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How to fit oversize stock in 5C collets?

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  • How to fit oversize stock in 5C collets?

    Usually when I buy round stock, it manages to come out slightly oversize, e.g. 5/16=.314 and 3/4=.755. Sometimes it is a tight fit in a 5C collet, and sometimes it just won't go. I know that the grip range is not so large. What can I do?

  • #2
    Sometimes you can go up to the next-larger collet, in 1/64th inch increments. They do collapse by about .010" to .015".

    Better yet, just throw the 3-jaw or 4-jaw chuck on the machine?

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    • #3
      Are 5C collets available in metric sizes? If so might provide some in between sizes. Another solution would be to bore/grind some collets to enlarge their bores.

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      • #4
        Originally posted by beanbag View Post
        Usually when I buy round stock, it manages to come out slightly oversize, e.g. 5/16=.314 and 3/4=.755.
        Consider yourself lucky. The stuff we get is usually under size by 1 to 5 thou.
        :-( can't use it for shafts that go in bearings etc.
        ...lew...

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        • #5
          They are available in metric sizes, but they can be harder to find here, more expensive and usually only the whole number 1mm increments.

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          • #6
            isn't that nice of them including extra material! Hopefully the rolling mills won't borrow the nasty trick from pricks who make lumber and start making it undersized

            just get the next size up (1/64). Its a pita because you have to buy more collets....but its that or an emergency collet if you really need to hold them via collet. I've 2J (like 5c but a little bigger) and rubberflex collets; might seem like belt and suspenders but there are subtle differences when one will work and the other won't.....odd sized work like this is where the rubberflex shines so maybe long term that would a good shop addition
            in Toronto Ontario - where are you?

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            • #7
              "Stevenson's" ER32 / 5C collet adapter is one solution. Sounds like your need precludes the use of a normal 3-jaw---even if to only turn down a few inches on the bar end to nominal size? Otherwise for normal cold-roll steel, the stock tolerances are not so fine to generally gain any benefit from gripping in a collet rather than a three jaw scroll. Buying ground stock (which will be on size) is not always so much more costly than the cold-rolled. That is the other obvious solution.

              In general, though, in my personal shop I approach the problem in the following manner. I acquired a nice set of Hardinge 5C's with my lathe in 32nds. I later bought the absolute cheapest set of 64ths I could find. I've never given a second thought, consequently, to springing those. Fits the bill great for oversize, undersize or otherwise stock The Hardinge's, of course, are reserved for ground stock.
              Last edited by Arthur.Marks; 12-16-2012, 10:17 AM.

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              • #8
                May I ask why the use of collet on a material that is not on size? If I buy cold-drawn round stock, it is h9 or h11 tolerance, meaning +0 and -something, depending on the diameter. This fits in collets etc. and costs next to nothing. If one wants exact stuff, then ground material is a choice.
                Amount of experience is in direct proportion to the value of broken equipment.

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                • #9
                  I just use the next size up like someone else mentioned. They run in 1/64th increments and cover everything down to the next size. A 1/2" collet covers up to 1/2" period. If I don't happen to have the next size sometimes I'll turn it down in a chuck first, but only if I need to remove and reinstall repeatedley. Otherwise just do everything while it's in the chuck.

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                  • #10
                    Whatever you do, DON'T FORCE oversized material into collets.
                    A few of the geniuses I work with do that with drills, cramming them into the wrong collets.
                    The result is a nice assortment of SPRUNG collets.

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                    • #11
                      Hardinge makes 5c collets in .001 increments.

                      But I have used a tapered punch to slightly spring collets and never had a problem using them.

                      jimsehr

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                      • #12
                        What is a "sprung" collet? Won't it compress back down when you pull the drawbar?

                        Also, I have read various opinions on the internet. Some say you can go a little oversize vs the stamped size, some say you can only go undersize.

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                        • #13
                          Why not use "soft jaws" in/on a 3-jaw chuck - if done correctly is should be as accutate as (m)any collets.

                          Other than that use ER-32 collets (metric) which are in 1mm (0.04") steps with an effective gripping range of 1mm (0.04") in a size range of 2>20mm (0.08">0.20").

                          http://i200.photobucket.com/albums/a...rSmith01-1.jpg

                          http://i200.photobucket.com/albums/a...AirSmith03.jpg

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                          • #14
                            Many times I have used 5c collets with a 10 second cycle time in automatic lathes with air to open and close collets, no time to mess with stopping spindle and hand opening a collet. Lots of the time
                            collets have a spring in them to eject parts so you can reload new part without stopping spindle.

                            jimsehr

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                            • #15
                              Originally posted by beanbag View Post
                              What is a "sprung" collet? Won't it compress back down when you pull the drawbar?

                              Also, I have read various opinions on the internet. Some say you can go a little oversize vs the stamped size, some say you can only go undersize.
                              Complex issue---one I admittedly do not have the engineering background to address properly; however here is my understanding of the matter...

                              Depends on the way the collet is made. Not all collets are made the same regardless if they are all 5C or not. This is not a quality issue (although it surely could be). Some collets are made to collapse more to reach their nominal size when closed on the work. Some are made to collapse the fingers less. With those which open larger in the relaxed, open state, there is more of a leeway for oversize work. Up to a point.

                              Only at the condition where the collet is clamped on marked size is the bore ground into all the fingers parallel. The full depth of the bore is gripping the work evenly. For an oversize workpiece, the rear portion of the finger will contact the workpiece before the front while closing. As the collet is closed further, the fingers are distorted in being compressed into contact on the front portion. This has the potential to bend the finger---if it is bent past the yield point of the steel alloy used, the deformation becomes permanent. Likewise, undersize work contacts first at the front. The curvature bored into the fingers is not parallel and gripping the entire length of the seated work here either. The fingers can be bent past their yeild point here as well. As the rear part of the finger approaching the solid body of the collet is more supported, again the finger gets an unwanted curvature forced into it.

                              The overriding point to be made, though, is why use a collet at all? I can argue for two reasons: fine accuracy in workholding or convenience. Unless a collet is used with accurately sized work, there is no accuracy gained in using a collet! The fingers will contact the work over a limited distance because the collapsed bore in the collet is NOT parallel when it contacts the work. This lessens the security of the gripping force unless... The finger is further compressed to deform against the length of the bore and brought to grip the work its full inserted length. This, though, ruins the fine accuracy which the collet is designed to achieve. A scroll chuck is likely as accurate while providing a more firm grip on the work by which to drive it.

                              I fully understand that collets have other uses. This is what I was hinting at with my most-inexpensive-64ths-set previously mentioned. Sometimes you want to grip a short screw in the lathe to alter its length or turn down the head. I don't care if the mounting is super precise by any means. It is just more convenient and less distorting to the thread to grip in a collet. Soft jaws are great but less "fast" and convenient. Or maybe I have to hold something to use a wrench on it or file it or some other hand operation. I use a simple collet block gripped in the bench vise. Accuracy in concentricity, axial misalignment, repeatability---none of that matters to me in that instance. I would not expect, though, to use the same set of collets on work which does matter in those areas.

                              Hopefully something of the above is useful to you, and I don't come off as a pedantic obsessive Collets are an incredibly convenient and unobtrusive workholding device. You just have to pick your battles and balance the benfits to the consequences in a manner that suits your needs. Feel free to use all the oversize and undersize work you wish in your 5C collets. Just bear in mind, they may not perform up to expectation when they are absolutely required to if those boundaries are pushed far, often or without due caution.
                              Last edited by Arthur.Marks; 12-16-2012, 10:36 PM.

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