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Gear Slipping on Metal Rod

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  • Member since
    October, 2006
  • From: Western, MA
  • 7,388 posts
Posted by richg1998 on Sunday, November 05, 2017 11:34 AM

You could get a knurling tool from Micro Mark but expensive for one shot. Not sure how to do this in home workshop. There are some videos on you tube about knurling. I did this a few times when I was a machine mechanic but on a larger scale.

I would rough up the shaft and each side of the gear near the shaft location and use five minute epoxy.

Red loctite might work between the shaft and inside the gear hole as I believe it expands a little when setting. I remember pulling a couple bolts many years ago that red was used in.

Rich

N

  • Member since
    September, 2003
  • 4,137 posts
Posted by Overmod on Monday, November 13, 2017 9:17 AM

To put in some potentially helpful material that was only partially addressed in the ‘old’ thread:

”Real” Loctite is an anaerobic-curing material, meaning it will only set up if the joint is not exposed to oxygen.  An upset shaft may only produce this if it cuts corresponding ‘keyways’ in the gear, which may facilitate splitting, but the advantage is that it will not set up before the gear is actually pressed into the equivalent of perfect or interference fit.  

Cyanoacrylate cures by exposure to moisture.  That may be difficult to ensure in a tight joint.  As noted the basic crosslinked ‘result’ is brittle and may not bond effectively to some materials (and I do think some of the Delrins are in that category) ... more on that in a moment.

Epoxies are time-delay chemical cure, so are ideal for mechanical joining ... but depend on a relatively thick layer of bond for full strength, very different from the situation with regular CA.  For a shaft with gear you might want to open up some of the joint while keeping enough of the shaft OD and gear ID intact to preserve alignment in both ‘wobble’ and runout.

For shock loading, you want more of an elastic bond than an initially strong but brittle one.  Epoxies inherently provide this; I believe it is a characteristic of at least some Loctite.  I think the CA formulation that is loaded with tiny elastomer (rubber) particles is intended to provide elastic bond, and some of you with firsthand experience with it might comment.  Notably, the stretched-latex-membrane technique that reanimated this thread is inherently both self-locking and highly elastic without ‘bond failure’ at all in torque loading.

There are surface-activating techniques other than mechanical roughing that can be used for better bond strength; perhaps the most applicable here would be to use an ‘activator’ in the hole of an otherwise-slippery gear to enhance “bondability” there.  Has anyone here experimented with etching ‘primer’ for plastic pipe, or the ‘activator’ in one of those rear-view-mirror reattachment kits?

Now, the next fun thread will be about how to fix the situation when a gear does split...

  • Member since
    February, 2009
  • 329 posts
Posted by railandsail on Monday, November 13, 2017 8:20 PM

Piobond

What about this rubber based adhesive piobond??

  • Member since
    February, 2005
  • From: Vancouver Island, BC
  • 20,891 posts
Posted by selector on Monday, November 13, 2017 10:00 PM

It's "Pliobond", and it's too soft for that application.  Tim Warris, of Fasttracks fame, recommends it for affixing his laser-cut tie templates under his style of turnouts.

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    September, 2003
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Posted by Overmod on Wednesday, November 15, 2017 2:14 PM

Think of Pliobond as industrial-strength rubber cement.  It does not have the right characteristics for gear-on-shaft even if you get a reliable thin film on the two mating faces and press them together without twisting ... which you can’t.

Note that the ‘balloon trick’ referenced above is the equivalent of putting much better structured rubber molecules in the joint with the proper geometry to load them in compression without tensile separation on any part of the ‘bond line’ that finds itself loaded in tension...

  • Member since
    February, 2009
  • 329 posts
Posted by railandsail on Wednesday, November 15, 2017 6:03 PM

I was just always a fan of the rubber based adhesives due to their basic 'elasticity'

  • Member since
    September, 2003
  • 4,137 posts
Posted by Overmod on Wednesday, November 15, 2017 7:15 PM

When I was young, Pliobond was the best adhesive for strong resilient bond, or when some vibration damping was needed.  The only real drawback was the stink, and if you spilled it on anything stainable that was pretty much it. But my grandfather loved it for general repairs and so did I.

It’s just not good for smooth metal shaft slip-fit into a slick plastic gear, at least not without thinning and very extensive ‘drying’ time as it can’t be applied as contact adhesive for that fit.

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