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Cutting circles

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  • #16
    Simplest cheapest circle cutting attachment for the torch is, electrical "bug nut" (splicing bolt) with nail brazed on head.

    Bug nut stradles torch tube and nail rides in center punch mark. Adjust radius by sliding bug nut on torch tube.

    Could also hose clamp, bent nail to torch tube but its not too solid.

    It helps to use some kind of turntable, so torch remains stationary, prevents fouling hoses.


    • #17
      Easiest way is to blank them out with a punch press. But if you don't happen to have at least a 125 ton punch press and the tooling, then you can trepan the circle easy enough on a lathe. The biggest mistake people make when trepanning is too fast of speeds. The plate must be held in the middle securely and plenty of coolant.
      I'd go into more detail but I can't give away our secrets.


      • #18
        I like water jet and laser cutting. Laser cutting does not warp the material at all (a good thing to remember). Water jet leaves a frosted surface on thick aluminum (the cuts) and slightly distorts the Aluminum from the pressures involved.

        Blanking on a punch press distorts the edge of the metal considerably.

        Cutting by torch or plasma can change the material properties in the heat affected zone.


        • #19
          Actually, the waterjet creates very little distortion, and even then only on thinner stock. Usually if I get a part "distorted" out of the waterjet, it's a factor of inherent stress in the rolled or extruded aluminum billet. I used to have a problem with the blanks cut from the ends of sheared barstock "cupping" a little, but the blanks from the center of the bar were dead flat.

          The 'jet actually applies very little force aginst the material- it's basically just a vehicle to drag the abrasive past the kerf.

          Laser cutting typically doesn't distort the thinner materials, as there's less loitering time. Cutting the thicker materials usually does induce some heat distortion, but usually a little less than a CNC plasma cutter.
          Doc's Machine. (Probably not what you expect.)


          • #20
            That does it! I'm off to purchase a 20,000 psi water pump and some cheap towels. I can probably EDM some tiny holes in my carbide boring bars to use as nozzles, hmm. Kidding aside, I've heard that water-jet cutting is noisier than stink, is that true? Is it practical for an HSM guy to build his own w-jet system?
            I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-


            • #21
              It's pretty noisy all right. Most cutting actually takes place under water- the cutting table (at least on the unit I'm familiar with) has a variable level tank. You set the parts up "dry", then flood it. That keeps the spraying and the noise down.

              And only 20K? I'm told this one starts at 50K psi, and if it drops down to less than 42K, they pull the pump down and rebuild it.

              If you can make a pump that can push water to 50,000 psi, and find Sapphire nozzles with an .015" orifice, the rest of it- the CNC 2D positioning, the cutting table, and the grit applicator- is relatively easy if you want to build one.
              Doc's Machine. (Probably not what you expect.)


              • #22
                How about using a Tesla pump to get the pressure for water jet cutting?
                A lot simpler than the hydraulic piston pumps.

                Someday when I have the time (never ) I have to try that.


                • #23
                  I wish Tesla and Einstein were both alive today, we could pose the pressure requirement to Tesla, then ask Einstein if theoretically, the water jet could exceed the speed of light. hmm. 50,000lbs pressure is a tad more than my best water pump can do.
                  I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-


                  • #24
                    I did some installation work for a guy who once ran a waterjet cutting firm. He mentioned to me that there were some pressure washer pumps on the market capable of 40KPSI that he thought would work great for water jet cutting.
                    They were a lot cheaper than the dedicated waterjet machines available then (8 years ago)
                    The machines he was using went up to 80 KPSI if I remember correctly. One of the big expenses was the grating that the workpieces laid on.
                    They got eaten up pretty quick.


                    • #25
                      I'm pretty sure that the first guy to ever build one of these didn't have a million dollars to spend. It really isn't fair of Thrud to suggest laser and water jet cutting without telling us how to build one in our HOME WORKSHOPS. I'm going to throw some numbers out and suggest a way to do it (just speculating.) Suppose you had an 8 ton double acting ram and the rest of the stuff to run it. If this modestly sized ram where used to drive a 1/2" rod in a long cylinder the pressure could reach 80,000 psi. Two rods could work alternately for a continuous output. I don't know if check balls work at those pressures without special provisions but the pressures are achievable. Making the orifice inexpensive and easily replacable could be a challenge. I shy away from sapphires. It would be cool if someone could design one for the home builder.


                      • #26
                        Pressure washer pumps at 80 kpsi. Sounds like a way to cut door and window openings through concrete. How would you clean siding with it? Scare the dirt off?
                        I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-


                        • #27

                          What you described is pretty much how waterjet pumps are built.


                          The pressure washers were run at 40 KPSI and with a fan spray nozzle.
                          It takes an amazing amount of pressure to remove some types of grime from New York's buildings.