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Holding rough stock in collets

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  • Holding rough stock in collets

    How susceptible to damage are collets (ER) when used to hold stock that is rough, ie: slightly out of round, rusty etc? I always use the 3 jaw for initial turning of rougher stock but it would be nice not to have to change out the chuck.

  • #2
    Simple answer: never run rough stock in precision collets, rust and scale wears the precision ground bores and the irregularity may spring if it's closed tightly.

    If chuck changes are a chore consider storing your chucks handy to the the spindle and rigging a simple aid that lifts and transports the chuck from storage to installation position. Clean, safe 20 second chuck changes are possible if you're organized and the chucks are small.

    You really shouldn't run rough stock in a three jaw either.
    Last edited by Forrest Addy; 02-19-2013, 06:58 AM.

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    • #3
      If your range of collet sizes allows, you could use a copper or aluminum sleeve between the collet and the shaft. That will give you some degree of protection for the collet, but you do still risk deforming, or springing it. I don't like to put rough stock in my 3 jaw either. I'll often take the workpiece to the drum sander and rotate it while in contact with the drum to remove much of the irregular surface- then put it in the chuck. The sanding helps to show whether it's out of round also- you need to develop a feel for this. If it's not round, it shouldn't go in a collet.
      I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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      • #4
        Not only is there a wear issue, but collets are intended for holding stock very close to correct size, and ideally AT correct size.

        The ER collets have a considerably wider range per size, so the "correct size" has more variability accepted than with a 5C, for example, but then also they are potentially easier to deform, with all the splits in them. You really want to use good round standardized stock in any collets.

        Out-of-round stock will cause an ER collet to grip with some sections and have others loose.... the stock may not be securely held, and the collet may get side forces that twist and bend the few sections that are actually gripping . They are intended to carry those forces with ALL the sections.

        And, of course, no dirty as-cast / as-rolled stock, for the reasons Forrest mentioned.
        1601

        Keep eye on ball.
        Hashim Khan

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        • #5
          Considering I can find a full, by 1/8" (to take an example) ER32 set for <$70 shipped, I would go that route and not worry about it. I know we like to prize our collets, and it is wise to do so for holding precision work with quality collets. Still, they are considered consumables. Besides, how accurate do you really need them to be on rough stock that may not be precisely round, on size, perfectly straight, etc. to begin with? I would bet the collets hold up very well as long as the stock extends through the full gripping length of the collet fingers. Given the convenience, low cost per collet, I see no reason not to use them. Just keep a cheap set for rough stock and don't expect them to be stellar precision when such is needed.

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          • #6
            Originally posted by Forrest Addy View Post
            Simple answer: never run rough stock in precision collets, rust and scale wears the precision ground bores and the irregularity may spring if it's closed tightly.
            I've seen the Hardinge serrated 5C collets that are meant for hot roll, but I've always wondered how they deal with the diameter variation? Seems so much easier to just take a skim cut...
            "Twenty years from now you will be more disappointed by the things that you didn't do than by the ones you did."

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            • #7
              Originally posted by Arthur.Marks View Post
              Considering I can find a full, by 1/8" (to take an example) ER32 set for <$70 shipped, I would go that route and not worry about it. I know we like to prize our collets, and it is wise to do so for holding precision work with quality collets. Still, they are considered consumables. Besides, how accurate do you really need them to be on rough stock that may not be precisely round, on size, perfectly straight, etc. to begin with? I would bet the collets hold up very well as long as the stock extends through the full gripping length of the collet fingers. Given the convenience, low cost per collet, I see no reason not to use them. Just keep a cheap set for rough stock and don't expect them to be stellar precision when such is needed.
              Yes, but what you don't take into consideration is the scale and rust coming off, going thru the slots, and damaging
              your nicely presice hardened and ground spindle (the part where the collet fit's into)

              Every cycle of open and close grinds that crap into the spindle taper.

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              • #8
                Originally posted by digger_doug View Post
                Yes, but what you don't take into consideration is the scale and rust coming off..............

                Every cycle of open and close grinds that crap into the spindle taper.

                Boy Howdy! That gives me the chills!!


                Rex

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                • #9
                  Jeez, man, how rough is this stock?! Might run a cloth of wire mesh down the stock before loading? I wasn't picturing a full-on production bar feed run of the stuff.

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                  • #10
                    About as rough as cold rolled with a little surface rust, brushed or sanded smooth, I was looking for a single work holding solution for anything up to 1" (er40). I guess there is no free lunch. Another justification for a second lathe!

                    As far as 20 second chuck changes, it's not just the 3 jaw, it's re/re the collet chuck with a drawbar as well. A screw-on ER chuck would simplify the procedure.

                    I never thought of the consumable approach, reserving a cheap set of collets for the rough stuff is viable.

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                    • #11
                      Originally posted by martik View Post
                      I never thought of the consumable approach, reserving a cheap set of collets for the rough stuff is viable.
                      Yeah, just like having a "rough work" chuck..... When you said rough stock, I, at least, envisioned worse..... you didn't actually say that, though.
                      1601

                      Keep eye on ball.
                      Hashim Khan

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                      • #12
                        The idea of using ER collets for stock holding seems to have come from the HSM community as a way of covering wide diameter ranges with a minimum collection of collets. AFAIK, ER's were originally intended only for tool shank holding where it's a given the shank will be round, smooth and straight. So, if your part is not round, smooth and straight, it may not be wise to use an ER.

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                        • #13
                          Originally posted by lazlo View Post
                          I've seen the Hardinge serrated 5C collets that are meant for hot roll, but I've always wondered how they deal with the diameter variation? Seems so much easier to just take a skim cut...
                          In my experience serrated collets are used where a smooth bore collet doesn't give the needed grip. An example would be trying to form tap 1/2 13 in 3/4" 304 SS. A smooth collet has trouble holding that.

                          Serrated collets are expensive. You can ruin one in an instant if the part spins at all in the collet. That can happen using under size or rough material that doesn't have full contact. The serrations are sharp, when the part slips or spins material scrapes off the part and for practical purposes welds into the serrations, essentially you then have a smooth bore collet (with a not so smooth bore).

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                          • #14
                            Originally posted by Forrest Addy View Post
                            Simple answer: never run rough stock in precision collets, rust and scale wears the precision ground bores and the irregularity may spring if it's closed tightly.

                            If chuck changes are a chore consider storing your chucks handy to the the spindle and rigging a simple aid that lifts and transports the chuck from storage to installation position. Clean, safe 20 second chuck changes are possible if you're organized and the chucks are small.

                            You really shouldn't run rough stock in a three jaw either.
                            Forrest - does that advice also apply to the Jacobs Rubberflex or Pratt-Burnerd collets?
                            Mike Henry near Chicago

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                            • #15
                              Why would you want to hold rough stock in a collet???

                              Collets are used to hold finished sizes mostly for second operation work or new work on good finished /ground material. You would gain nothing by using a collet over a chuck for rough finished/rusty material..
                              The shortest distance between two points is a circle of infinite diameter.

                              Bluewater Model Engineering Society at https://sites.google.com/site/bluewatermes/

                              Southwestern Ontario. Canada

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