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Thread: About how much torque should an R8 Drawbar have?

  1. #1
    Join Date
    Jan 2004

    Default About how much torque should an R8 Drawbar have?

    Gents--there are times when I think I am over tightening a collet or arbor for a R8 Spindle Vertical Mill. About how much "tightening" or torque should it take?

    As always, thanks for sharing your expertise.

  2. #2
    Join Date
    Jul 2005
    Burnet, TX


    I don't have a torque value but they don't have to be all that tight. I snug things up and then give a tug on the wrench to get 1/2" or so of additional movement. I probably tighten drills larger than 3/4" a little tighter.
    Byron Boucher
    Burnet, TX

  3. #3
    J.Ramsey Guest


    I have my air powered draw set at 25 ft.lbs. Checked with a torque wrench.

    Haven't slipped or stuck a collet yet.........

  4. #4
    Join Date
    Nov 2009
    Winchendon MA


    1/2 turn less than striping the threads, couldn't resist ha ha.

  5. #5
    Join Date
    Dec 2004
    Western New York U.$.A


    I put my import mill in lowest gears, snug it down hard with wrist action and then pull it back with my shoulder till the quill starts to turn. I do not use a second wrench in my other hand. So far, after all my dinking around, I've not had a collett spin in the quill nor a bit in the collett. Once they start spinning your on the highway to hell !!
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  6. #6
    Join Date
    May 2006


    Its independent to the size of the endmill or tool your using,

    All collets (from the same machine) have the identical leverage ratio (the outside of the collet against the spindle bore taper),

    what this means is this force then gets transferred directly to the cutting tool,

    So --- all you really need for a 1/8" endmill is a mild cinch up since not only is the leverage compounded to such a small surface area (high unit pressures)
    The cutters radius and strength itself has minimal holding requirements

    Every cutter need's to have its torque adjusted to meet its needs,
    Save the drawbar threads for when you chuck up your 3/4" endmill --- flycutter --- or 5" R8 three jaw chuck....

    This is why (or just one of the reasons actually) I don't own a power drawbar and never will - I like using only what I need --- it also saves collet and spindle bore wear...

  7. #7
    Join Date
    Feb 2009
    Northern Indiana


    I simply send the bolt home, and then slap the wrench a couple of times with an open hand.

    If the taper is true and seats correctly, it should take virtually 100% of the torque anyway. There should be no real load on the drawbar, other than if you are performing an operation that is trying to pull the tool holder out.

    This is purely my opinion. I am NOT a know-it-all.


  8. #8
    Join Date
    Aug 2005
    shreveport La


    Until you can`t tighten it any more,with the supplied wrench.

  9. #9
    gnm109 Guest


    I use the brake on the Webb Mill to hold the spindle from moving when tightening or loosening a collet. I tighten them up until I can feel that the collet has seated nicely. Another inch or so on the wrench and I'm done.

    To remove, I lock the spindle and use a dead-fall hammer to tap the top of the drawbar. Works for me.

    I'm also very careful to make sure that there is no grit on the collet before I insert it into the spindle. A wipe with an oily rag will help.


  10. #10
    Join Date
    Mar 2005
    Palmer Alaska


    The Bridgeport Operators Manual, Bridgeport developed the R8 taper....

    They just might know something about it.

    Clearly states "The drawbar should be tightened with a NORMAL amount of pressure using wrench furnished with machine."
    Last edited by Bguns; 11-07-2010 at 05:35 PM.

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