This story is in many ways typical. My son bought a toy at a garage sale for 50 cents.
This toy is a extrusion device, it has a cylinder, a piston and a threaded rod/shaft that pushes the piston through the cylinder. It extrudes cookies or cream, shaped according to hole patterns on metal ends. A battery powered electric gearmotor turns the threaded shaft, pushes the plunger/piston, and extrudes dough.
This toy was missing the piston. I made it last night from a cutting board. Metal related aspect was that I made it using a boring head on a Bridgeport. The piston is round, 55mm in diameter, 8mm hole, and two4mm notches on opposing ends.
Anyway, closer to my question. The piston goes on the end of the threaded shaft, which is fitting snugly with the 8mm hole on the end of the shaft. Shaft gets thicker after that so it can push the piston with a "shoulder".
I believe that I also somehow need to fasten the plunger to the shaft so that it does not come off when it is pulled (as opposed to pushed) back.
So, my first thought is to just use a bolt or screw that goes axially into the shaft and holds the piston. My question is what kind of bolt/thread to use to hold in plastic.i