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?

TIA,
DL

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?

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.

Karl

On Jul 20, 8:02*am, "Karl Townsend"
wrote:
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?

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.

Karl

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.

Dave

TwoGuns wrote:

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?

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.

Wes

TLAR, That looks about right.

On 2008-07-20, Karl Townsend wrote:


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?

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.

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.

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