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Extending a motor shaft

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  • #16
    Originally posted by Bob Engelhardt View Post

    I had never considered its shelf life until I had a red and a blue thread lockers go bad. They were probably 5 years old and 95% unused. Really annoying to throw out so much unused product. I replaced them with much smaller sizes.
    I am shocked. 5 years? Did Loctite change their formula to shorten the shelf life?
    Location: Saskatoon, Saskatchewan, Canada

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    • #17
      There is a world of different tapers. Fast tapers would be little use, they would push right off from side pressure. Very shallow (locking) tapers would wedge on tightly and be hard to ever remove. But that may not be a bad thing.

      An intermediate taper, not quite self-locking, would be the best. And, yes, certainly a retaining bolt, even an MT or B&S taper wants a bolt to hold in the arbor.

      Something you do have a reamer for tends to sound good, although that would force you to match tapers, which is more fuss.

      Just do not move the compound between cutting the male taper and boring the socket. You can then choose any taper in the wide world to use.
      CNC machines only go through the motions.

      Ideas expressed may be mine, or from anyone else in the universe.
      Not responsible for clerical errors. Or those made by lay people either.
      Number formats and units may be chosen at random depending on what day it is.
      I reserve the right to use a number system with any integer base without prior notice.
      Generalizations are understood to be "often" true, but not true in every case.

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      • #18
        Originally posted by Bob Engelhardt View Post
        ...
        I have some LocTite 609, 660, and 680 retaining compounds. The 609 ...[has shear psi such that] torque limit would be 150 ft-lbs (203 N-m)! I do need to test that it hasn't timed out (exceeded its shelf life).
        I did the LocTite test: a 1/2" rod in a 1/2" plate took 30 ft-lbs to break. Works out to 1800 psi shear (2300 psi spec). It has an expiration of 2006. So, 22% loss in 14 years. I can live with that.

        My shaft extension will have a 1/2" shaft in a 1" long extension - 60 ft-lbs yield. More than good enough - the motor is rated at 1.9Nm (1.4 ft-lbs) at speed. At stall it will be considerably more, probably not 40x. I hope.

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        • #19
          I would like to add a comment to J Tiers taper recommendation in post #17. Make absolutely certain that the tool height of both external and internal tools are exactly on the centreline, or the tapers will not match even if the compound is not moved.

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          • #20
            Way back when I did a lot of taper turning on the Unimat- mostly for fun. Tool height being exactly on center is a good reminder.

            In my case, the headstock rotated to allow this, while the tool rode only left and right, not at any compound angle. The hard part was duplicating the rotated angle to allow boring a matching taper. The Unimat had a pin that would align the headstock for normal turning, but only rough markings for other angles. Straight turning was a bit of a task, as the pin would need some play in order to insert it, and that play could have your headstock alignment off by some unknown amount, and I'd have to do some testing to see when I got it right. I ended up making a tapered cutter and a matching tapered pin to eliminate this problem.

            I've gone off topic of course- back to the original problem now. Has a decision been made as to how to do the shaft extension?
            I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-

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            • #21
              On-center is a requirement anyway, if you expect to get a usable taper.

              If you use the compound, you should be able to use it for both ID and OD at same setting, but you obviously change tools between the two.
              CNC machines only go through the motions.

              Ideas expressed may be mine, or from anyone else in the universe.
              Not responsible for clerical errors. Or those made by lay people either.
              Number formats and units may be chosen at random depending on what day it is.
              I reserve the right to use a number system with any integer base without prior notice.
              Generalizations are understood to be "often" true, but not true in every case.

              Comment


              • #22
                Follow up: I kept it simple and made a 5/8 extension bored 1/2 to fit over the shaft. Loctite-ed for remove-ability. Cutting a key way was a problem: a 3" cutter on my horizontal mill would hit the armature winding before the key way was long enough. Finished it (badly) with a carbide burr and file. Next time I'll cut the key way before Loctite-ing

                As careful as I tried to be, the result had 0.009 TIR. Ugh! I fixed that by grinding in place:
                Click image for larger version  Name:	IMG_E1981.JPG Views:	2 Size:	1.79 MB ID:	1917999

                Of course the shaft is no longer 5/8, but the runout is now 0.0002-3. Next time I'll make it oversize and grind to size.
                Last edited by Bob Engelhardt; 12-25-2020, 11:15 AM.

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