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what are collets used for on a mill?

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  • what are collets used for on a mill?

    i understand the use of collets on a lathe (and in fact have used them), but on a milling machine are they just used to hold endmills and twist drills? is there any reason a collet is any better than a quality, tight-fitting endmill holder?

    i got that UP mill/drill up and running and bought a few endmill holders to fit the common endmill shank sizes. i was looking at collets (it takes the R8 variety), and then got to thinking, if my endmills all fit in the endmill holders, and i have a decent drill chuck, just what would i use the collets for? i can't see any reason to hold round stock in one on a mill.

    thanks for any insight (and excuse to spend my money).

    andy b.
    The danger is not that computers will come to think like men - but that men will come to think like computers. - some guy on another forum not dedicated to machining

  • #2
    Read LittleMachineShop's Mill tooling page. It tells

    an end mill holder will always be at least a little bit off and if the shank is undersize it will be off by that much. By contrast a collet is good for whatever it is ground to, and what it's collapse is. This could be good for odd or home-made tooling that may not be precise. Also a collet gives a posssible safety valve by slipping, not so a holder with set screw. It can be faster to change, can use a power draw bar, and can give you more Z room, also is generally cheaper.
    That sounds biased but it is just the one side. Provided you have z room holders have many advantages.

    Also collets are good for tiny sizes (good luck with a 1/16 set screw)

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    • #3
      Well, using a collet saves on real estate in the Z axis. Keeps the tool closer to the spindle which I assume makes for a more rigid set up, and gives you more working room between the tool and the table.
      (Of course I'm a total amateur, FWIW....)

      What would you use a collet for? How about holding a test indicator for tramming the table, locating features on a part, centering holes, etc., or holding a center or edge finder....

      I'm sure others here can give you many more examples.

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      • #4
        The mill drill can use all the stiffness it can get. In this case, the collet reduces the overhang of the tool and in the process, reduces the deflection of the tool. I used only collets in my M/D and am using collets now in a knee mill except for shanks larger than the "standard" R8 max.

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        • #5
          Originally posted by nheng
          The mill drill can use all the stiffness it can get. In this case, the collet reduces the overhang of the tool and in the process, reduces the deflection of the tool. I used only collets in my M/D and am using collets now in a knee mill except for shanks larger than the "standard" R8 max.

          That's a good point. I use both but I actually prefer the collets.

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          • #6
            Originally posted by nheng
            The mill drill can use all the stiffness it can get. In this case, the collet reduces the overhang of the tool and in the process, reduces the deflection of the tool.
            That's true on any mill short of a Cincinnati or a Kearney & Trecker

            That's the downside to the ER chucks too -- they're incredibly convenient, but they increase the spindle overhang almost as much as an endmill holder. So I use collets up to 3/4", and endmill holders for the rare cutter that's bigger.

            Andy_B: if you buy a cheap set of collets, check them right away for runout and the fit in your spindle. Some of the Chinese collets (and endmill holders) are really bad, but a good dealer like Enco will send you a replacement set at no charge, so you can pick and chose the "good" collets, and send the rest back.
            Last edited by lazlo; 10-10-2008, 10:39 AM.
            "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
              I would never dream of using a chuck on a mill I would even use collets on mty drill if I could. As said less overhang and also much better holding power truer cutting etc that's what I find.How many people see a drill chuck with their eyes just wanderring a very tiny amount collets collets colets whenever possible excuse typing love you guys Alistair
              Please excuse my typing as I have a form of parkinsons disease

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              • #8
                Alistair, an ER collet chuck is just an R8 adapter on one end, and a ER-40 quick-change collet chuck on the business end. It's made for a milling machine. But it does have about an inch and a half of overhang -- less than an endmill holder, but you still notice the difference in rigidity.

                One of these days, I want to send a Bridgeport 30 Taper spindle (which are cheap as dirt on Ebay, 'cause no one wants them ) to Wells-Index and have them regrind it for ER-40. That would be sweet...
                "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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                • #9
                  Originally posted by lazlo
                  Alistair, an ER collet chuck is just an R8 adapter on one end, and a ER-40 quick-change collet chuck on the business end. It's made for a milling machine. But it does have about an inch and a half of overhang -- less than an endmill holder, but you still notice the difference in rigidity.

                  One of these days, I want to send a Bridgeport 30 Taper spindle (which are cheap as dirt on Ebay, 'cause no one wants them ) to Wells-Index and have them regrind it for ER-40. That would be sweet...
                  Why you would just create more problems. the rest of the machine is not rigid enough. For what a BP are clone was designed for it does a great job. If you want a solid machine buy a Cincinnati , Brown & Sharp , Kernet trucker are any outer heavy duty mill with a 40 are 50 taper spindle.
                  Every Mans Work Is A Portrait of Him Self
                  http://sites.google.com/site/machinistsite/TWO-BUDDIES
                  http://s178.photobucket.com/user/lan...?sort=3&page=1

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                  • #10
                    so if you use a collet to hold endmills, must you use single-ended endmills? i have a few double-ended ones and i was afraid all they would do was machine out the ID of the collet.

                    i did go check the mill and you're right about getting more z-height with a collet. i'll take your word on rigidity since i don't have any collets to check at present.

                    andy b.
                    The danger is not that computers will come to think like men - but that men will come to think like computers. - some guy on another forum not dedicated to machining

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                    • #11
                      Originally posted by lane
                      Why you would just create more problems. the rest of the machine is not rigid enough.
                      Not for rigidity Lane -- for the convenience. Having a quick-change ER spindle chuck is a wonderful convenience. I can change tools as fast as a power drawbar. The only downside is that the ER collet chucks increase the spindle length by about an inch and a half.

                      ER-32 and R8 have nearly identical dimensions, so you could easily have Wells-Index regrind an R8 spindle for ER-32, but I've tooled my mill, lathe and T&C grinder for ER-40, which would need a bigger spindle nose for a re-grind -- which is why I'd start with one of the Bridgeport 30 Taper spindles.
                      "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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                      • #12
                        Ill bet many collets are just as far "out" as the end mill holders.......

                        My Bison brand EM holders release the EM with a "pop", and I have to hold the EM in for a bit when installing to let the air leak out...... not much "off" in the fit, at least.

                        Check the specs on collets. Many are specd to be within 5 tenths or so, not bad, but not perfect.
                        1601

                        Keep eye on ball.
                        Hashim Khan

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                        • #13
                          Having a ER native spindle would suck. You could only use and mills and drills or shanked tooling. Cincinnati and others made mills with their own styles of collets similar to ER. (Double angle collets)

                          I changed my spindle to 30 Taper from R8. So much nicer now. I have collet chucks that I can pop into place and the offset stays so I know where the tool length stands between ops.

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                          • #14
                            Originally posted by J Tiers
                            Ill bet many collets are just as far "out" as the end mill holders...
                            Not concentricity Jerry -- overhang. A collet has zero overhang. An endmill holder sticks out the end of the spindle by 1 - 3 inches, so it's a lever-arm on the spindle, and you lose some rigidity.

                            Same deal with my R8->ER collet chuck.
                            "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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                            • #15
                              Originally posted by macona
                              Having a ER native spindle would suck. You could only use and mills and drills or shanked tooling.

                              Cincinnati and others made mills with their own styles of collets similar to ER.
                              I don't follow Jerry -- do you mean that you couldn't use native R8 tooling? That's true, and that's why no one wants the 30 Taper spindles for the Bridgeport -- then you can't use all the cool Bridgeport accessories: the Voltro rotary heads and multi-angle attachments, the right angle attachment, the horizontal milling attachment, the Quillmaster multi-angle attachment and the QRA (dental drill) attachment...

                              I changed my spindle to 30 Taper from R8. So much nicer now. I have collet chucks that I can pop into place and the offset stays so I know where the tool length stands between ops.
                              That's the only advantage I can see to 30 taper on a Bridgeport -- the constant offset. You have a CNC Bridgeport, rigtht? The Bridgeport itself is a relatively small, 1.5 horsepower machine, so the R8 spindle isn't a limiting factor, in my experience.
                              "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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