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How does one mill a 60" radius without a really huge rotary table?

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  • How does one mill a 60" radius without a really huge rotary table?

    A small amateur observatory needs a SS part that is about 2" wide by 15" long and 1/2" thick, and needs to have a 60.00" concave radius milled on on side and a 62.00" convex radius milled on the other side (plus a few mounting holes).

    Any ideas on how to do this without CNC?

  • #2
    Originally posted by Dan_the_Chemist View Post
    A small amateur observatory needs a SS part that is about 2" wide by 15" long and 1/2" thick, and needs to have a 60.00" concave radius milled on on side and a 62.00" convex radius milled on the other side (plus a few mounting holes).

    Any ideas on how to do this without CNC?
    Smooth Arc function on the various Ditron(Chinese) DRO's can do this.

    Comment


    • #3
      remove z-axis feedscrew and jury-rig pivoting point that couples z-axis movement to x-axis.. or make some improvised friction loaded "auxiliary table" that turns around pivoting point and is driven by allthread..
      Location: Helsinki, Finland, Europe

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      • #4
        Originally posted by Dan_the_Chemist View Post
        A small amateur observatory needs a SS part that is about 2" wide by 15" long and 1/2" thick, and needs to have a 60.00" concave radius milled on on side and a 62.00" convex radius milled on the other side (plus a few mounting holes).

        Any ideas on how to do this without CNC?
        Sounds like a good part to have laser cut (or water jet)
        Location: Northern WI

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        • #5
          If your dro doesn't do it calculate the XY points at the resolution you need and manually step the dro. Going to suck on stainless..

          CNC makes this a breeze, but you know that. lol

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          • #6
            Easy without DrO.. will explain brief from ad more later. . Make a pivot if the mill like toolbox or table saw or bench.
            make a frame , can be wood, T square or hammer shape. Pivot on small end, work goes on fat end.
            this will swing your work through correct arc.. move work with a lever or in some cases acritary table with pin sliding in a slot, or a screw drive..
            it will work.

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            • #7
              Two milling machines. Then a welder JR
              My old yahoo group. Bridgeport Mill Group

              https://groups.yahoo.com/neo/groups/...port_mill/info

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              • #8
                Originally posted by Dan_the_Chemist View Post
                A small amateur observatory needs a SS part that is about 2" wide by 15" long and 1/2" thick, and needs to have a 60.00" concave radius milled on on side and a 62.00" convex radius milled on the other side (plus a few mounting holes). Any ideas on how to do this without CNC?
                There are several ways to tackle this and some depend on the length of the material.
                Say if it is 20" , you can drill holes near both ends to help control the work piece.
                But I want you to think about this ...use a ball bearing (BB) on your cutter. If you have a 1/2" shank Carbide cutter,
                plan on mounting a R 8 bearing on the shank above the flutes , or get a carbide router bit that has a BB at the tip.
                Now, get a wood router and use a rod or wire to cut a arc in a hardwood piece at 60 inches or whatever radius is needed to generate the desired arcs.
                Now fasten the wood pattern to the piece and let the BB follow the arc. If the BB is on the shank, then the pattern needs to be above the work piece .
                You may want to use aluminum instead of wood for the pattern as routers have no trouble with cutting that metal.
                Basically you will have a Tracer Mill operation
                Don't forget to add the difference in radius of the cutter and the BB to your calcs
                Rich

                added last sentence
                Last edited by Rich Carlstedt; 09-13-2020, 06:05 PM.
                Green Bay, WI

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                • #9
                  Use a spreadsheet to calculate coordinates along the tool path. You have to include tool diameter in the calcs. Dial in the coordinates then plunge the end mil. Rinse and repeat. The larger the endmill the lower the scallop height between cuts. Aster doing all that math and dialing in the cut locations (maybe at .050 spacing) you are going to wish you had it lasered or water jetted.

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                  • #10
                    X2 on the laser cut and just clean up the edges with a file. Unless you have a *really big* mill available and can swing a 31" radius from the cutter to the table. I know of one shop in my area that can do this on one of his lathes, he can swing parts up to 20 feet.

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                    • #11
                      Do you mean the radius faces are in the cross section like this?
                      You may only view thumbnails in this gallery. This gallery has 1 photos.
                      I just need one more tool,just one!

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                      • #12
                        Close Weird, but he said 1/2" thick material and 2 inches wide and 15" long
                        Rich
                        Green Bay, WI

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                        • #13
                          A decently rigid pivot 61-inches from the center of your roughed out blank
                          and a 20-foot cheater can give the term "manual feed" new meaning.
                          With a few folks with good machining instincts/experience and the finish
                          will be perfect.

                          note: the pivot is mounted on an extension on the table
                          so that you can fine tune position the pivot at different distances
                          from the cutter.
                          Last edited by Astronowanabe; 09-14-2020, 12:11 AM. Reason: can't spell, think slow
                          --
                          Tom C
                          ... nice weather eh?

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                          • #14
                            I would not even start to consider it from that description. An actual drawing with at least three views, actual TOLERANCES, and a definite alloy would be a requirement if done in my shop.

                            I don't have a DRO so I would probably do the calculated step thing. I would consider using a milling cutter (0.5 to 1 inch diameter) first for a rough cut and then a large diameter abrasive drum (5 to 10 inch diameter) for the final so that the hills and valley would be minimized.

                            It would not be cheap.



                            Originally posted by Dan_the_Chemist View Post
                            A small amateur observatory needs a SS part that is about 2" wide by 15" long and 1/2" thick, and needs to have a 60.00" concave radius milled on on side and a 62.00" convex radius milled on the other side (plus a few mounting holes).

                            Any ideas on how to do this without CNC?
                            Paul A.
                            SE Texas

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

                            Comment


                            • #15
                              Originally posted by wierdscience View Post
                              Do you mean the radius faces are in the cross section like this?

                              What you have labeled as 2.00 is 15.00 long, and what you have as 0.5 is 2.00 wide, and 0.5 thickness is in the axis away from you.

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