Finally I managed to get a half big grinder for chips on the local fleamarket.
I have no idea what machine it could be but probably some 1.5 - 2.3 kW model.
I made a little "plan" in Paint about mating it together with the motor.
My concerns:
The small cog was originally put on the shaft of the grinder only by the friction force what a well tightened nut gave to it. Withouth machining tools I'm a bit reluctant to try to create an insert for the motor shaft to use the same solution.
The idea: I cut a little, 4mm wide, 4mm deep slot on the motor's shaft which is 18.8mm in diameter. Also I cut out a fitting piece from the bottom of the cog, so they will sit together and this joint will transfer the torque.
the motor output shaft has a hole drilled into it, some 11mm in diameter, with tiny teeth inside. The cog has a bore inside of 10mm diameter, so what I thought is that I have a 10mm steel bolt (I happen to have one already cut) which I could fit into the hole on the motor shaft using some soft metal ring and loctite. This would center the cog perfectly and the thread on the end would keep the cog escaping. Hopefully.
What I have problem with with this two joints is: I have no idea how strong they will be...
anyone with some mechanics - machining knowledge could give me a hend here?
