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Free turning a half ellipse in the lathe

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  • Free turning a half ellipse in the lathe

    Hi Everyone,

    This may be old news to people but it is new to me.

    I just posted a video on YouTube showing a method I stumbled across to shape a form I am making for metal spinning a clock pendulum bob.

    Basically I am using a metal lathe as a wood lathe to shape a complex curve and was surprised to find it easy and simple to do. I was also pleasantly surprised to find the finish was great.

    This saved hours of blending with a file.
    Best wishes to ya’ll.



    "To invent you need a good imagination and a pile of junk" - Thomas Edison

    "I've always wanted to get a job as a procrastinator but I keep putting off going out to find one so I guess I'll never realize my life's dream. Frustrating!" - Me

    Location: Bustling N.E. Arizona

  • #2
    Very cool stuff Jim! Let me be the 1st *NOT* to scold you for wearing gloves. We big boys do what we think is right and take full responsibility for doing what makes good sense to us. Oh, & make sure to post a video of the spinning. That really interests me.

    "Accuracy is the sum total of your compensating mistakes."

    "The thing I hate about an argument is that it always interrupts a discussion." G. K. Chesterton


    • #3
      Just like turning on a wood lathe. If it were me I would make an extension for the end of the tool holder so I would have a little more leverage against it, or I would mount a piece of flat bar over the top of it with just enough clearance to slide the tool holder around, that would take a lot of load off the hands. Holding a short tool holder like that is risky business............. also ............lose the gloves !!!!!!!!! nothing like wearing something that can get snagged.



      • #4
        Nice finish!

        Along with the others and no gloves. As well as extending the tool so your fingers aren't right in the mix. If the tool did grab and pull in you don't want your fingers to be right there first thing to get pulled in.


        • #5
          Was the cutting edge exactly on the center line? looked to be above the CL to me, but it wasn't clear.
          Lynn (Huntsville, AL)


          • #6
            I'm curious what meterial is being cut/shaped in the video? Is that stainless?


            • #7
              Nice technique for producing an approximation of an ellipse. I have always said that the skill and precision is in the fingers, not the machine.

              Nix on the gloves. And nix on putting your fingers, glove or no glove, right at that junction of spinning metal and the fixed plate with a gap just small/big enough to pinch some skin in there. Sorry, but I am not going to hold back on that. Perhaps he needs some heat in his shop.
              Paul A.
              SE Texas

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


              • #8
                I agree that the gloves are a liability and could be pinched between the spinning part and the tool rest, but otherwise this is an interesting technique that I have not tried. It might be possible to add a "bridge" on the right side of the tool rest to secure the far end of the cutting tool and still allow it to be positioned by hand, and perhaps make a grip for the tool to keep fingers away from the pinch point. Also, perhaps you could glue the template (just half of it, actually) to the tool rest so that you could see how close you are while machining the surface. It would probably work best if the template were made of thin, slick material like polyethylene or Teflon. Thanks for the video - it "turned" out pretty good!
                Paul , P S Technology, Inc. and MrTibbs
                USA Maryland 21030


                • #9
                  yeah, the gloves creeped me out...but fun to see the free hand approach. Like using a giant watchmakers lathe
                  in Toronto Ontario - where are you?


                  • #10
                    Hey Jim, yer gloves don't bother me! Looks like a good way to keep those hot chips off your fingers. With a tight gap like that I don't think heavy leather gloves are much of a risk. Sometimes people get all caught up in general rules without evaluating specific circumstances. Like the ones who shout about NEVER EVER!!! using compressed air around their machines. Hell yeah, I use air all the time but I'm careful where and how much. Same with gloves.
                    Last edited by chipmaker4130; 12-05-2015, 08:33 PM.
                    Southwest Utah


                    • #11
                      Aforementioned criticisms appreciated so not repeated, the method obviously works, I think could be improved a little, another bar above the tool say 1/2 X 1/2" square, as long as the tooling plate is wide, a couple of spacers, tool thickness plus a very small clearance to allow the cutting tool free movement transversely but to prevent it being picked up if it dug, my fear is that if it dug it would raise off the support plate and trap.
                      Also a longer extension on the tool to get away from poking squishy sausages near a fixed plate and a spinning thing, having fingernails ripped out is best saved for when your hiding information from super villains.
                      It works but try to marginalise the risks.
                      I'm not going to tell you not to wear gloves but as an experiment, take one off an present it to the gap between the spinny thing and the hard fixed thing, it's really impressive!


                      • #12
                        I think it would be difficult for thick leather gloves to be pulled into the gap, but it might be instructive to try it as you suggest. Much depends on the coefficient of friction of the glove and the spinning surface, and I think it would take a good bit of pressure to make it "stick". The leather is probably too thick to fit in the gap, especially when squeezed into a double layer. The main concern with gloves and loose clothing around a lathe, I think, is for something to snag on a sharp edge of a chuck jaw, which would then pull the item along with its wearer, under the chuck and into the pinch point with the ways. At that point it resembles a meat grinder.
                        Paul , P S Technology, Inc. and MrTibbs
                        USA Maryland 21030


                        • #13
                          A wood lathe uses hand held tools with long handles on them for a good reason. So, if one wants to do free hand machining of metal (and keep one's fingers), just make some free hand machining tools and and a tool brace like this for the compound...

                          Last edited by Mike Burdick; 12-06-2015, 01:08 AM.


                          • #14
                            Or just call it a graver and use it like it's been done since the mid 1700's


                            • #15
                              Originally posted by Mike Burdick View Post
                              A wood lathe uses hand held tools with long handles on them for a good reason. So, if one wants to do free hand machining of metal (and keep one's fingers), just make some free hand machining tools and and a tool brace like this for the compound...

                              Well done, that's exactly what I was trying to describe in my own rambling way, good catch