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  1. #1
    Join Date
    Jul 1999
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    St Ives, Sydney,NSW,Australia
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    33

    Default Shaft size for 12mm bearing?

    I need to order a shaft that will be ground to size to fit a 12mm (id) x 10mm x 32mm bearing.

    As I don't want to order the wrong size and never having done this before what diameter should I be specifying for a press fit tolerance on the 12mm bearing?

    Does some rule of thumb exist for this type of thing?

    Thanks

    Warren

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  3. #2
    Join Date
    Sep 2006
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    Australind ,WA
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    Default Shaft size for 12mm bearing?

    Any decent mechanical fitter should be able to tell you that, for certain. Or you could do some googling and research the different types of clearance and interference type 'fits' for this type of application.
    I'm not a MF but I have heard mumblings of a figure of 2 thou interference for this sort of thing. This equates to 0.05 mm so the shaft would have to be 12.05 mm in diamtre.
    Another option would be to gain access to a lathe and do some experimenting yourself. At least that way, there is a good chance you won't forget it for next time.

  4. #3
    Join Date
    May 2005
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    Default

    I seem to remember 4 thou to the inch, that would be 2 thou to 12mm heat the bearing in an oven 200 deg at least, unless you have a bearing induction heater , but be careful if its a sealed bearing and the bearing should slide on easily .

    Rgds
    Ashore




    The trouble with life is there's no background music.

  5. #4
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    Sep 2006
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    Australind ,WA
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    "heat the bearing in an oven 200 deg at least"

    Don't heat a bearing to over 100 degrees C. Around 80 to 90 is a safer temperature range.

  6. #5
    Join Date
    Feb 2007
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    Katherine ,Northern Territory
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    Default

    Quote Originally Posted by Sterob View Post
    "heat the bearing in an oven 200 deg at least"

    Don't heat a bearing to over 100 degrees C. Around 80 to 90 is a safer temperature range.


    And you can put the shaft in the freezer also .
    "Outside of a dog a book is man's best friend ,inside a dog it's too dark to read"
    Groucho Marx

  7. #6
    Join Date
    Jun 2005
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    Helensburgh
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    Default

    Quote Originally Posted by Sterob View Post
    "heat the bearing in an oven 200 deg at least"

    Don't heat a bearing to over 100 degrees C. Around 80 to 90 is a safer temperature range.
    Get a bit smelly to as the grease starts to melt. SWMBO will not be to pleased I would think, best to freeze the shaft and use a bit of force to get the bearing on.
    CHRIS

  8. #7
    Join Date
    Oct 2006
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    Tallahassee FL USA
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    4,650

    Default

    Class of fit relates tolerances on both the hole and the shaft. For "medium drive" interference fit on 12mm nominal, ANSI B4.2-1978 advises hole at 12.000 to 12.018mm, shaft from 12.028 to 12.039mm. BS 4500:1969 has similar relationships, but different nomenclature. (ref: Machinery's Handbook) Wouldn't hurt to consult a pro.

    Joe
    Of course truth is stranger than fiction.
    Fiction has to make sense. - Mark Twain

  9. #8
    Join Date
    Jan 2006
    Location
    Victoria
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    58

    Default Herro, Missa.

    Bean an Ingineer, building great walls to keep out the rabbits etc., to keep the rabbits out;

    Akshoolee, building plain shafts for most bearings is pretty easy.

    1/2 the job is working out what kind of a fit you want, 1/2 the job is looking up the INTERFERANCE FIT tables (designed by idiots) and the last 1/2 of the job is doing it.

    OD = Outside Diameter, ID = Inside Diameter.

    Ok simplified - it's sort of like this.

    This is not the ideal situation but it's a bench mark.

    Imagine a 20.000mm OD shaft... it would be an exact fit into a bore that was 20.000 ID.

    It's an exact fit.

    We have kind of 3 types of FITS, depending upon application.

    The first kind of a fit, is a LOOSE fit

    The bore has a larger ID than the shaft's OD, or the shaft's OD, is smaller than the bore's ID.

    The second kind of a fit is called an ACCURATE (or smooth running) fit.

    The bore's ID and the shart's OD are pretty much the same.

    The third kind of a fit is called an INTERFERANCE fit.

    Then we have the bore's ID is smaller than the shaft's OD or the shaft's OD is larger than the bore's ID.


    These terms are used in production engineering in this way.

    Think about using nice sharp tools to make 10,000 shafts and 10,000 bores, to make 10,000 assemblies, that have a smooth running fit.

    See the very switched on places, do all the compensation for wear of the tools etc., and do the manufacturing like this.

    As the boring tools are fresh and sharp the first bores will be a bit too small and the last bores will be a bit too large, because of the wear on the tools.

    The first shafts will be a bit too small and the last ones will be a bit too large.

    By matching the first shafts with the last bores and working back, till the last shafts are mixed with the first bores; in a simple sense, all the clearances, should be the same.

    The shafts should all be smooth running fits in the bore.

    That's the tolerances in use in production engineering.


    Now.... the situation for locating ball bearings on shafts is this.

    Most ball bearings are fairly accurate, as far as tolerances go. The bores and OD's tend to be perhaps within 0.000X mm of the right size + or - 0.000xxmm.

    What we have in terms of tolerance is the bearing will either be a loose fit in the shaft, a nice running fit, or a tight fit.

    If you need a loose fit, then that's easy to make. But if you need an interference fit, the question is what kind of an interferance fit, and what is the application?

    This is for you to decide.

    All the factors such as cost, RPM, load (weight) and load type (axial, radial and combined), lubrication types, and durability of the unit come into play.

    One does not put super precision bearings and shafts in a wheel barrow wheel and one does not put ?????? loose pressed ball, ball bearings in a super expensive high speed machine.

    So there is not really a concept of "the right thing" it's a matter of tradeoff's to get the best outcome, for the minimum cost, to produce the best result.

    Your bearing and shaft kind of have to meet the parameters of the design.

    The interferance fit is like this.

    (sort of making this up a bit to illustrate the point)

    Say we have a 19.985 - 19.990mm shaft and a 20.000 bore....

    This is called a precision running fit.

    If we increase the diameter of the shaft to 20.000 then we have an exact fit.

    If we increase the shaft diameter to 20.010 we have a hand fit - where the resistance of squeezing the bearing onto the shaft can be done by hand alone.

    If we increase the shaft diameter to 20.100 we have a hand press fit - where the resistance of squeezing the bearing onto the shaft can be done by light pressure in a hand hydraulic press.

    If we increase the shaft diameter to 20.500 we have a press fit - where the resistance of squeezing the bearing onto the shaft can be done by either a hand press or a mechanical press.

    Etc.

    The same situation exists for the outside of the bearing.

    When the issue of interference fits arises....

    If under some circumstances either the shaft or the bearing is gripped too loosely (not enough interferance) the shaft or bearing may work loose.

    Ball bearings (the races) are both compressible and expandable.

    If the bearing has too big a shaft driven into it, it may depending upon the amount of stretching around the shaft, either have a short life or almost none at all...

    The same goes for the exterior of the bearing.

    There is an ideal kind of "too big shaft size" or "too small hole size" for the bearing (correct interference fit).

    If you go too much either way, the fit will be too loose or too tight.

    The outcome you want, is wholley job dependant.



    For example. my bike had the stupid design of having cheap ???? cup bearings and races, and the bearing on the right side of the axle, was about 50mm in from the chain stays, and this caused both regular bearing failure and bending of the axle.

    So Ineeded a better set up.

    The bearing/s in the hub were to be a permenent fixture and the compound axle (hollow) needed to be tight enough to make for as rigid an assembly as possible - BUT it had to be something that should it ever be required, it could be disassembled by hand on the side of the road.

    So I sized up everything, found I could get some neato SKF sealed bearings, the hub could be bored out and I could make up a hollow "compound" axle from 4140 alloy steel. The axle dimensions were about 17mm OD by about 220 long.

    The hole in the hub needed to be a little bit smaller than the 30mm OD bearings and as it was a permanent fitting, the hole needed to be fractionally tighter.

    The "compound" axle was to be a hollow axle to carry the radial loads, with a normal axle running through this, to clamp it in the frame.

    The hollow axle needed to be a kind of hard to firm hand only "press" fit inside the bearings.

    I can't quite remember all the exact sizes of everything, but I think the bearings were made to an exact and slightly tight fit on a 17mm shaft, so I made my shaft a little bit smaller.

    First I machined the hollow axle down to about 22 mm OD, then I bored it out slowly in many steps, with a long series drill, using lots of coolant.

    Then I located the hole in the shaft onto a DEAD (non spinning) center. I lubricated the center with a copper antiseize paste and I preloaded the center to act as a bearing, with a modest deflection preload, for light cuts with the lathe.

    I took the shaft down to about 18mm OD, then in very fine cuts, down to about 17.3mm. Then I honed the shaft down to about 17.08mm with a clogged up super fine swiss file.

    Then I lapped the shaft down with an abrasive stone down to about 17.02mm.

    After leaving a starting taper on the ende, I then lapped the shaft down with a wooden abrasive pad and some Brasso (or was it White Lilly cleaner?) and as I worked from one ende, I clean the axle, and then I'd press the bearing on by hand, and feel the amount of resistance as I forced it onto the shaft, and I slowly honed the shaft down to the same size along it's entire length, to give an exact, consistent hard hand only press fit.

    Now I have a back wheel that has 3 good sealed bearings in the hub, and it will last me for life, running on an axle that will never fail.

    (One bearing is in the left hand side of the hub, and two under the gears... one for the rolling load and the other for the drive load)

    Bingo!.


    Here is some stuff on the bearing fits.

    http://www.conweb.com/tblefile/bearfta.shtml

    http://www.wib-bearings.com/en/tech/tech_05.htm

    http://www.pacamor.com/shafthousing.php
    Last edited by 2shane; 10th April 2007 at 02:45 AM. Reason: I carnt spel lessera

  10. #9
    Join Date
    Feb 2006
    Location
    Perth
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    27,756

    Default

    Quote Originally Posted by Mini View Post
    Get a bit smelly to as the grease starts to melt. SWMBO will not be to pleased I would think, best to freeze the shaft and use a bit of force to get the bearing on.
    I use the BBQ for stuff like this and SWMBO doesn't seem to mind as the BBQ is my domain. I don't even have to use the whole thing as one of the BBQ burners heats a small cast iron oven and I can get that to 240oC without much trouble

  11. #10
    Join Date
    May 2003
    Location
    Southern Riverina
    Age
    75
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    36

    Default

    WOW!
    So many complicated answers.
    I've been a steel fabricator (my trade ) for 40 years and the easiest way to do this is to take the bearing to your local engineering workshop. Tell them what you want the bearing to do and ask for a bit of shaft suitable for the task required.

    Geoff P.
    When life hands you lemons.....
    "Pass the salt and where's the Tequila baby?"

  12. #11
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    Apr 2006
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    Toowoomba, QLD
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    Default

    How about just sliding it on and keeping it in place with a drop of Loctite?

  13. #12
    Join Date
    Nov 2006
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    Croydon, VIC
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    Default

    Loctite!? You butcher! (Just kidding, of course. If you're stuck between a rock and a hard place, sometimes its the only way.)

    Geoff's suggestion is an excellent one. If the fitter's that are making your shaft have the bearing in hand to take accurate measurements from, it'll save you a lot of time getting the shaft reworked to different sizes. (Especially considering you're not going to be able to measure microns with a $30 digital caliper from Bunnings.)

    Also consider that if you're going to have them chase a 2-3 micron tolerance, heat will change sizes by about 4-5 micron between a cold steel bench overnight and the heated lounge room. This is the biggest reason they'll need the bearing you want to use really. That way they can measure it at the same time in the same conditions as the shaft before machining. And as a bonus, they'll be able to check the fit at their end before sending you the shaft and bearing back.

    (Just telling it how I would at work.)
    'What the mind of man can conceive, the hand of a toolmaker can achieve.'
    Owning a GPX250 and wanting a ZX10 is the single worst experience possible. -Aside from riding a BMW, I guess.

  14. #13
    Join Date
    May 2003
    Location
    Southern Riverina
    Age
    75
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    36

    Default

    I'll bet that a standard stock item (steel shaft) will fit a 12mm bearing.
    When life hands you lemons.....
    "Pass the salt and where's the Tequila baby?"

  15. #14
    Join Date
    Apr 2007
    Location
    Geelong
    Posts
    48

    Default

    Quote Originally Posted by Geoff P View Post
    WOW!
    So many complicated answers.
    I've been a steel fabricator (my trade ) for 40 years and the easiest way to do this is to take the bearing to your local engineering workshop. Tell them what you want the bearing to do and ask for a bit of shaft suitable for the task required.

    Geoff P.

    Yeah what he said
    Long live the troopie, quads and welders

    and Go the mighty Saints (AFL)

  16. #15
    Join Date
    Jan 2006
    Location
    Victoria
    Posts
    58

    Default Umm a thort....

    It is possible to BUY some centreless ground steel shaft.... tho depending upon ones circumstances... whether the running around and all the ???????? justifies getting some accurately sized bar, vs making some up yourself...

    I should have kept my trap shut... on that point... the best way is to know the guys in the machine shops and what they are carrying.... other wise it can be a hassle....

    And most of the machining needs only a good vernier caliper... even a plastic one will do and then you can size the last 1/10th of a mm (or so) down by hand and feel...

    I mean I worked (or ran) the machine shop of a foundry and the booze soaked boss, expected me to machine the shafts for the switch gear, for the Alcoa smelting plant.

    However the machine shop was covered in foundry sand.. and the REALLY OLD 1932 lathe was SOOOOOOOOOOO WORN on the saddle, it had about a 1/2" drop on the bedway near the chuck..... the cross slide wasn't much better...

    This made it quite hard to machine the ~2 or 3" aluminium bronze shafts to an accurate diameter (within tolerances) to fit the ball bearings....

    I still managed to do most of the bearings pretty accurately... until the wino foreman got up me, and, "I said the lathe is junk and if your so ????ing good you do it - I then told him to stick the job up his ????.." - and I walked out.

    I am not working for booze soaked idiots on junk machinery.

    The hardest thing about creating new achievements, is to stop the habit of excuse making and to then do it.

    Research and Results.

    You can do almost anything you want.

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