Several days ago I started work on the boiler for the model steam shovel. It needed to be 5" diameter to be scale size, and I was able to find a piece of 5" seamless tubing down at the plant where I use to work. Real good stuff. Only the wall was so thick it about broke my arm to pick it up. It would probably withstand several thousand pounds per square inch internal pressure which was also a bit more than I needed, so I decided to bore it out until I had a more reasonable wall thickness and get rid of some of the weight. My standard steady rest would not accommodate the 5" diameter so I rigged up a Rube Goldberg type steady rest from some pieces of flat bar stock that was laying around. I did not even cut the pieces to length. For contact supports I used skate board bearings. (Those kids will learn not to leave their skate boards laying around unattended)
The bottom ends of the bars are bolted to a 3/4" plate that is clamped to the bed, but as you can see the upper ends are just clamped together with some sturdy C-clamps. The boring bar was only long enough to reach half way through, and when this picture was taken one end had already been bored out and the boiler tube flipped end for end and a couple passes had been made in the second end. The whole operation went very smoothly from start to finish, and the thing has been tore down and put back on the metals rack.
It is such a simple thing that I hesitate even posting it, but perhaps someone will pick up and idea that they can use sometime.