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  • Work pics - expanding pneumatic collet

    Just thought I'd share some pics from my current work project. Most stuff I do isn't very interesting but this project was kinda cool so I thought I'd share. All the pics are in the order of operations.

    Used the CNC mill to pre-rough out the collet. OD is 4"x5" long 4140-ph. Used the mill because we don't have a suitable chuck for the CNC lathe so the mill did the donkey work for me. Attacked from both sides because of tool reach.


    I love the SECO high feed end mills we have. They really make good use of HAAS power and light work of what used to be annoying steel jobs. I left 0.07" on here just in case.

    While the mill was chugging away I made the pull down rod and endcap you will see later.

    Boring the collet ID and the dual 20* tapers, with my shop made boring bar from last week. Worked great. Also faced and skimmed the od to flip around and do the other side.....

  • #2
    First op on the arbor is boring out the back side for the air cylinder, facing the bottom, and finishing the od @3" for a light press fit into the base plate.
    My weapons of choice. Drilling the start hole was the worst part of this hole build.



    done op1, flip it around for op2. Dialed in ~0.001" TIR along the length. I'd rather be lucky than good .

    I cut the male tapers with the same compound setting as the collet and used the boring bar on the back side and run in reverse. I was going to flip the compound but the boring bar cut better than expected and the large taper blued out pretty good against the collet so I just ran with it.


    I then had to "time" the tapers so they matched the ones already cut in the collet. Because the large taper contacted first I had to drop it 0.063" until both tapers contacted at the same time. My plan was to take 0.010" off the big one until the smaller one contacted then recut the small one in 0.001" increments until they both contacted but I got 3 passes in with no contact before I started wondering just how far off I really was lol. So after some head scratching on how to measure it easily I melted some cutter wax onto the small taper and slid the collet on again until it bottomed out, then measured the squished wax thickness. Some quick math and I had a number to get me in the ball park. A couple more passes and I had both tapers blueing out pretty good. Didn't take any pics of that because it was late (8:30) at work, I was tired, and I had prussian blue all over my hands and didn't want to get it on my phone. The black sharpie picture was the first trial, but I switched to prussian blue after that. I get away with using sharpie for a lot of stuff I do but it wasn't cutting it here. Never fails though, everytime I get out the blue I get it all over everything lol.

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    • #3
      Next up I slid the collet on the arbor, and held it in place with the end cap I already made prior to all this. There was a sequence of things I had to make just so I could hold the next thing without having to break setup. All was going to plan until I realized that in my excitement to start eh mandrel I forgot to face the other sawcut end of the collet before this step..... the sawcut end was too out of square to drive with the endcap/center so I had to toss it in the mill to face it off square as I didn't want to disturb the arbor from the setup I cut the tapers in. Minor hiccup, but all went well and I finished the OD at 3.66". I love turning hard steel, so shiny.


      I thought about cutting the finished OD in the expanded position after I cut the slots but for the end purpose of this it will be fine. It's a welding fixture and will not be an issue. After cutting the od and removing the mandrel I chucked up the collet again to face it to length at 5".

      This morning was a little nerve racking drilling and cutting into the collet but it needed to be done.
      Layed out the holed and slots in cad and printed out a guide. The circumference was longer than a sheet of A4 paper and I didn't feel like walking to the front of the shop to use the plotter so I just rotated it until the important parts fit on a sheet and taped it on. Note the missing corners.

      Drilling the last hole

      Cutting the first slot

      Made a quick cradle to hold the collet for drilling and slot cutting out of a chunk of scrap.

      LAST slot. What a nerve racking process. Had 2 slots that despite my best efforts of fixturing and securing everything drifted a bit. They stick out like a sore thumb to me, but don't effect the operation of the collet so they get to stay....


      I used the roll in saw instead of a slitting saw, simply because I didn't have a suitable one (common theme of this job...). I would have rather done it in the mill as it would have came out nicer, but sometimes one needs to keep in mind the context of the job, and simply use what they have available. Bandsawn slots were were more than acceptable here.

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      • #4
        After cutting the last slot I did a quick deburr (still need the od done), and finished the endcap, and pull down rod that screws on the cylinder.
        I was running short on time as I had to leave at 4:30 to coach the kids baseball and start a short holiday, so I won't be back till Monday. But I just HAD to throw it together to test it out and ease my mind that it would work before leaving. Pretty rough assembly and a few things still need to be done but IT WORKS. So relieved. Then I had to tear it back down to send the arbor out for hardening. The travel is limited based on the gap between the end of the arbor and a shoulder cut on the endcap.


        https://i.imgur.com/6bcSF3cl.mp4

        I pretty much just shot from the hip on most of this job, and designed things around what we had as I went. Everything seemed just a bit too big to fit our equipment or my normal methods of processing. It was challenging to say the least.

        Now I'm in holiday mode. Have to get up early and drive a couple hours to my Sisters cottage for some much needed family vacation and fishing time. .

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        • #5
          Nicely done, Dan. I make these fairly commonly and have come to really appreciate the WEDM for them. But, there are times that the machine is busy making parts, and just like you have discovered - the collets just do not actually care. They work just fine. However, I do share your aversion to the sharp stick in the eye of the occasional wandering cut. Just grates on me... Haha. Again, nice work.

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          • #6
            Originally posted by Zahnrad Kopf View Post
            Nicely done, Dan. I make these fairly commonly and have come to really appreciate the WEDM for them. But, there are times that the machine is busy making parts, and just like you have discovered - the collets just do not actually care. They work just fine. However, I do share your aversion to the sharp stick in the eye of the occasional wandering cut. Just grates on me... Haha. Again, nice work.
            Thanks Zahnrad. WEDM would be nice for a lot of things that we do, but we just don't have enough work for it to justify one. We've got 2 customers that send us big gauge packages about every 2 years that require a lot of outsourced WEDM stuff, but in between that it wouldn't get run enough. Same problem we have with the CNC lathe, the work for it comes in waves. The lathe is fine to sit for a couple months of sporadic use, but I don't think a wire machine would like that.

            I think the wandering cut would bug me more if I had to look at it everyday, but this will be leaving here shortly to hopefully never be seen again lol.

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            • #7
              Nicely done. I thought I was the only one that used paper templates on a part I was making. It sure helps to visualize things.

              JL............

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              • #8
                Originally posted by JoeLee View Post
                Nicely done. I thought I was the only one that used paper templates on a part I was making. It sure helps to visualize things.

                JL............
                Thanks Joe. Paper templates are surprisingly accurate for quick and dirty stuff like this that only gets checked with an eyecrometer.

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                • #9
                  Thanks, interesting project.
                  Your band saw is still high tech solution for slotting compared to my hand-held angle grinder and thin 1mm disk
                  Location: Helsinki, Finland, Europe

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                  • #10
                    Originally posted by MattiJ View Post
                    Thanks, interesting project.
                    Your band saw is still high tech solution for slotting compared to my hand-held angle grinder and thin 1mm disk
                    I briefly thought about using a zip disk in an arbor on the mill, but decided against it. .

                    here it is all finished up, painted and ready to ship.




                    link to video
                    https://imgur.com/xe8xftN

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                    • #11
                      Call it intuition, but I had a feeling right from the start that this thing was going to come back for a resizing of the collet (make it to part print vs make it to part/process)..... That thought drove the design right from the start. Yesterday it came back and I had to remove 0.3" from the od of the collet....

                      I turned a spacer ring that fit between the chuck and collet so that I could preload the collet on the tapers about 0.01". That carbide tool was switched before machining for a 3/4" HSS tool, and I had to play around with the grind a bit to find it's happy place (there was no happy place). Material is 4140ph and is a giant spring essentially. I could only do about 0.02" per pass and every 3-5 passes I had to stop and remove/clean everything because chips would vibrate down through the slots and cause the whole thing to go out of round. About half way through roughing it I had a lightbulb moment and robbed a hose clamp from the dust collector on the surface grinder. Clamping the od and roughing it in halfs went much better, but still sucked.

                      Here it is after a quick polish with emery and scotchbright.

                      And here it is actually able to hold the part now...

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                      • #12
                        Very nicely done project! Better too big than too small.
                        Kansas City area

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                        • #13
                          Dan,

                          I like to hot glue the slots and holes when remachining is necessary. It can be pushed into any cavity, serves very nicely, and is easily removed when done.

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                          • #14
                            Nicely done. Yeah I'll bet that it would have been a tricky operation, much like trying to turn a tuning fork.
                            Somewhat like trying to turn a brake drum without the strap to quell vibrations, glad the hose clamp worked. Wonder how a few strong rubber bands would have worked?

                            Zahnrad, I like the hot glue idea, I'll have to remember that one.
                            Home, down in the valley behind the Red Angus
                            Bad Decisions Make Good Stories​

                            Location: British Columbia

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                            • #15
                              Impressive work, and very nicely documented. I thought cutting the slots on the bandsaw was kind of clever since you could cut 2 slots at once.

                              Looks like part of a big ass rheostat mounted on there:
                              Originally posted by Dan Dubeau View Post
                              And here it is actually able to hold the part now...
                              Location: Long Island, N.Y.

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