Turning rubber - yes!!!
Step 1: The Machine
Normal O-rings have a circular cross-section, but I needed some pieces with a square section. I knew from the past, that rubber can be easily formed with a grinding machine - there were only two difficulties: the cooling and giving an exact shape. This is not posible by holding the workpiece in your hand.
I have an old russian lathe and a little bit younger german (in reality: chinese) table grinding machine. So i have mounted them together, the grinding machine on the cross slide off the lathe. I have a diamond edge tool for correcting of the grinding stone: I mounted it in the lathe, and I moved the cross slide, while the grinding stone was rotating.
Step 2: The Holder
The holder has been made of a piece of steel - and in the same clamping, so the surfaces were absolutely correct. The end of the rod has a smaller diameter on which the rubber o ring seated well. The seat was made on the final size of the ring.
Step 3: The Process Itself
As the grinding machine works at a high speed, but reduced force, the O ring was sitting very good in it s place. i made atfirst one side, then I turned it with 180 degrees, made the other side too, after which as a last operation I finished the lateral surface.
The surface quality is VERY good, and the form also.
Step 4: Video
Step 5: The Original and the Square One
Of course normally in a good shop you can purchase a square O-ring too - but there are cases when you have no time, or you need a really special size.