Calibrate / Adjust Starrett Digi-Chek 258 Height Gage - Page 2
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  1. #21
    Join Date
    Oct 2008
    Central PA
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    The story continued. As noted in the previous post, the micrometer's witness mark wasn't centered, which bugged me. In addition, I discovered that I couldn’t get micrometer to go to the 1.1000 position because the top of the stack connector was striking the bottom of the head.

    The top of the micrometer's limit was a little beyond 1.050. I screwed in the micrometer .050 which gave clearance between the top of the stack's connector and the bottom of the head. At this point the micrometer was reading 1.000. I wanted to make this setting to be 1.1000, so I needed to remove the micrometer's thimble to reset its height. The thimble is held on with a screw having a flat top with four peripheral notches. I made a 'wrench' to fit this. As it turned out one of the notches was peened narrower than the rest. The previous owner appears to have used both pliers AND a punch on this screw. I tried tapping the offending proud area of metal in the notch with a small punch hoping to displace enough of it that the tool would fit, but better than that, it loosened the screw, which I removed by hand. After this was off, I filed the narrow notch until the tool fit.
    44-tool-w-prongs-next-nut-slots-large-.jpg 45-tool-slotted-screw-loose-i-lifted-mic-off-large-.jpg

    The micrometer's thimble came off with just a little shake exposing the tapered nut on which it sits inside the micrometer body.
    47-screw-removed-insides-micrometer-large-.jpg 48-closeup-insides-mic-blurry-large-.jpg

    I unscrewed the tapered nut until the micrometer was at a height of 1.1000, then I rezeroed the stack. I'd like to say that that was the end of it, but it turned out that when I checked measurements against gage block, they started to vary above 1.0500. This part of the micrometer threads must have been worn. I wound up lowering the micrometer stem a little more and raising the tapered nut a little more until I had measurements that checked from .1000 to 1.1000 I then reset the counter as previously described above and checked the readings with gage blocks at different heights before accepting it as done.

    A couple of extra things I noted along the way (ahem wasted time by making mistakes) Put the two front socket screws in the head before inserting the micrometer because the micrometer blocks these screws. Make sure the micrometer is fully seated in the head before tightening its holding screw. It may be easier to rezero at .1000 than at 1.0000 because the studs for the stack's return springs may interfere with the adjusting nut, depending on the position of the stack on the nut. When I lowered the mic to reset its height it bottomed on the surface plate before I got down to .1000 and of course had to adjust the stack height upward.

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