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Hardened steel cutters

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  • Hardened steel cutters

    Greetings group. I'm new here, and far from an accomplished machinist. Just an old retired guy that likes to make things.

    I recently became fascinated with metal spinning and have learned to form a blank onto a mandrel with less than 30% failure rate, way down from the original 75-80%. So, now that I'm becoming so down right proficient I find I need a way to cut circles quickly and efficiently for use as spinning blanks.

    At one time a tool called a 'circle shear' was readily available from more than one mfr of spinning equipment, but these things are few and far between and when you do see one on eBay, they go for lots of money. There are also lots of designs, suggestions, plans and advice on making one around the web, many of which I've studied, thus I've come to the conclusion that since time is on my side, I can make one of these things. The rub is ....

    The cutters need to be fairly hard steel. High carbon steel would probably be OK for moderate use on non ferrous materials like light ga copper and softer alloys of aluminum, but eventually I'll probably decide to risk spinning some ferrous sheet metal as well. So I suspect the cutters need to be pretty hard.

    Picture a can opener on steroids is the best way to describe the cutter action on these things. I suspect a diameter or 1 - 1 1/2" with the outter perimeter turned to a slight slope on one or both(?) of the cutter wheels.

    It was suggested to me in another forum that dumpster diving in a junk store for an old hydraulic cylinder would yield a solid shaft of some pretty hard material. Annealed to workable hardness in my lathe for machining, then heat & quench to restore the hardness. I've also read about case hardening which I understand involves applying some sort of powder material to the heated material. And/or flame hardening with soot from my torch.

    Sorry for the lengthy post , - thanks for any advise and guidance
    Skagit Valley WA

  • #2
    I use bimetal circle cutters. They do a good job and provide good circles. If you have a small milling machine you can set them up and delete the centre drill bit and get a complete circle without a hole in the centre. Bimetal will work on all metals. But I dont know about spinning other than brass. You can get a range of sizes. The ones I have are made in USA.BLU-MOL bi metal hole saws.Made by Greenfield Industrial Saw blades. Evans,GA 30809.The box they came in had enough data for use on speed and feed.Like a 3and5/8th"hole saw in tool SS should spin at 45rpm. In Brass 120rpm. My biggest is 31/2"but the box suggests that they go up to 6"dia. Maybe I got that interpretation wrong. a phone call ought to sort it anyway.
    hope this is some help.


    • #3
      Hydraulic rod is 1045 steel. You may not need to anneal it unless you happen upon an induction hardened piece -- you'll know it if you do. It'll harden just fine.

      I don't think case hardening is the way to go for cutters. You'll need to stone them after heat treat and you may wear through the case while doing that or resharpening them.


      • #4
        <font face="Verdana, Arial" size="2">Originally posted by bobbybeef:
        I use bimetal circle cutters. </font>

        My circles need to be in excess of 10" for the spinning I'm doing. I wonder how safe (unsafe) a home made fly cutter would be for something like this?? The only way I've been getting 'circles' up to the present is to cut them out with snips, mount them on the lathe then spin a bit onto the mandrel then trim true. This works but is a lot slower and sloppier than it really has to be.

        Skagit Valley WA


        • #5
          <font face="Verdana, Arial" size="2">Originally posted by david_r:
          Hydraulic rod is 1045 steel....
          That, then, would be sufficiently hard for the type of cutting I'm anticipating? I don't know a great deal (obviously) about steel and its alloys.

          Skagit Valley WA


          • #6
            Could you make a set up to carry a tool bit or piece of High Speed Steel rod, w/ cutter ground on end?


            • #7
              I'm not sure a case hardened cutter is the way to go. It might be OK for wear but it of course will not support the same load without deformation and blunting of the cutting edge. I've never hear of case hardening cutters before.

              A piece of silver steel from your local metal supplier would probably be the best way to go. Most would class this as the "standard" method.



              • #8
                I have made sheet metal "blank" cutters by using a home made hole saw.I have done 11" blanks with this method.

                Using an aluminum or mild steel 1/2" thick base. Cutting a groove in the base that will hold bandsaw blade stock to the thickness or the blade and diameter of the blank you need.

                Drilling and tapping a series of perpendicular holes around the perimeter to hold the "blade" in the groove leaving it protrude to what ever I chose by cutting the depth of the slot to my preference.

                in this you may cut a number of "blank" sizes in the one disk as long as you can leave enough stock between sizes to drill and tap the holding screws in from the side.

                It is handy however; to have someone a band saw blade welder accessible for welding the blades in a circle.

                I hope perhaps this can help.

                If it's not broken, why do I keep trying to fix it....
                Member C.A.L.S. Balt'
                If it's not broken, why do I keep trying to fix it....


                • #9
                  I would second using what we in the US call drill rod. It is hardenable roundstock that is used to make drills & other tooling. It is readily available from most tool suppliers in a wide range of sizes.

                  The downside is it is usually only available in 36" lengths. But then you would have plenty to experiment with.
                  Jim H.


                  • #10
                    If I needed some perfect circles I'd use a flycutter in a drill press. I'd start with square sheet metal piece, clamp it in the corners and cut out the center using a flycutter mounted in the drill press. I'd have something like masonite or hardboard under so as not to damage the drill press table.

                    Don't think I'd want to make mass quantities this way but by facing the cutter right, you can cut 2 or 3 at a time

                    (most flycutters for drill presses let you remove the centering drill bit with an allen screw)

                    My way of doing it is only good for 6 inch or smaller but is infinitely adjustable. Norman Warfields idea should work pretty neat for much larger sizes.

                    [This message has been edited by Your Old Dog (edited 10-13-2005).]
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                    • #11
                      How about a cheapo 'hobby' bandsaw with centreless circle cutting jig. Just 2 thrust bearings, top and bottom with a disc of friction material on each and some sort of clamping arrangement. Highfield lever or eccentric is quick and easy. Set up the jig on a sliding table and cut any radius you want. I've done this with acrylic, ply, fibreglass PCB blanks etc.
                      Rgds, Lin


                      • #12
                        I recently cut some 3" circles on my 10 " lathe. I bolted a piece of wood to the backplate and screwed the sheetmetal blank to the wood. Adjusting the cross slide allows circles of up to say 9" to be cut from the blanks without a center hole. You do have to be careful when finishing the cut so the circle doesn't get away from you.


                        • #13
                          There was an adjustable hole cutter for sheet
                          metal ducts that used two pipe cutter type
                          wheels and a heavy backing disk. It needed
                          a center hole through the sheet metal for the
                          bolt that forced the cutters against the disk.
                          That would work if your sheet is thin enough
                          and you can stand the center hole in your blank. Charlie, also new here


                          • #14
                            The sheet metal trade uses various ways to cut a circle.
                            The lowest cost is a set of aviation snips.
                            One cuts curves easily to the left and the other cuts easily to the right. How you use them is to learn how to get the feel of the appropriate lean the operator applies to the tool. You layout your circle and snip around.

                            There are "power snips" for a couple hundred dollars that have short strokes and nibble/ shear their way around.

                            Already described is the through hole type, rolling wheel, circle "cutter"

                            Using a deep throat "clamp" rig the rolling wheel can work without the center hole.
                            There are sheet metal folks that manufacture that rig to make "drum heads" from sheet stock there are "jaws" that cut and "jaws" that form.

                            If you enjoy rigging stuff you can get some structural channel and some plate, and then make up a parallel rail frame with a plate on the base pair and a bushing between and on the end of the arm pair to accept your rolling wheel Parting arm.
                            The back end of the "clamp/arm" rig needs to be stout. Possibly doubling the height of your channel and/or putting cap plates between the channels.

                            A drill press will make a light duty rig similar to what is suggested above. I say light duty because the usual DP column will deflect too far and too easily with the loads involved.

                            Pipe and tubing cutter wheels are available from almost any industrial supply outfit.

                            HTH Ag

                            [This message has been edited by agrip (edited 10-13-2005).]

                            [This message has been edited by agrip (edited 10-13-2005).]


                            • #15
                              1045 will harden to about 50 or so RC. Say as hard as the blade on a good knife. I think that would be hard enough to do what you need. They aren't going to be as good as tool steel but the price is right.

                              If you just wanted some blades, you might try calling harbor freight and seeing if they stock the blades for this.
                              If they have them in stock, they'll be inexpensive and fast. If they have to come from China, who knows how long that would take. I don't know if they'd be suitable for your application but thought I would throw it out there.