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The vageries of import collets

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  • The vageries of import collets

    So, I have a useful assortment of 5c collets. Quite a few that I've never tried. My 15/16 is one in the never used department. I discovered that it would not accept a .937" dia. workpiece. A quick and dirty measurement with the dial calipers showed the diameter at .935. Well now, this a fine kettle of fish! I wanted to insert some kinda delicate aluminum parts, and I didn't want to scratch them up.


    What would you do? I decided to try to expand it a little. No go. Snap it went. Oh well, garbage in, garbage out. My advice is to qualify anything that comes into your shop. Tooling cutting tools raw stock etc. it's what I did when I was a heavy duty truck mechanic. Parts weren't always acceptable. I've been retired a while now, how soon we (me) forget..... Click image for larger version

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    I cut it off twice; it's still too short
    Oregon, USA

  • #2
    Hate to say it but .002" is not something that will be a deterrent in installing a part into an expandable collet, in fact it's the norm in allot of circumstances, I routinely install drill bits or material that's .010" over or undersize without a problem (in my R8's)

    what you can't do is try to expand the collet way past and expect it to deform --- they are super hard and will break as you found out, and 15/16ths are getting very thinwall towards your threaded area (as you found out) this really is "user error" more than poor collets...

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    • #3
      Boomer, I wholeheartedly agree. It's owner abuse. However, the " name brand " collets I have here have clearance for the nominal diameter. A typical example is a 1" size Hardinge I have here. The free diameter is roughly 1.009". Others such as enco, royal and Neal Skokie show clearance also.
      I cut it off twice; it's still too short
      Oregon, USA

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      • #4
        Well, if I was hard pressed enough, I'd take a feeler gauge, jam the appropriate thickness shim in the slits, take out my tool post grinder, put on the internal stone, and grind it .0025 larger.

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        • #5
          In all likelihood, the original 15/16 collet was made with the correct radius on each leaf of the collet. It just sprung closed a little during heat treat.
          Good collet makers have figured out how to make them always spring open not closed.

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          • #6
            I have an intermediate set - kinda a mixed bag as some are actually very close to the size that it's rated at and some are definitely a little bigger - none are smaller that I know of - maybe a couple thou but don't really notice it --- I will concur that using my buddies hardinge collets they all seem to have some clearance - I think allot of this is simply due to them being used with chucker machines and you want the parts to fall out when you un-chuck,,, really not needed in my R-8's and I can't think of a couple thou really effecting stopped static hand insertion at all as the collet is sliced and will open that amount very easy,

            sometimes when installing an endmill I find I need to push down on the drawbar to keep the collet from contacting its taper - because if that happens it will not allow the tool to go in, don't know what set up your 5-C's using for cinch down but if it's not keeping the collet away from the taper the same thing could be happening to you, then push all you want it's only going to shut it out more...

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            • #7
              Some time ago I bought a big set of 5C collets, chineseium. And I wanted a one really good 3/4" collet, thus I purchased a more expensive 3/4" collet.
              Damn if the expensive one has more runout than the cheap one!!

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              • #8
                Next time you spread one, heat the area at the base of the slits. A collet doesn't need to be hard there anyway.

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                • #9
                  Funny timing. I cracked an import 16-17 er 32 collet today trying to clamp down on a 3/4" reamer shank (0.625/15.875). Didn't have another free 5/8" collet available without tearing apart other setups, so I gambled and lost. That extra 5 thou broke the camels back. Ended up having to shuffle some tools around to free up a 5/8" collet anyway just to ream 6 holes. I doubt that collet has ever been used in over 10 years, so the only loss was the time spent trying. Even though they're supposed to have a 1mm/0.04" clamping range I find the best results from using size on collets for gripping.

                  Our 5c collets in gen pop at work are all kinds of sprung and messed up, but I've never seen one crack like that. All the import stuff I've dealt with has always been super hard and brittle. Makes you wonder if a tempering cycle would make some of this import tooling a little bit more resilient while sacrificing some longevity. For some tooling it might be worth it.

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                  • #10
                    .002" should not stop you from tool or material installation - again if it does your probably pushing the collet against it's taper and closing it with the material your trying to install - another thing is to make sure it does have a mild chamfer on the insertion part of the ID,,,

                    but - if he's doing hundreds of parts in a chucker type situation .002" is enough to screw the whole procedure up as it will not let go of the last part,,, then something has to be attempted - perhaps taking a stab at heating it where you said with something oversize already inserted...

                    keep in mind TIm, this is all hindsight 20/20 stuff, we all push things to the limit and it's easy to speculate after that "pop" sound,,,

                    i have a 5/16ths endmill story I can tell you about that happened just last week lol
                    Last edited by A.K. Boomer; 02-11-2020, 11:43 PM.

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                    • #11
                      They probably bored or reamed it out to size and then the heat treatment shrunk it a bit.

                      Perhaps it may have been better to put a chamfer on the entrance hole (Dremel work). And de-burr the edges of the slots with a triangular stone. That way a part could be inserted into it without scratching it a lot. After a few parts the collet would probably have expanded a bit on it's own.
                      Paul A.
                      SE Texas

                      Make it fit.
                      You can't win and there is a penalty for trying!

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                      • #12
                        The splitting is common with cheap imports. But if you're stuck with crap you have no choice other than trying to open them up since they're un-usable sprung closed.

                        We spread Hardinge collets all the time using a screw driver pounded in the slots when somebody accidentally power closes one with no material in it.

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                        • #13
                          Originally posted by DR View Post
                          We spread Hardinge collets all the time using a screw driver pounded in the slots when somebody accidentally power closes one with no material in it.

                          Wow --- that's brutal and being forced both directions and they still hold up, Tim's correct then - it is more of a cheap problem, maybe hardinge anneals their collets close to the shank end for flexibility/durability

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                          • #14
                            Originally posted by A.K. Boomer View Post
                            Hate to say it but .002" is not something that will be a deterrent in installing a part into an expandable collet, in fact it's the norm in allot of circumstances, I routinely install drill bits or material that's .010" over or undersize without a problem (in my R8's)

                            what you can't do is try to expand the collet way past and expect it to deform --- they are super hard and will break as you found out, and 15/16ths are getting very thinwall towards your threaded area (as you found out) this really is "user error" more than poor collets...
                            I agree. I think 5C gripping range is
                            + - .003 either side of the size.
                            Just out of curiosity, what brand are the collets?

                            JL....
                            Last edited by JoeLee; 02-13-2020, 09:44 AM.

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                            • #15
                              why would it make a difference which way you try to spring the collet?

                              .002" on a 15/16" collet is on the order of simply.. touching it with a finger.

                              maybe chuck them in an oven at 500F for 3 hours.

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