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  • collet question

    Does it make sense, if you have a lathe with an mt3 spindle, to get mt 3 collets? I don't have a mill. Seems like it would be the easy way to go.
    san jose, ca. usa

  • #2
    It may make sense depending on your need. There are points to keep in mind which may affect their use. 1) no through bore, so long part features or metal rod stock cannot be held. 2) They are available in limited sizes compared to other workholding collet types. The round, even stock sizes are easy to find in MT3 collet bores. Smaller graduations (i.e. 64ths or half mm's) or emergency blanks simply aren't available at all. 3) they take force to release from the taper after closing, but this concern has many solutions. The solution, though, will almost always require at least a small shop project to implement.

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    • #3
      I have the set of collets since I have a mini mill and mini lathe. The morse taper collets are supposed to be used on stock that is very close to the nominal size of the collet.

      I picked up an er32 collet chuck for my lathe ( two chucks in different styles, actually) and find that it's quite useful.

      One chuck mounts to the same mount as a 3 jaw chuck and has room to extend stock through the bore. The other has an MT3 shank that fits in the spindle and has a drawbar.

      Dan
      At the end of the project, there is a profound difference between spare parts and left over parts.

      Location: SF East Bay.

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      • #4
        it depends on what you want the collets for, in my opinion....

        IF you want them for holding stock, MT are a poor choice, for the reasons mentioned.

        However, as you mentioned not having a mill, you may be thinking of them as end mill holders, which is a much more practical idea. They do very well for single-ended end mills.

        it happens that I think weldon holders are nicer, partly because of the "reach" they give, but the collets would work also. I use MT2 in the vertical mill, and weldon for EMs in the horizontal spindle..

        The limited list of sizes for MT collets is no issue for end mills, as the shanks typically come in only a few common sizes.
        CNC machines only go through the motions

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        • #5
          ok thanks for the replys. usually I start a project with round stock, so I thought it would be easier to take stock out of the collet and replace it without dialing it in, like I do now with the four jaw. if 3mt is a bad choice, what do you guys recommend, keeping in mind working class newbie budget.
          san jose, ca. usa

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          • #6
            Littlemachineshop.com has ER32 collet chucks in both styles. You can also get ER40, which have larger collets.

            The collet chucks that mount inside the spindle via the 3MT taper are more likely to have less TIR, but the drawbar means that you can only fit about 3 inches of bar inside the chuck. The ones that are like a plainback chuck are still pretty accurate AND they allow the stock to stick through the headstock so you can easily make several small parts from a foot long bar.

            ER chucks are not real cheap, but the collets cover a large range of sizes and so a set of 12 or so will cover from 1/8 inch to 7/8 inch.

            Dan
            At the end of the project, there is a profound difference between spare parts and left over parts.

            Location: SF East Bay.

            Comment


            • #7
              Well, some may not like my suggestion..... but ...

              if you need a collet holder setup, they are not that hard to MAKE..... Seriously.

              The MT3 would take either 3C or 3AT collets, which are slightly different from each other but close in size. They cut the max stock diameter from about 7/8" to 1/2", but are available in a large number of sizes.

              You need 2 parts, with a possible 3rd. You need a collet adapter, a piece with an MT3 on the outside, and a straight section plus taper to fit the collet on the inside. A rim at the outer end to fit over the nose protector (see below) can be used to eject it, because they do get wedged-in

              Then you need a drawtube, a tube with a thread to fit the collet on the inside at one end, and a handwheel plus a flat bearing surface at the other, which is used to pull the collet in and close it on the workpiece.

              Optionally, you can make a "nose protector" that fits over the spindle nose, and in the case of threaded noses, can be used to eject the collet adapter. threaded on the inside to fit the nose, and has a hole to fit behind the rim of the collet adapter for ejection.

              Making your own tooling saves money (collet setups can run well over $100) and it provides useful projects for teh beginner.

              Is it a little "advanced" for some? Possibly.... but it;'s all normal stuff that will be routinely done, so no harm in "biting off a larger piece". Boring, turning, some threading, turning a taper, nothing too hard. (you use the compound to turn the taper).

              If you don't like the result, you are free to make a better one... and the result may be more accurately centered than a store-bought one.... it is made on and for your individual machine.
              CNC machines only go through the motions

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              • #8
                Originally posted by J Tiers View Post
                Well, some may not like my suggestion..... but ...

                if you need a collet holder setup, they are not that hard to MAKE..... Seriously.
                And along that line you can also make an ER chuck the same way. Machined to fit your spindle nose and mounted so final machining is done in situ it will be as accurate as you can get - at least to the limits of your machining and measuring ability.
                .
                "People will occasionally stumble over the truth, but most of the time they will pick themselves up and carry on" : Winston Churchill

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                • #9
                  JTiers, TGTool, thanks. I would rather make it than buy it. after all this is home shop machinist, any plans floating on the net?
                  san jose, ca. usa

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                  • #10
                    When I was doing batches of bushes from leaded EN1A on my Boxford, I used MT3 collets and a drawbar because I could grip very short lengths of material securely (well, enough for the particular job).

                    People often make far too much of chuck run-out. The way I was taught you plan your job so all concentric features are machined at one setting.
                    Paul Compton
                    www.morini-mania.co.uk
                    http://www.youtube.com/user/EVguru

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                    • #11
                      Just for the heck of it I built ER32 "collet block" from aluminum. That's not a great idea since the collets are spring steel and will scratch the tapered surface of the collet chuck. It was, however, quite usable. I made it on my 7x12 lather and it took no special tools.

                      The collet block was to allow me to hold small rods for work on my mill. They make 5C collet blocks with 4 and 6 sides to accurately index your cuts, and that was my inspiration.

                      Dan
                      At the end of the project, there is a profound difference between spare parts and left over parts.

                      Location: SF East Bay.

                      Comment


                      • #12
                        "Plans" are very simple...... The sizes of collets are listed all over, I think the OWWM site (it has changed names but there is a link forward) has most of the dimensions of a large number of collets....

                        So the outside of the adapter is the taper of the spindle, made long enough to fit nicely (and not run you out of compound travel) but leave the threads clear on teh collet. Inside is a hair bigger than the collet so it slips in, with the closing taper at the nose. The "rim" made to suit.... sufficiently bigger than MT3 to leave enough material in the adpater part, and large enough to fit over the "ejector/nose protector".

                        Drawtube.... large enough I.D. not to obstruct the largest rod diameter the collet takes.... O.D. small enough to fit in spindle (probably 0.75 inch for MT3) long enough to screw onto the collet and leave enough at the end of the spindle to take a handwheel and a couple washers to lower friction (or a thrust bearing if you want).

                        Set the handwheel with the tube screwed about halfway onto a collet, and the collet solidly set in place in adapter. That should leave enough to tighten.

                        Plans are hard because lathe spindles differ, and many dimensions other than the collet itself will vary between machines.
                        CNC machines only go through the motions

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