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I'm trying to stick a very delicate plastic second hand, salvaged from a clock, to the metal spindle of a stepper motor.

I have tried a couple of types of epoxy, pictured (and left for the entire cure time, not just the set time) but it did not hold. I can't really apply any pressure at all to the bond. I'm scared to use superglue as it's too liquid and I'm afraid it'll get into the motor and ruin it.

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4 Answers 4

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Put a nice big glob of hot glue (glue gun type) on the end of the gear and press the hand into it. You want enough hot glue that some gets onto the gear teeth to help hold better. A slit piece of scrap paper (or two with the slits in different directions) would catch any excess if you used too much, and it's easily trimmed away from the gear when cold if you used too much.

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Attach the pointer to a short piece of tubing that fits snugly onto the stepper shaft.

Something like a drinking straw could work, or a piece of a ballpoint pen, or toothpaste cap, or toothpaste tube end.

You could put a piece of wood dowel inside the tubing and use a tiny screw to attach the pointer to the tubing.

Alternately, you could drill a small hole through the tube and insert a thin rod, such as a ballpoint pen refill.

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With a small piece of masking tape cover the mounting hole of the second hand. With a small wire (or needle) probe pack the tape into the mounting opening. Test for fit.

You may need to push the fill tape in a few more times before there is enough to hold the dial in place.

It may be simplest to purchase a proper fitting part.

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Heat the second hand with a heat gun then press the hot plastic onto the metal spindle. Obviously, you'll want some sort of insulation between you and the hot plastic so you don't burn your fingers - use a piece of wood or similar to apply even pressure. You may want to drill a hole just larger than the size of the spindle through your wood. This will allow you to see exactly where you're pressing and allow the wood to push past the top of the spindle so you can move the plastic to the desired height on the spindle.

You may want to drill a hole in the plastic, a bit smaller than the diameter of the spindle, as a starter. That way, when you push, you're only pushing a bit of plastic out of the way, not trying to make the hole in the fist place.

As the plastic deforms around the metal, then cools, it should shape itself exactly to the spindle and key into any key ways, splines or other shapes on the output shaft and hold itself quite nicely. If necessary, add a small drop of epoxy on top of the second hand to hold it to the shaft after the plastic has cooled.

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