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Thread: ER 40 Collet taper

  1. #1
    Join Date
    Nov 2014
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    4

    Default ER 40 Collet taper

    I'm new to the site and did a search on the site and google to find the best way to cut an internal 8/9 degree internal taper for an er 40 collet.
    Got some simple plans, but what the easiest way to cut the internal taper. Is there a large taper ream or do I use the compound/cross slide method and lap and polish the taper to fit the collet, I am using Aluminum for the holder since I will be using the collet periodically.

    Regards,

    Bill

  2. #2
    Join Date
    Mar 2001
    Location
    Nottingham, England
    Posts
    15,403

    Default

    Compound / cross slide and polish up.
    It's a dead 8 degrees BTW
    .

    Sir John , Earl of Bligeport & Sudspumpwater. MBE [ Motor Bike Engineer ] Nottingham England.




  3. #3
    Join Date
    Nov 2014
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    4

    Default

    John,

    Thanks, however I have read that the 8 is sometimes 9, although in 1.37 inches or so 1 degree wouldn't mount to too much.

  4. #4
    Join Date
    Mar 2001
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    Nottingham, England
    Posts
    15,403

    Default

    It does matter. ER32, R8 and ISO 30 tapers are all within 1/2 a degree of one another and none fit each other correctly and yes the taper is 8 degrees dead on.
    Whoever said 9 doesn't know what they are talking about.
    .

    Sir John , Earl of Bligeport & Sudspumpwater. MBE [ Motor Bike Engineer ] Nottingham England.




  5. #5
    Join Date
    Jan 2010
    Location
    Kansas City area
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    3,470

    Default

    Just so you know Bill - John DOES know what he's talking about. He is the guy to listen to.

  6. #6
    Join Date
    Nov 2014
    Posts
    4

    Default

    Thanks for all the advise, John NO offense intended. If it is 8, it is 8. I had plans and commentary which the writer said 8 was actually 9, may be he got a bad collet. I'll use 8 go with it.
    Thanks again ,
    Bill
    Last edited by just bill; Today at 04:56 AM. Reason: auto spell/correction error

  7. #7

    Default

    If your taper is anything other than dead on 8 degrees, you will find that the workpiece can wiggle a little because either the front end or the back end of the collet can move in the holder. Just close isn't good enough. If you have .001" too large at either end your workpiece can be several thousandths out two or three inches away.

    Don't be overintimidated by that because if you find it's off a little you can adjust the compound and finally polish a tiny bit out at the end. You've got lots of chances to adjust and re-cut till it's right. However, don't plan on polishing much out because it's easy to get a bellmouthed condition which also won't register properly.

    Since you already have ER-40 collets on hand (I presume), you would be able to chuck a piece of stock, turn it to a close fit for one of the collets, put a collet on the mandrel you've just machined and then mount an indicator on the compound to see if it's tracing the collet accurately.
    .
    "Opportunity is missed by most people because it is dressed in overalls and looks like work." Thomas Edison

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