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switching between a 3 and 4 jaw chuck on a Rotary table?

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  • #16
    Sounds good, I am suspecting that an independant chuck will have more holding power bc of the direct pin gear. I work with delrin alot and altho it cuts like soap it's slippery as a fish. The more I think about it what I need is a 2 jaw chuck - aka a vise mounted on my Rotab. Wish I'd thought of that sooner it really is all I need!

    Originally posted by Toolguy View Post
    What works for me is an 8" 4 jaw scroll chuck on an 8" Vertex H/V rotary table. The 4 jaw holds round and square very securely. The rotab has 4 T slots and the chuck has 4, 1/2" grade 8 bolts, 1 next to each jaw, holding T nuts. The rotab was set up on the mill, dialed in for center, the chuck put on, T nuts lightly tightened, chuck dialed in, and cinched down. I've been using this setup for years and never needed to change it. I have used it in horizontal and vertical mode many times each.

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    • #17
      If you have some soft jaws, they can be bored to the size of the delrin and will hold better and more accurately. That would work with vise jaws as well as chuck ones. As long as the vise could be positioned on the RT centreline. If the delrin you are working with is 26mm diameter or less, then you could hold it in an er40 collet plate which would be easy to fit to the RT.
      Last edited by old mart; 05-05-2021, 09:56 AM.

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      • #18
        Old Mart, I'm gonna go look around for types of soft jaws. I was looking for machinable jaws last week. I need to machine "V" notches in some jaws to hold round stock vertical and horiz. Do you know what soft jaws tend to made from? I guess soft steel and alum. I have brass jaws in my workbench vise that I like.

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        • #19
          Originally posted by Mcgyver View Post
          What ever lathe spindle mount you have, cam, threaded, whatever.....make an exact duplicate of that that catches the centre register of the RT and bolts to the RT. Then any tooling you use on the lathe can be used on the RT, without even removing the work if you like.
          ...now, THAT's an idea I may just steal!

          t
          rusting in Seattle

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          • #20
            A long time ago I put a four jaw on my little eight and a half by 18 lathe. When I needed to do quick repeat work with a three jaw I just took a smaller one and put it in the jaws of the four jaw and clocked it in.

            There may have been an issue with overhang but I don't remember it being an issue. On something like a rotab it shouldn't be an issue at all if you have enough vertical clearance.
            *** I always wanted a welding stinger that looked like the north end of a south bound chicken. Often my welds look like somebody pointed the wrong end of a chicken at the joint and squeezed until something came out. Might as well look the part.

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            • #21
              I have a RT with an MT center hole. I though it would be simple to get a matching MT center and mount my fixture to it for automatic centering, but the MT center projects quite a long way out of the hole, which would leave the work wobbling up in the air as it were. Yes, the taper is the same MT for both the hole and the center, but it's certainly not "plug and play". More like "some assembly required".
              "A machinist's (WHAP!) best friend (WHAP! WHAP!) is his hammer. (WHAP!)" - Fred Tanner, foreman, Lunenburg Foundry and Engineering machine shop, circa 1979

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              • #22
                I only use the MT in the centre of the RT to get the chuck concentric prior to bolting it down. With a 3 jaw scroll, gently close the jaws on the MT arbor. You could use a MT with a soft arbor for this and have a thread in the end to help to remove it after the chuck is secure. The alignment of a 4 jaw independent is not important when securing it to the table, I just hold it as near as possible with my fingers.
                Last edited by old mart; 05-16-2021, 11:39 AM.

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                • #23
                  Originally posted by Bill White View Post
                  I have my grandfathers 5" Cushman 3 jaw from about 1900, the scroll nuts are proud of the body- a real knuckle killer (old old old). Funny thing is he was a trained MIT engineer and this OLD lathe was his first machine tool, he ended up with 50 employees making springs for like 75 years. I think thats why he set it aside for 65 years before I ever saw it. It's perfect, like it never did a days work.

                  Perfect for me anyway! I dont do much of a days work either!



                  An old chuck in good shape with the scroll nuts poking out is the perfect candidate for a rotary table. As for mounting, what I've found that works well is pulling the back plate off and substituting an intermediary plate made from about 1/2" thick aluminum. Bolt the plate to the chuck using whatever centering method that's convenient, then putting the plate plus chuck onto the rotary table using whatever alignment works best. For aligning plate to chuck I've used things like a pin of appropriate diameter(s) at the center of rotation, or having small dowel pins located near the outside diameter of the chuck. The dowel pin method works great when there is need to maintain some sort of clocking accuracy along with the concentricity.

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