Calibrate / Adjust Starrett Digi-Chek 258 Height Gage
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  1. #1
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    Default Calibrate / Adjust Starrett Digi-Chek 258 Height Gage

    I picked up a Starrett Digi-Chek 258 height gage that's waaaay out of calibration. Someone must have messed with it and that probably explains why it was sold so inexpensively. I missed the burrs on the four slot screw holding the top of the micrometer barrel, a sure sign that somebody's done something. Be that as it may. It's out of adjustment.
    The bottom of the stack rests on the top of the surface plate long before I can lower the 1" step to match a 1" gage block. I assume this gage cannot actually give a 1.0000'' reading and starts at somewhere over 1". Is that correct?

    I'm assuming you'd have to set the calibration with a 2" gage block, so here are the readings when the 2" step is zeroed on a 2" gage block. The digits read .008 and the micrometer top reads .9622
    04-step-zeroed-2-large-.jpg 05-reading-when-zeroed-2-gage-block-008-.9871-large-.jpg

    I'd like to hear from someone who's more familiar with these than I am even if it's a Cadillac or a Mitutoyo or some other similar gage. I can spot two areas that might be places for adjustment. The feet are screwed into the base. They're currently bottomed out in their holes, so would only serve if the gage stack needed to be raised. My guess is that these are not for calibration, but only to adjust squareness of the gage. There also may be an adjustment on the rear of the stack where it attaches to the micrometer stem as seen in the photo below. I'll probably also need to get to the area with the digital mechanism but haven't carefully looked for ways to do that yet. How do you adjust these? By any chance does someone actually have a parts breakdown?
    06-base-possible-adjustment-screws-large-.jpg07-upper-connection-gage-stack-large-.jpg

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    Can't help you on the actual adjustments for calibration, but I'm glad you didn't pay a lot for that poor thing, it's not been well cared for. On the feet, I agree that if the device is square you don't want to mess with them, but I wonder if they're OEM or if they were someone's idea of a fix. Poorly finished bolt heads aren't what I'd expect from a Starrett precision reference, the units I have use lapped carbide pads for surface plate contact.

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    Quote Originally Posted by Milland View Post
    Poorly finished bolt heads aren't what I'd expect from a Starrett precision reference, the units I have use lapped carbide pads for surface plate contact.
    It apparently is the way they're all made. Here's a photo of the base of one on eBay showing similar hex headed feet, and there is yellow paint like that on the column on the sides of my hex / bolt heads, so they're probably original.
    06b-base-digi-chek-ebay.jpg

    Do your height gages go as low as 1.0000" or do they contact the surface plate before that? Of course yours might be constructed differently.

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    These pics are not great shots, but my Mitutoyo 515-311 goes down to ~.2000" with a little foot, and I think that's the limit before it hits the plate. It does use carbide pads for contact, held in with ctsk flathead screws. I had another device I scrapped which also used carbide contact pads, those I kept for other potential uses.

    This Mits unit came out of Hughes Santa Barbara Research, through some other hands, then to me. It's a pricey little guy new, but fortunately I got it in good shape and at a decent cost. Funny how they even polished the bottom of the contact stack, you can see the camera reflected in it. pb200002.jpgpb200005.jpg

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    This model the stack does not bottom out on the plate.
    Normally the factory finish is a matte black krinkle paint and the feet are lapped to a mirror finish, suspect yours has been modified sometime after it left Athol.

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    Quote Originally Posted by Colt45 View Post
    This model the stack does not bottom out on the plate.
    Normally the factory finish is a matte black krinkle paint and the feet are lapped to a mirror finish, suspect yours has been modified sometime after it left Athol.
    How low can it read? Clearly the instrument has been fooled with, but the feet are shinier than they appear in the photo and may have been lapped.

    Milland. Thanks for the photos of your Mitutoyo.

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    Quote Originally Posted by RLamparter View Post
    Milland. Thanks for the photos of your Mitutoyo.
    No problem. Let us know how you do with getting the device working correctly. You might just call Starrett in Athol, MA on Monday, I understand they can be helpful over the phone.

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    The rear foot is not the original, but the front two are. These are normally screwed in tight, and the block stack/base parallelism is adjusted by lapping the feet. The nut shown in your 4th picture is used to raise/lower the stack until its height agrees with the micrometer.

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    Quote Originally Posted by RLamparter View Post
    How low can it read? Clearly the instrument has been fooled with, but the feet are shinier than they appear in the photo and may have been lapped.
    The bottom gage block rests on a small bracket (which is attached to the main column screw), approx .125" thick, that prevents being able to zero on the plate and read 1".

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    The suggestion to phone Starrett was a good one. They answer their phone with a live person who directed me to their Weber Gage Division. They sent me an instruction sheet / owners manual, a parts breakdown, and a zeroing procedure sheet. If I can attach them to this message, I'll upload them since they may be useful to other readers in the future.

    Well..... Although the "manage files" button says that PM accepts pdf's, they wouldn't attach to this post. I've uploaded them to the Metalworking Dropbox http://www.mwdropbox.com/ All of the files I uploaded begin with "Starrett Digi-Check 12-258" so unless the site owner changes / shortens the name, use that name at the search function located here to find them:
    http://www.mwdropbox.com/dropboxsearch.html

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    Quote Originally Posted by Colt45 View Post
    This model the stack does not bottom out on the plate.
    Normally the factory finish is a matte black krinkle paint and the feet are lapped to a mirror finish, suspect yours has been modified sometime after it left Athol.
    The paint looks original; it's yellow krinkle paint and it's inside the frame where I'd expect to see it. I'm pretty sure the feet are original although the rear foot is a little more scratched than the two front feet. This is so far out of zero that somebody has messed with it. My instrument does not entirely match the parts diagram Starrett sent me so I suspect that this is an early model.

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    Quote Originally Posted by Colt45 View Post
    The bottom gage block rests on a small bracket (which is attached to the main column screw), approx .125" thick, that prevents being able to zero on the plate and read 1".
    OK. Mine sits about .125 off the surface plate too. The thought I had intended, but conveyed poorly is that the top of the bottom block never gets to 1'' off the surface plate. The top of mine only gets to about 1.125 because of the bracket below it. It could only provide a 1'' reading if the bottom block were about 1/8 shorter than 1''. Does the top of your bottom block go down to 1'' or only to about 1.125?

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    I've gotten some help off line by someone from another message board. The instrument is intended to read as low as .100 from the step at the bottom of the stack. When the micrometer is raised to .0000 that step should be 1.0000 high. Knowing that and confirming from the Starrett literature that the adjustment / zeroing nut is at the top of the stack was a major step forward. I set the micrometer to read .100 and adjusted the lower step to be on .1000, using a gage block for comparison. More info in another post when I have more time.

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    First I set the bottom step to be .1000 using a gage block. I donít have a .1000 gage block so I used a .1001 block and adjusted the test indicator to read zero at .1000.
    17-low-step-set-0.1000-used-1.0001-block-calibration-large-.jpg

    The digits read 000 and the micrometer head read .0038. I didnít realize it at the time, but the micrometer was .100 below where it should have been.
    18-digits-000-micrometer-.1038-when-step-.1000-large-.jpg

    I next moved the stack to a 1.0000Ē height compared to a gage block.
    19-step-raised-1.0000-large-.jpg

    The digits showed what appeared to be 000 and the micrometer head showed .9788. After awhile I realized that what appeared to be two zeros were really digits with part of them missing. The top one for sure was a .9 but the middle one was uncertain, possibly an 8.
    20-digits-000-micrometer-reading-.9788-when-raised-1.0000-large-.jpg21-micrometer-reading-.9788-when-adjusted-1.0-gage-block-large-.jpg

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    Confused by this, I raised the micrometer to read 0.000, which is the 1.000 height setting and noted that the digits read .011
    22-micrometer-set-read-1.0000-digits-reading-.011-large-.jpg

    Then after loosening the small set screw that holds it in place, I used the ĹĒ nut at the top of the stack to adjust the stack height to be even with a 1.0000 gage block.
    07-adjusting-mechanism-top-stack-annotated-large-.jpg23-step-adjusted-1.0000-large-.jpg

    Then I lowered the micrometer to read .1000 and checked it against a gage block. The digits read .111. Clearly the digits were off by .011
    24-micrometer-lowered-0.1000-digits-reading-111-large-.jpg25-step-checked-against-.1000-gage-block-after-stack-adjusted-large-.jpg

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    Knowing that the counter was off and that some digits needed to be repainted, I set about to access the digital counter. To get to this I had to remove the entire head. The micrometer partially covers the four socket screws holding the head on, so I had to release the micrometer first in order to reach them. The micrometer is held in place by a locking screw accessed via a hole in the right side of the head. As soon as this is loosened, the stack pushed the micrometer up.
    27-micrometer-clamp-screw-loosened-releasing-micrometer-large-.jpg 28-loosening-socket-screws-remove-head-large-.jpg

    In order to free the micrometer from the stack, I loosened the set screw holding the connector between the micrometer head and top of the stack. Itís tight but you can pull directly up, pulling the connector off of the stack. In retrospect, I might have been able to slide the micrometer shaft out of the connector since itís a slotted connector as seen in the photo below.
    26-loosening-set-screw-allow-disconnection-micrometer-stack-large-.jpg 07-adjusting-mechanism-top-stack-connector-cropped-large-.jpg 26b-connector-stack-micrometer-cropped-large-.jpg

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    The micrometer turns the counter via a keyway in its shaft that drives a key in the pulley connected to the counter
    32-spine-head-syncrhonizes-plastic-gear-head-large-.jpg

    With the micrometer out, I removed the three socket screws holding the counter mechanism in the head.
    30-bottom-head-annotated-large-.jpg

    The large pulley to the rear of the counter drives a small pulley at the bottom of the counter. Note the digits with missing parts.
    33-counter-removed-head-missing-parts-digits-lighter-large-.jpg

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    I bought a 5/0 artistís brush and a tube of white acrylic paint at Michaelís Craft Store to repaint the digits. It worked, but a thinner paint might have worked better. The paint did not flow off the brush as well as I would have liked and my hand wobbled a little as I remade the digits. When the paint was semi-dry (only a minute or two) I used a round pointed toothpick to scrape away some of the unevenness and reshape some of the digits. The end result was decent, but not entirely professional. I noted that the paint adjacent to the missing areas was quite brittle and lifted off occasionally, requiring filling a slightly bigger gap.
    35-paint-5-0-brush-used-repair-digits-large-.jpg 36-counter-set-.100-note-digits-repainted-large-.jpg

    When I reassembled the head, I set both the counter and the micrometer to be .100. I noticed a slight rotational mismatch in position of the pulley key and the micrometer keyway. The belt and the pulleys are toothed. I lifted the big pulley up and rotated it one tooth clockwise to better match the keyway in the micrometer shaft. I wasnít too difficult to lift the pulley out, but after moving it one tooth, I had to rotate the large pulley a few turns back and forth to get it to slide into position in the belt again. After this, I reset the counter to .100 and put the micrometer back into the head. It took a little wiggling to get the micrometer shaft into the pulley. My choice of one tooth on the belt was good and it appears that one tooth equals .010Ē on the counter.
    37-note-position-spline-larger-pulley-large-.jpg38-matching-zero-micrometer-location-spline-large-.jpg

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    I had to rotate the witness mark slightly clockwise in the head In order to keep the counter reading .100
    39-micrometer-back-head-matching-readings-large-.jpg

    I think that to set the witness mark to the center of the head with the digits still reading .100, Iíd have to remove the micrometer thimble, rotate the micrometerís witness mark to the center, then put the thimble back on in a position that matched what was showing on the counter. Itís obvious from the plier marks on the screw that holds the thimble on that someone had been here before and I suspect that thatís why the witness mark has to be off center currently. Iíve read that the thimble on hand held Starrett micrometers is held in place by a short taper, so Iím guessing this is probably the case for this too. My offline advisor has suggested that I make a puller/clamp to go under the knurling on the thimble and pull it off rather than trying to tap it loose which is done for the small micrometers. That may be a project for another day. Reassembly was the reverse of the disassembly. After reassembly I re-zeroed the stack using gage blocks and a dial test indicator.
    41-top-micrometer-buggered-screw-large-.jpg42-buggered-screw-cropped-large-.jpg

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    Good deal. Since you really got into it you won't need to make the puller. Now that you know how to take it apart and reassemble it; you just need to back the spindle all of the way out then you can seperate it from the thimble as though it is a regular mic.

    -Bob


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