Intro: Simple Merry-go-round (Drahdiradl)
This playground device is a rotating wheel on a vertical steel tube. Ropes are attached to the wheel, which are grabbed by children to spin around. The tube is fixed to the ground.
Step 1: Wheel Hub Assembly
Find a wheel hub assembly of a car and a (spare) wheel. If needed, find the flat breaking parts in between the two (breaking disk?) or anything as a spacer. Build a socket frame around it so both can be connected with decent screws. Make holes if needed in sufficient thick hub material. The parts should be connected with at least 3 points, distributed in a triangle around the middle. Weld the socket frame together and keep it short enough to reach it with the paintbrush from the inside later.
Direct welding instead of scewing doesn't seem reliable enough to me.
Step 2: Tube
Find a good zinc coated tube.
When connecting the socket frame to the tube, the rotating wheel plain must be 90° to the Tube, and it should be in the middle too. So consider making a auxiliary construction. That is, add two bars of 50cm around the future position of the tube. Place the wheel hub with the socket frame on a table with a fixed bar above. Weld a piece of sheet metal on top, so that you can draw a circle when spinning the hub. Cut the circumference of the future tube in the middle of this circle, like in the picture. Slide it on the tube and weld it together. Add 2 extra brackets to be sure.
Paint inside and out.
Step 3: Wheel
Add fasteners for the ropes, like this U shaped brackets from steel rope fasteners.
Step 4: Installation
Finally put it all together, fix the ropes with a sleeve or at least a knot that you can see from below. Put the thing in the ground 2m when it's 3m high or make a concrete founding. Have a check from time to time and have fun!