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  • bani chuck

    i took of this little chuck off a grinder. its nice and tight, it took me several minutes to get the gear back in (had to degrease it again), but there are some weird details. there are these two threaded holes opposite each other. the pinion was turning in one of them and the set screw was in the other. on top of that there was this "spacer" (?) that was lightly pressed in the bore with a corresponding hole, as if for lubrication. but there is nothing to lubricate.

    po butchered together the mt3 backplate and i wonder if he also produced the threaded holes. what for? the pinion shaft is 6 mm and the first half of the m8 thread it was running in is reduced to 6.9 mm. even in an original m8 thread it would have had 0.5 mm of play. can anybody make sence of this?

    and what do i do? thread in a bushing for the pinion or bore the hole out and press it in? and hope its in the correct location? how can i measure where it needs to be? i could make an exentric bushing, take prints and glue it in. but that looks like an advernture with an uncertain outcome. or press it down into the gear measure and add what, 0.05 mm?
    Attached Files
    Last edited by dian; 03-18-2021, 12:50 PM.

  • #2
    I don't understand quite what you are trying to do. Is the chuck going back on the grinder? The grubscrew and the threaded hole opposite the pinion hole are not original and seem to be for holding that bush in the chuck. The bush and grubscrew don't seem to have any purpose now and could probably be left out when re assembling. Perhaps it was a depth stop for a particular job? When you refer to the "pinion shaft", do you mean the screw which stops the pinion falling out of the chuck body? They are normally stepped and quite a loose fit in the groove in the pinion.
    Last edited by old mart; 03-18-2021, 02:35 PM.

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    • #3
      good idea on the screw locating the bushing. that didnt occur to me*. whatever i do with the chuck i want to get it operational. by pinion shaft im referring to the small stub (?) the pinion is supposed to rotate on. as it is now, its lose in the butcherd up thread and will need some kind of support (bushing). the question is if im missing something here, as it is incoceivable that po drilled out a previous 6.0 mm locating hole to 6.5 mm, threaded it to m8 and let the 6 mm "stubby-shaft" turn in it (which lead to it being chewed up). well, maybe he did do it to accomodate his set screw and then, for some reason decided to place it on the opposite side?

      anyway, im looking for ideas on how to repair the situation.

      i have come up with a new idea: plug the hole, make a punch with a heavy slip fit in the hole the large body of the pinion sits in and produce a mark on the plug to be enlarged to the 6 mm. this would require that the large hole has correct alingment, which might not be the case, as the pinion is loose in there and the parts were manuf. separately.

      *pretty absurd when it could be just pressed in.
      Last edited by dian; 03-19-2021, 03:41 AM.

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      • #4
        I don't see the reason for the bushing. It also appears, though this may not be true, that there's no way to access the setscrew once the chuck is assembled. This furthers the mystery-

        It appears that the tap used went too far and buggered up the bore for the pinion shaft. There was no reason for that- it just happened. But what if you turned the setscrew around and had it pointed out. Then on the mill you have a scrap mounted on the table. You make a dimple with a drill bit into the scrap, then that becomes a home for the point of the setscrew. You stand the piece like that and center the bruised bore using a custom turned piece in place of the drill bit. The piece is now standing vertical with the correct orientation and alignment for your corrective boring operation. Now you build around it so you can clamp it with that positioning, and change out the custom jig for a suitable boring tool.
        I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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        • #5
          Try not focusing on what is there
          and focus on what should be there.
          Stop being encumbered by legacy.

          -Doozer
          DZER

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          • #6
            If you were to fit the plate in the chuck body without the pinion, you would see whether the oversize hole was in line. Making or buying a bush that fits the pinion, (not too tightly) would allow the oversize hole to be enlarged for the bush to fit in. With the centre held in place with screws, a drill guide could be turned up to fit the chuck body and allow the hole to be drilled accurately in line for the bush.

            Don't let Doozers comments get to you, there are times when his comments are really helpful, but not every time.
            Last edited by old mart; 03-19-2021, 11:20 AM.

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            • #7
              so i decided to keep it simple and just threaded/lockited a m8/5.9mm bushing in there. it works well, but i consider myself lucky, because the two threaded holes are not even aligned. i rolled up some lead sheet and threded that into the other hole, thinking it would help balance a bit.

              nice little chuck, really tight.

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              • #8
                The pinion in a chuck only has to turn the scroll, so its perfect running is nowhere near as important as the other fits in the chuck. You got a good result, that is the most important thing.

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