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I made a Repeat O Meter

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  • I made a Repeat O Meter

    Well, after thinking about making it from Aluminum I dug around and found some steel that wasn't doing anything. It didn't run fast enough and so I grabbed it.

    I'm going to discuss some of my design decisions and share a few observations. However, just as I sat down to type up my notes SHMBO stuck her head into my sanctum sanctorum and announced that she didn't feel like cooking and that we are going out to eat.

    So, I'll do all of that after I come back. Here are two pictures to whet your interest. What amazes me... I left it out of the dry cabinet overnight and it shows traces of light rusting. AIIIIEEEEEE... And I know the finish isn't the best. I figured I was only going to use this a very few times, so I didn't bother with the 200, 500, 2000 sandpaper stuff. It's milling machine finish.





  • #2
    Beautiful job! What are you going to use it for?

    Comment


    • #3
      Did you make the handles?

      (My primary interest is more woodworking than metal work.)

      Comment


      • #4
        Nice job. The finish does not matter except on the bottoms of the feet so don't apologize for that.

        And, what did you finally decide to do for the feet? Photo please.
        Paul A.

        Make it fit.
        You can't win and there is a penalty for trying!

        Comment


        • #5
          Originally posted by Paul Alciatore View Post
          Nice job. The finish does not matter except on the bottoms of the feet so don't apologize for that.

          And, what did you finally decide to do for the feet? Photo please.
          And,what did use for the flexure?

          Comment


          • #6
            Originally posted by 6270 Productions View Post
            Did you make the handles?

            (My primary interest is more woodworking than metal work.)
            Yes. I started in woodworking, and used to demonstrate old fashioned woodworking at a living history center. I've spent hours and hours on a spring pole lathe so my Jet wood lathe is a real luxury.

            I have a lot of odd cutoffs of oak and maple that I got from the dumpster of a furniture making factory. So, it's easy to make wooden handles for things.

            Comment


            • #7
              Originally posted by Tungsten dipper View Post
              Beautiful job! What are you going to use it for?
              I got a 36 by 48 granite surface plate for nearly free (less than $100). After I built the stand and got it into place I began to ask the question "Just how good is this thing?". It had been certified as an A grade plate in 2014, but that was 5 years ago. Somebody could have used it to lap things with diamond powder since then. So, I made a repeat o meter. I'll show more details later, but right now let me just say that the plate is really good, except the last few inches of two opposite corners.

              Comment


              • #8
                That's a work of art. Is there a way to calibrate that? Do you need a certain size one for large surface plates?

                JL....

                Comment


                • #9
                  Originally posted by Stu View Post
                  And,what did use for the flexure?
                  I went with a flexible strip milled out of the bar.



                  Top Lipton had tried an inset piece of flexible bronze spring stock, but he had to drill and tap 14 holes in the steel and the bronze spring stock. That seemed like a lot of bother... It's interesting to note that while he proposed it in an early video and showed it being built, he never mentioned it again in later videos in collaboration with John Saunders. They noted the problems of having a stress riser at the base of a long cut, so they devised a method based on a drilled hole and a saw cut.



                  I liked this, but I was a little afraid of trying to predict the necessary thickness of the web that formed the flexure. After all, it was a piece of "gawds only knows what" steel. It could be cold rolled or 4140 or who knows.. So I did some modeling with Fusion 360. My goal was to figure out a flexure that could be thinned to make it more flexible without making it susceptable to easy failure due to stress concentrations.

                  I modeled it using various types of steel and chose a value that would give 0.020 flexure under the weight of gravity without coming close to the elastic limits. First thing I noticed was that wider cuts gave greater safety margains... a narrow cut quickly exceeded the safety limits and could lead to failure, but a wide cut spread the stress out over a larger area and it worked better. So I decided on a 0.550 inch wide cut to leave a 0.060 web. This would probably be too stiff, but if I had a good jig set up I could remount it in the mill and thin it.

                  In practice 0.060 was too thick. I ended up thinning it to 0.035 to get the desired degree of flex.

                  The next thing is the location of the web. All examples I've seen have the flexure on the bottom. I thought about that, but it made the milling more difficult. I would have to hold it so that I could come within 0.060 of the bottom. If I left the web in the middle of the piece (as shown) it would be much easier to hold while using the mill.

                  However, there is a question that arises from having the flexure in the middle rather than the bottom. That is the effect of geometry - it's not on line with the feet. Well, neither is the one on the bottom, but a quick geometrical calculation showed that the parallax effect would introduce an absolute reporting error of about 0.000008 inches... Yes, that's a lot of zeros. I.e., if the meter said the probe-foot had risen 0.0001 inches it would be off by up to 0.000008 inches ... 8%. However, it's a consistant systematic error. I could live with that.

                  More details to come...

                  Comment


                  • #10
                    Originally posted by Paul Alciatore View Post
                    Nice job. The finish does not matter except on the bottoms of the feet so don't apologize for that.

                    And, what did you finally decide to do for the feet? Photo please.
                    Ah, the feet. Well, I went with 0.500 ball bearings pressed into holes that had been reamed with a 0.498 reamer I got off of eBay. I pressed them in after I cut the top channel for the flexure, but before I cut bottom channel for the flexure, and then used wet and dry paper to sand flats on the feet. Started with 200, then 500, and then some 2000.

                    The reason I did it in that order was to give myself a totally flat bottom when cutting the channel for the flexure from the top. Then, I didn't want to worry about having a floppy piece of metal while doing the pressing, drilling, tapping, etc., so I finished all the other steps before cutting the bottom channel.

                    I surprised and very unhappy at how much light rusting happened in just a few days. I left it out of the dry cabinet for just a few days. It's not even humid, and it's not going through that cold nights/hot humid morning cycle that leaves everything swimming in dew... It's sort of interesting that you can see the ghost of a note I made on the metal near the bottom foot. I had written the measured depth of each hole with Sharpie, but then I removed it with acetone before pressing in the feet. You can clearly see that the rust didn't affect that area. Odd.

                    Comment


                    • #11
                      Originally posted by Dan_the_Chemist View Post
                      It's sort of interesting that you can see the ghost of a note I made on the metal near the bottom foot. I had written the measured depth of each hole with Sharpie, but then I removed it with acetone before pressing in the feet. You can clearly see that the rust didn't affect that area. Odd.
                      Hmmm, you might have discovered something... Rust prevention by Sharpie. There are a couple more of those areas visible on your bottom, too. It's possible that the moisture came from your hands.

                      Comment


                      • #12
                        Originally posted by Dan_the_Chemist View Post
                        I went with a flexible strip milled out of the bar.



                        Top Lipton had tried an inset piece of flexible bronze spring stock, but he had to drill and tap 14 holes in the steel and the bronze spring stock. That seemed like a lot of bother... It's interesting to note that while he proposed it in an early video and showed it being built, he never mentioned it again in later videos in collaboration with John Saunders. They noted the problems of having a stress riser at the base of a long cut, so they devised a method based on a drilled hole and a saw cut.



                        I liked this, but I was a little afraid of trying to predict the necessary thickness of the web that formed the flexure. After all, it was a piece of "gawds only knows what" steel. It could be cold rolled or 4140 or who knows.. So I did some modeling with Fusion 360. My goal was to figure out a flexure that could be thinned to make it more flexible without making it susceptable to easy failure due to stress concentrations.

                        I modeled it using various types of steel and chose a value that would give 0.020 flexure under the weight of gravity without coming close to the elastic limits. First thing I noticed was that wider cuts gave greater safety margains... a narrow cut quickly exceeded the safety limits and could lead to failure, but a wide cut spread the stress out over a larger area and it worked better. So I decided on a 0.550 inch wide cut to leave a 0.060 web. This would probably be too stiff, but if I had a good jig set up I could remount it in the mill and thin it.

                        In practice 0.060 was too thick. I ended up thinning it to 0.035 to get the desired degree of flex.

                        The next thing is the location of the web. All examples I've seen have the flexure on the bottom. I thought about that, but it made the milling more difficult. I would have to hold it so that I could come within 0.060 of the bottom. If I left the web in the middle of the piece (as shown) it would be much easier to hold while using the mill.

                        However, there is a question that arises from having the flexure in the middle rather than the bottom. That is the effect of geometry - it's not on line with the feet. Well, neither is the one on the bottom, but a quick geometrical calculation showed that the parallax effect would introduce an absolute reporting error of about 0.000008 inches... Yes, that's a lot of zeros. I.e., if the meter said the probe-foot had risen 0.0001 inches it would be off by up to 0.000008 inches ... 8%. However, it's a consistant systematic error. I could live with that.

                        More details to come...
                        I always thought that the front piece was independent of the rear. I had no idea that the base was a continuous piece. These are used to measure surface discrepancies in the millionths in some instances and I would think any connection between the two base pieces would hinder it's accuracy by stiffness alone regardless of how thin the connecting section is. It's like a living hinge ! Why doesn't it free float??

                        Other thought ..... your not sure what the material is that you used, if it's not stable and decides to move over time won't that lead to inaccuracy??

                        JL.............

                        Comment


                        • #13
                          Originally posted by JoeLee View Post
                          I always thought that the front piece was independent of the rear. I had no idea that the base was a continuous piece. These are used to measure surface discrepancies in the millionths in some instances and I would think any connection between the two base pieces would hinder it's accuracy by stiffness alone regardless of how thin the connecting section is. It's like a living hinge ! Why doesn't it free float??

                          Other thought ..... your not sure what the material is that you used, if it's not stable and decides to move over time won't that lead to inaccuracy??

                          JL.............
                          The front piece needs to be able to move up and down at the end where the indicator is. That is, it's essentially tracking just the one foot at the front. Conceptually you could have just had an indicator out front riding on the surface plate itself but the surface texture would make it impossible to read. The front section just damps out all the tiny local variations.

                          I wouldn't expect material changes to affect it. The main body rides on a three point base so it's always stable. Even if you imagine a twist at the flexure, the front pad should still be able to map the broad hills or depressions of the surface plate. The only thing the repeat-o-meter couldn't ferret out would be a plate that has a slight, perfectly uniform concave or convex shape. Unless you can set the indicator on a verified flat surface, then move to the plate you're checking and find a uniform indicator change all over. Then verify that when you go back to your flat plate you once again have a zero indicator.
                          .
                          "People will occasionally stumble over the truth, but most of the time they will pick themselves up and carry on" : Winston Churchill

                          Comment


                          • #14
                            Originally posted by Dan_the_Chemist View Post
                            Yes. I started in woodworking, and used to demonstrate old fashioned woodworking at a living history center. I've spent hours and hours on a spring pole lathe so my Jet wood lathe is a real luxury.

                            I have a lot of odd cutoffs of oak and maple that I got from the dumpster of a furniture making factory. So, it's easy to make wooden handles for things.

                            You know how sometimes you think (imagine?) faster than you are reading?

                            I was just finishing the "spent hours and hours on a spring pole lathe" part of your sentence - - - and thought - - - He did those on a spring pole lathe???!!!

                            Then I finished the "my Jet wood lathe is a real luxury" part.

                            I love working on my lathe and - as I am sure you have discovered - making "only one" pieces are much easier than making "another one to match".

                            Nice job on your tool - although being a woodworker - I have no idea what you are supposed to do with the darn thing!


                            I know metal work is supposed to be expensive, but let me just say this. I have more invested in my routers and related bits than I do in my LeBlond lathe and related tooling.

                            Comment


                            • #15
                              Originally posted by 6270 Productions View Post
                              I was just finishing the "spent hours and hours on a spring pole lathe" part of your sentence - - - and thought - - - He did those on a spring pole lathe???!!!
                              I think the spring pole lathe is underrated. When I was doing it 8 weekends a year for years on end I could turn one piece wooden baby rattles of the style shown (the picture is a multi part... I did it from one solid chunk of maple). It's not that I'm a particularly gifted turner... it's just by the time you've done a few dozen it gets easy.

                              I have made table legs, stools, spinning wheel parts, etc., all on the spring pole lathe. It's really not that bad.

                              And it really builds up the leg muscles. I was young, single, and dating for much of that time. Being in good shape was a real benefit.


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