Stepper motor pulley attachment

Discussion in 'The Projects Forum' started by JNBUK, Nov 18, 2012.

  1. JNBUK

    Thread Starter New Member

    Jun 4, 2012
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    I have a number of salvaged stepper motors from various electronics, the usual suspects; printer, scanners etc.

    I've just gotten past the prototyping stage in a project and I'm about ready to build it up for real but I have a fairly big problem.

    All the pulley sprockets seem to be press fit or some such, i.e. they are not attached with grub screws.

    Is there an easy way to remove them?

    I've seen similar things on automobiles where the sprocket is heated prior to application and shrinks on for a tight fit. I doubt that is easily reversible...

    However, if anyone knows anything more specific, please let me know!
     
  2. Cincinnati

    New Member

    Sep 28, 2008
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    If you know what it came out of, I'd contact that company. If not:

    Shrink fit is a common method to fit a metal parts together. I have never seen it used on plastic to metal.

    Is the pulley plastic?

    If so, I've seen several methods of connecting:

    1. locked onto the shaft with a set screw. Sometimes an epoxy is poured into the hole to seal it and prevent the screw from coming loose. Is there evidence of a hole that is filled in?

    2. It can also be locked on with a spring pin.

    3. Press fit, onto splined shaft, often with adhesive.

    4. Threaded with the opposite hand thread as the normal shaft rotation.

    You obviously don't have the fifth method —*It is easily identified: a split hub that is typically bolted together around the shaft.

    I don't know if I've been any help. If you still can't determine the mounting method, I'd start by boiling a pot of water and immersing only the sprocket in it for a few minutes. Then I'd try to work it back and forth to see if it will loosen. Leather gloves or other precaution against getting burned is advisable.
     
  3. JNBUK

    Thread Starter New Member

    Jun 4, 2012
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    0
    All the sprockets are metal on metal shafts.

    I see no signs of any threading, screws or adhesive so shrink fit looks most likely.

    I'll try some gentle encouragement with heating.
     
  4. mcgyvr

    AAC Fanatic!

    Oct 15, 2009
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    Just pull on them
     
  5. shortbus

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    Sep 30, 2009
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    The ones I have used, NEMA 23 size, had a very small (3/64" dia.) roll/spring pin through the pulley and shaft.
     
  6. djsfantasi

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    Apr 11, 2010
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  7. John P

    AAC Fanatic!

    Oct 14, 2008
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    It may be either a press fit or a loose fit with adhesive ("Loctite" or similar). Either way, you may be able to press the pulley off, but it's always awkward. You have to get some kind of bar under the pulley and bridge the bars across the jaws of a vise or similar setup, then tap the end of the shaft with a punch until the motor drops out. You shouldn't just pull against the motor, as it risks damaging the bearings.
     
  8. djsfantasi

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    Apr 11, 2010
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    That is exactly the function for which gear pullers are designed. The first link I provided is under $10 (US) including shipping.
     
    Last edited: Nov 20, 2012
  9. John P

    AAC Fanatic!

    Oct 14, 2008
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    Well yes--but when we "just have to have it now" we'll reach for some makeshift alternative. I've used this setup more than once and it has worked for me. If you can get the job done with what you have, it makes sense to avoid buying a tool that you never felt the need for before and most likely won't use again.
     
  10. Sensacell

    Well-Known Member

    Jun 19, 2012
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    If it was installed with Locktite, you will not get it off unless you "decompose" the adhesive by applying heat ~250 degrees F. for a while.

    That stuff is insanely strong in it's fully cured state, you will just mangle the parts otherwise.
     
  11. THE_RB

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    Feb 11, 2008
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    To the OP, how did you go trying gentle heating? Any success?
     
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