Shear Pin on a Central Machinery Mini-Mill

I recently found a set of metal gears that will fit my Mini-Mill. I
know the standard plastic gears will strip out if the Mill tooling is
pushed too far ( which I did once). I would like to put a shear pin in
the drive system and I wonder if any of you have done it? What kind of
shear pressure would be best?
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I suggest trial and error. Start with a small diameter AL. Run machine and see what it takes to break it. Use the data to estimate how much more strength you need.
Reply to
Karl Townsend
Or just settle on a pin that's too big and turn just the right sized grooves in it at the mating point(s) to form a weak point.
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Look at your gear train, cross section of pin should be less than the gear teeth or any other driving component. Diameter of the items connected by the pin has an effect.
It is one of those TLAR things if you can't do the calcs.
I'd go weak and work up. Grooves as mentioned fine tune things.
TLAR, That looks about right.
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Or perhaps calculate the shear strength of the gear teeth on the Nylon (or whatever it is) gears -- perhaps measuring with the remains of the failed gers), and then translate that to the shear strength at the hub/shaft interface diameter. Then bump it up in proportion for the metal gears -- unless you still have some plastic gears in the train somewhere.
I might consider something like annealed brass tubing as the shear pin to get a mild enough shear to protect the gears. (Or you could drill out enough of the ID of an aluminum pin to get the required strength.) Once you figure it out -- make a large stock of spares, and write down what you did to make those pins for future re-stocking.
Good Luck, DoN.
Reply to
DoN. Nichols

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