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Clean easy way to cut an 11" dia circle in sheet of 0.025" steel?

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  • Clean easy way to cut an 11" dia circle in sheet of 0.025" steel?

    I can think of lots of slow labor intensive ways to do this, like using my air nibbler and then a die grinder with a large diameter stone, or making a tram with a cutter on the end and draw it around and around till I'm through. Any good ideas?

    FWIW, this is but step one in another stupid idea to get somewhere. I want to make a very shallow bowl of 1/16" thermoplastic 11" dia with a radius of 70". This round cut in steel is to make a frame for the vacuuformer plate to see if I could control the droop from heat well enough to get close to my 7/32" target.
    Location: Jersey City NJ USA

  • #2
    Jig saw, trepanning tool, rotary table, mount on lathe faceplate
    Last edited by buffdan; 05-20-2021, 11:48 PM.

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    • #3
      piece of string and a razor knife. String is your radius, nail it in the center and keep pulling the knife around... it'll break clean after several passes around.
      25 miles north of Buffalo NY, USA

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      • #4
        Originally posted by nickel-city-fab View Post
        piece of string and a razor knife. String is your radius, nail it in the center and keep pulling the knife around... it'll break clean after several passes around.
        Variation on the tram I mentioned. buffdan can't mount a 12"x 18" sheet on a 10" lathe nor on a table of a Jet 16. Jigsaw no better than my nibbler.
        Location: Jersey City NJ USA

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        • #5
          Rough it with tin snips.
          put a nail through the center and nail it to a piece of plywood or what ever and then mount the wood to a disk or belt sander table and grind/sand the OD to size.

          Rich
          Green Bay, WI

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          • #6
            Originally posted by gellfex View Post

            Variation on the tram I mentioned. buffdan can't mount a 12"x 18" sheet on a 10" lathe nor on a table of a Jet 16. Jigsaw no better than my nibbler.
            I know try it anyways -- your options are kinda limited. I do know a razor knife with several passes makes a nice clean cut, not all jagged. I've seen how dome heads are formed for pressure vessels -- ran such a machine once -- and believe it or not, it's the same principle.
            25 miles north of Buffalo NY, USA

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            • #7
              Originally posted by nickel-city-fab View Post
              piece of string and a razor knife. String is your radius, nail it in the center and keep pulling the knife around... it'll break clean after several passes around.
              I was going to say something more rigid than string, like a strip of wood make like a trammell to hold the Exacto knife perfectly rigid and pin stick in the center of the circle. Just keep spinning until you scored through enough to just break it. I do this with aluminum all the time.



              JL......

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              • #8
                Are you looking for the round, or a round hole in a flat plate?
                I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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                • #9
                  Originally posted by Rich Carlstedt View Post
                  Rough it with tin snips.
                  put a nail through the center and nail it to a piece of plywood or what ever and then mount the wood to a disk or belt sander table and grind/sand the OD to size.

                  Rich
                  That would be my approach more or less. I'd cut slightly oversize with snips then set up couple of discs of plywood. One in my lathe chuck and one as a presser disc. Then pressure clamp the disc of metal between the two discs using pressure from the tail stock using a live center to push the "free" disc against the metal and the plywood disc held in the chuck. Turn the edge to size and yer done.

                  Not my idea. Just an adaptation to suit your sizes of the pressure chucking video from Joe Pie.
                  Chilliwack BC, Canada

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                  • #10
                    Originally posted by JoeLee View Post
                    I was going to say something more rigid than string, like a strip of wood make like a trammell to hold the Exacto knife perfectly rigid and pin stick in the center of the circle. Just keep spinning until you scored through enough to just break it. I do this with aluminum all the time.



                    JL......
                    Again variation on what I said "making a tram with a cutter on the end and draw it around and around till I'm through".

                    For those confused, I need the hole not the disc.
                    Location: Jersey City NJ USA

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                    • #11
                      For those confused, I need the hole not the disc.
                      Sorry, that wasn't obvious.

                      How big does the sheet surround need to be? Can you hold it in your mill or could it be a moderate width donut in the lathe?
                      Chilliwack BC, Canada

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                      • #12
                        Sandwich it between two sheets of 3/4" plywood. Use a bunch of wood screws from the bottom and near the cut line but inside of it. Add at least four more at the corners if you can have them far enough from the area you need. You can use them to fasten the whole thing to the top of a wood bench or a pair of saw horses.

                        Then drill a 1/4" pilot hole in the top sheet of plywood and down into the steel. Use a wood router on a circle cutting arm guided by that 1/4" hole. Use a carbide bit to cut through the top plywood and steel and down a small amount into the bottom plywood. Disassemble the sandwich and you should be done.
                        Paul A.
                        SE Texas

                        And if you look REAL close at an analog signal,
                        You will find that it has discrete steps.

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                        • #13
                          Centerpunch lightly and draw your circle. Take over to shear. Make cuts all around close to the outside of your line but not touching it. Now go over to the belt grinder. Make sure you can see your circle well. Sand to the circle. It will only take a few minutes.

                          Or beg borrow or steal a Pexto circle shear.

                          metalmagpie

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                          • #14
                            not sure how any of this is easier/faster than a jig saw and file. If you don't have access to a laser/water jet/plasma or don't to send it out you use what you have...but those three are the quick and efficient ways to make holes in sheet

                            Centerpunch lightly and draw your circle. Take over to shear.
                            Would have been clearer if he asked how to make hole instead of circle, but that's what he wants - a hole, not a disk
                            in Toronto Ontario - where are you?

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                            • #15
                              Aviation snips. There will be some distortion. Cut most of it out first leaving 1/8 inch for a trim cut will work best. Straighten with hammer and clean up with a file.

                              I would use my plasma cutter and a template but assuming you don't have one or you wouldn't be asking the question.

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