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Help! indicator driving me crazy.

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  • Help! indicator driving me crazy.

    Sometimes I just have to ask for help. I'm trying to re-align my lathe but the indicator won't play nice. To say that the indicator won't repeat would be an understatement. I'm not new to indicators or setups but this problem is driving me crazy. The indicator is a Mitotoyo and has a flat tip, the rod is 1" drill rod cleaned up with emery cloth, the mag base is strong and solidly mounted, the flex arms lock up real nice. the 1" rod is tight in the new Bison chuck. The indicator will not repeat. By that I mean it can swing from 0.025" to 0.055" one time then 0.035" to 0.067" then 0.032" to 0.050". If I set the indicator on 0.050" and mark the bar for reference the next time I rotate to the mark the indicator will not read 0.050". It might read 0.042" or 0.056". I've had similar problems but always found something wrong with my setup or something loose. I can't find anything wrong here.

    Can anyone see a problem with my setup or have a suggestion to solve my problem. Thanks in advance.

    Ron








  • #2
    I've never seen a flat tip used. Mine all came with a hardened steel ball tip. Can you put a ball tip on it?

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    • #3
      Can you grab the bar, shake it in different planes and make the indicator deflect significantly?

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      • #4
        If that three jaw is bell-mouthed to even a small extent it will cause exactly what you are seeing. Try what Pherdie suggests, the bar will have some flex but should return to its original place. If not, the chuck is suspect.

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        • #5
          The flat tip helps keep it on center for a cylinder, so that's not a problem.

          It sounds like the jaws have something on them that is keeping the bar from being held securely. Either that or the bearings have a problem.

          Dan
          At the end of the project, there is a profound difference between spare parts and extra parts.

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          • #6
            The flat tip is hardened so it will glide over imperfections and provide a smoother indicator needle movement. At least that's the idea anyway. I'm calculating misalignment from the differential measurement from the average run out close to the chuck and at the end of the test bar. I don't have a ball tip to install on the indicator but I do have a mushroom head I could try. Thanks for the input.

            Ron

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            • #7
              Is the indicator plunger sticking?
              I had the same problem with my Mitutoyo Indicator, and I soaked the plunger with alcohol, and ran it in & out a few times to clean it out.
              Coolant, oil, and gunk can gum-up those indicators real easily.
              .
              I also noticed in your picture that you're clamping your mag-base onto the plunger area.
              How tight are you crimping down on that area?
              That may be squeezing the plunger as it moves in & out.
              It might help if you used the lug back, instead of clamping down on the plunger area.
              Last edited by KiddZimaHater; 03-19-2013, 10:43 PM.

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              • #8
                I've flicked the bar side to side and up and down with the indicator set and it always comes back to where I set it. I've also rotated the chuck and flicked the bar and the indicator comes right back to where it was set. I hadn't thought about bearings because it runs smooth and fairly quiet. Thanks for the tips.

                Ron

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                • #9
                  The indicator is relatively new and moves smooth and free. Yes, I'm clamped onto the barrel but not tight enough to cause a problem and the indicator operates smoothly through it's 1" travel.

                  Ron

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                  • #10
                    Might be an idea to make up a bracket to hold the indicator in your QCT and not use the mag base. Worth a try.
                    bollie7

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                    • #11
                      x2 on clamping the plunger. had that problem and changed my setup.

                      have you tried using the same setup on a flat surface and indicate that same surface. just push the mag base around.
                      Rob

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                      • #12
                        Are your spindle bearings rolling element or plain? A periodic repeat like you describe is probably rolling element bearing error. The rollers go around half as fast as the spindle, adding and cancelling runout in an alternating pattern. If you have plain bearings then scratch this thought.

                        My Sheldon does this and I am convinced it is bearing error.

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                        • #13
                          Your setup is probably fine- the results you are seeing simply have to be interpreted correctly. It's telling you a story and you have to figure out what it is.

                          It should be straightforward to determine whether the indicator is moving around and altering the reading. When you rotate the spindle, you are doing nothing to disturb the indicator mounting since nothing should be changing there. The only thing I can see happening is if the rotation of the leadscrew is somehow pushing or pulling on something attached to the carriage. Get that possibility out of the way first.

                          Then you can eliminate any effects from relative motion between fixed parts- the headstock would be my next concern. Without rotating the spindle, try to flex the headstock around and see whether you have more than one rest position on the indicator. Eliminating that, next put a bar through the spindle from the left end and see if there's more than one rest position for the spindle in the horizontal plane. If you haven't shown up anything obvious by now, next try to alter the position of the chuck in the horizontal plane by trying to bend it side to side, still in the horizontal plane. Avoid touching the jaws while doing this. This will tell you if the chuck has a good seating on the spindle. Then you go to the test bar- push it back and forth to see if there's more than one 'home' position indicated for it. That will tell you if the jaws are able to keep the bar from moving relative to the chuck body.

                          So far, all this has been done without rotating the spindle. You can expect a periodic error from the runout, and this should be repeatable exactly in the same places over one full turn. Every subsequent turn should repeat this pattern exactly. If this doesn't happen, then the problem is in the spindle bearing area. Now it breaks down into separate areas again- depending on what kind of bearing is involved. There could be play between the spindle and the bearing, between the bearing and the seat in the bore, and inside the bearing itself. Etc-
                          I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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                          • #14
                            Stokersix and darryl I think you guys called it. I've never heard of rolling element error but it appears that's what is going on. See my head stock drawing to verify that I do have rolling element bearings. Thanks again.

                            Ron

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                            • #15
                              Rolling element error- now why is there so much error? From your description it would seem that the errors are in the range of 10 thou or more. That's horrible, beyond acceptable even for a clothesline pulley. Well, maybe not for a clothesline pulley, but way more than exhibited by even a crude off-shore ball bearing. Something is definitely wrong here. Two tapered rolling element bearings in preload should have virtually zero runout- down in the low tenths at least, and I'd suggest that more than two tenths would be a large error here.

                              It almost seems like the bearings are contaminated, or there's a loss of pre-load - perhaps a bad rear bearing allowing the spindle to wobble at that end-

                              To me it looks like you have a new project at hand- rejuvenating the spindle on that lathe. If there is indeed that much change in the spindle position at it's rotating, fixing it will transform the lathe into something much better than it is now.
                              I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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