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Top Dead Center of a Sphere(?)

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  • Top Dead Center of a Sphere(?)

    I was cutting a LED light bulb the other day. Cutting the bottom off was a piece of cake. I placed a piece of sandpaper on a granite countertop to make it nice and flat. I ended up drawing a couple of concentric rings on the top to try and find TDC, then used a hole saw by hand slowing turning it until I bored the top. Everything seemed to work out nicely. I was wondering if there's another way of finding TDC without a lathe or mill?
    Attached Files

  • #2
    Dead center is a function property of an eccentric linkage.
    What are you asking?

    -D
    DZER

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    • #3
      Put a light smear of hi spot on a height gauge scriber and touch off on it. Alternatively you can blue/sharpie up the sphere and rub off the top with the height gauge.

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      • #4
        Hum, how to find the top of the sphere without machining equipment.

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        • #5
          Originally posted by Dan Dubeau View Post
          Put a light smear of hi spot on a height gauge scriber and touch off on it. Alternatively you can blue/sharpie up the sphere and rub off the top with the height gauge.
          Thanks Dan. All of my machining equipment is in storage. I just moved to another state. I like the concept which you mentioned. I'll just have to modify another way of accomplishing that which I have a good idea brewing right now.

          Sweet
          Last edited by Smokedaddy; 01-18-2022, 10:17 PM.

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          • #6
            A level.

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            • #7
              Originally posted by Bob Engelhardt View Post
              A level.
              I like that. Nice and simple, and should get you close enough.

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              • #8
                Originally posted by Dan Dubeau View Post
                Put a light smear of hi spot on a height gauge scriber and touch off on it. Alternatively you can blue/sharpie up the sphere and rub off the top with the height gauge.
                I'll just use my scope to mark the TDC after placing the cut bulb on the stage. Great idea, thanks again.

                Problem solved, two heads are better than one in this case.

                -JW:
                Attached Files

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                • #9
                  My first thought at seeing the partial globe on the viewing stage was "why is he using a microscope to find TDC? But to my credit that thought only lasted about 0.2 of a second when the "light dawned"....

                  What a tricky trick to make a nice diffuser! ! You one smart cookie!

                  Your trick for making the ring around the top is also your method for easily finding the top center. You just needed a taller block. Or with too tall of a block just hang the pen down and pass the globe under it while slowly lowering the pen until you get a few short touch marks on the top. It would have been close enough for government work.
                  Last edited by BCRider; 01-18-2022, 11:32 PM.
                  Chilliwack BC, Canada

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                  • #10
                    Do the same as in your first photo, but add a Vee block to act as a bearing for the sphere to rotate in.
                    I just need one more tool,just one!

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                    • #11
                      Lay a 6" scale on top, when level mark at 3" that's center.
                      John b. SW Chicago burbs.

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                      • #12
                        Set a tube, centre the tube, drop ball in tube, ball at TDC
                        mark

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                        • #13
                          For the intended purpose, a sheet of Rosco or Lee diffusion gel would have worked without going through all the bulb BS?
                          https://us.rosco.com/en/diffusion-ma...o-applications

                          Tracing paper or even TP works as a
                          diffusion material for lighting.
                          Last edited by reggie_obe; 01-19-2022, 11:31 AM.

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                          • #14
                            Is that a Pioneer RT-909 I spy in the background ?

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                            • #15
                              Still can't figure out what is dead about the center.
                              I bet no one else has either.
                              I was thinking just grind a flat on the globe by
                              holding it against the belt sander. It seems by
                              how you are using it, micron precision is not needed.

                              -D
                              DZER

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