to attach a stem)

    I’ve seen a few videos of people rough lapping on machines following a chamfer and pressing process.

    But ideally I want to do this on the cnc.

    The cnc we have at the factory is a haas sl20 if you’re wondering.
    Attached Thumbnails Attached Thumbnails A64C6814-C52A-4D53-A3A5-21B2EA2807FF.jpg  

  20. #20
    Join Date
    Dec 2013
    Posts
    5717

    Re: Milling spheres?

    Quote Originally Posted by Jarith1993 View Post
    Here is the attached image. Of a slug that someone else has turned so far.

    And the ball im looking to make is a 30mm ball (a perfect sphere with no holes etc to attach a stem)

    I’ve seen a few videos of people rough lapping on machines following a chamfer and pressing process.

    But ideally I want to do this on the cnc.

    The cnc we have at the factory is a haas sl20 if you’re wondering.
    OK, that information gives us something to work with. 2 thou roundness tolerance and 30mm dia. I was thrown off by your use of the word ''perfect'', to me that means sub-micron precision.

    As I said above, do the first op at about 60-70% of the sphere, then make soft jaws that form fit the finished portion to hold for the second op. There is no way to do this in one operation. Your sl20 should be more than capable of doing this.
    Jim Dawson
    Sandy, Oregon, USA

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