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Cylinder square now with more lathe

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  • #46
    Originally posted by J Tiers View Post

    It is REALLY hard to lap by hand movements and not put in a "rocking point" like that, especially with a part that is fairly tall and thin. It just "wants to" tip as you work.

    If you could set up to lap via a disc or diamond plate on the lathe, then you could set up a v-block or similar arrangement that would hold the pin steady. That way, if you had an error, it would be consistent, and you should be able to correct it in a consistent, controlled manner by shimming etc.

    Johansen lapped the first gauge blocks on a converted sewing machine that drove a disc. It should work for you also.
    Well, that was a bust. But thanks for the ideas! Maybe I can crazy-glue my v-blocks on top of the cross slide and hold the part in with finger pressure. Will have to get some sort of "chuck-able" abrasive, or make something up... Welcome to the world of having limitations.
    Last edited by nickel-city-fab; 02-29-2020, 08:08 PM.

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    • #47
      Instead of the tape try metal shims super glued to to the low spots. The tape will squish where the shims will not.
      At the end of the project, there is a profound difference between spare parts and extra parts.

      Location: SF East Bay.

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      • #48
        Originally posted by danlb View Post
        Instead of the tape try metal shims super glued to to the low spots. The tape will squish where the shims will not.
        Now that you mention it, I wonder if tinfoil would work. Problem I ran into before was that the tape simply made a perfect "gasket" and peeled away on the hone. Right now I'm trying a setup on the mini-lathe, but I'm not expecting much. Using superglue.

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        • #49
          All that did was screw it up even worse, dammit! Try again... maybe Start over with the honing plates by hand... OUT by 20 thou on one side now. Folks, you can NOT put thin in the lathe without tailstock support. Which is right in the way of what I need to work on. Don't bother trying to chuck a part that is as big as the machine itself.
          Last edited by nickel-city-fab; 02-29-2020, 10:08 PM.

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          • #50
            Hrmmm... seems the only way to make it happen in the lathe is, to remove the chuck (piece of garbage anyhow) and superglue the piece onto the spindle face. Then clamp a small stone into the tool post and feed it in very slowly, low RPM.

            The limiting factor is the fact that the piece takes up the entire practical envelope of the machine, and definitely needs support at the far end... right where I'm working. superglue and extreme care might work in a pinch though.

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            • #51
              Nah, scratch that. I no longer have the "roof peak" geometry, but I do have a consistent 15 thou lean on positions 3 and 4... maybe this time I'll get it. The diamond stones are saving my butt here.

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              • #52
                OK, I've managed to get it back to 0,0 on positions 1 and 3. But this time I don't have the funky geometry. Will deal with positions 2,4 tomorrow. They have a difference of around .002.

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                • #53
                  I have one of the little 7 X 12 lathes at home like yours, and ended up changing the original 80 mm chucks, which were not great for a 100mm four jaw and a better 80mm three jaw. They are both SANOU, not the best, but noticeably better than the originals. Having workshop facilities at the museum made it easy for me to modify the 100mm to fit directly on the spindle. It is worth googling "mini lathes" for lots of ways of improving these machines.
                  I looked around at home and found a cheap copy of the DMT diamond laps with a much coarser 150 grit. I will stick it on another parting blade and get the end square in a fraction of the time. Then I will resort to the fine DMT to get a superior finish. The witness marks are all at the periphery which is exactly where it will be most stable.
                  The pin is in a 6" lightweight four jaw chuck with a considerable unsupported length, which would not face off at the end without support. I could use the fixed steady with the roller bearing tips, but prefer the gentle lapping method. The forces are minimal with the flexibly mounted lap. Before I resume the lapping on Wednesday, I will check the runout of the pin in the chuck.

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                  • #54
                    Originally posted by old mart View Post
                    I have one of the little 7 X 12 lathes at home like yours, and ended up changing the original 80 mm chucks, which were not great for a 100mm four jaw and a better 80mm three jaw. They are both SANOU, not the best, but noticeably better than the originals. Having workshop facilities at the museum made it easy for me to modify the 100mm to fit directly on the spindle. It is worth googling "mini lathes" for lots of ways of improving these machines.
                    I looked around at home and found a cheap copy of the DMT diamond laps with a much coarser 150 grit. I will stick it on another parting blade and get the end square in a fraction of the time. Then I will resort to the fine DMT to get a superior finish. The witness marks are all at the periphery which is exactly where it will be most stable.
                    The pin is in a 6" lightweight four jaw chuck with a considerable unsupported length, which would not face off at the end without support. I could use the fixed steady with the roller bearing tips, but prefer the gentle lapping method. The forces are minimal with the flexibly mounted lap. Before I resume the lapping on Wednesday, I will check the runout of the pin in the chuck.
                    Your plan should work well, I would think. In my lapping, I find that flooding the stone with oil helps a lot -- I'm using a cheap diamond lap which would clog up. The unsuported length can be a pain, I found that I had to use an improvised "center" when turning my relief on the bottom, as well as using fresh carbide and a very slow speed. I would *love* to get a 100mm 4-jaw, and I have been planning to do so for a year now. Little Machine Shop has everything for my lathe.

                    In my case, I finally got it "square" to less than a tenth last night at 2 AM. I'll post another thread about that.

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                    • #55
                      I would highly recommend getting a 100mm four jaw for your lathe. It would be big enough to hold one of those pins at one end to lap the end. Getting the whole length of the pin running parallel to the axis of the spindle is a slow process. You get the end next to the chuck running to 0.001" or less without tightening the jaws too much, and then check the outer end. Gentle taps with a nylon hammer will slowly get the end better, and then back to the jaw end for fine fettling. This process is repeated until the pin is as parallel as you can get it. I was content with 0.0001" tir at either end, that was more than good enough for anything we will ever need at the museum.

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                      • #56
                        Originally posted by old mart View Post
                        I would highly recommend getting a 100mm four jaw for your lathe. It would be big enough to hold one of those pins at one end to lap the end. Getting the whole length of the pin running parallel to the axis of the spindle is a slow process. You get the end next to the chuck running to 0.001" or less without tightening the jaws too much, and then check the outer end. Gentle taps with a nylon hammer will slowly get the end better, and then back to the jaw end for fine fettling. This process is repeated until the pin is as parallel as you can get it. I was content with 0.0001" tir at either end, that was more than good enough for anything we will ever need at the museum.
                        Very much like what I was doing, only I had the 3-jaw gripping on the ID. I used a lump of lead to gently knock it in true less than .001. Then using the diamond laps laying flat on a board and just pushing it by hand bearing down on the high side.

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                        • #57
                          The runout doesn't matter, as long as it is the same at both ends at the same time. A runout of 0.005" at the jaws would be ok as long as the high spot of 0.005" was in exactly the same position at the other end. Of course, keeping the rpm of the spindle low would be important with the eccentric running.

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