If you note on the James Crenshaw interview. The type tread mill he used being one part of his dog keep. It was not just free wheeling, but had some inherit drag to it and was a larger wide type mill. He let the dog work at it's pace with some faster out put.

The type Round table I built was on a positive traction truck rear end. All the Hog head gears and shafts were left intact. The dog could not just free wheel this extra big table. You fellas that have a wide enough building or lean two. Go twenty foot across. No harder to build one sixteen foot across as twenty foot across. The dog had to use all his muscles to keep it going. If the dog speed up the table did to amount of effort applied. If dog slowed down the table slowed to the amount of effort applied. It never over run the dog but ran at a constant rate to effort.

This was from my experience, the Round Table being the second best type mill to use. When bad weather set in and the Swing Jenny being the best, could not be used. I had a nice built slat mill from a mill maker that used those Volkswagen front end hubs and real professional skate wheel bearings. Was never crazy about a slat mill. I felt it could put to much stress on the back end and kidneys.

I did like Maurice said. It only cost a little more to go first class. I bought the best materials and put in a lot of thought on my Swing Jenny and Round table. I had a Cat mill that was 40 foot on both sides with hook ups to run the dog in either direction. The extra opposing 40 foot length on my Cat mill added inherit drag to it. So it was to some degree not free wheeling either. Overtime though I realized if the Cat Mill and Round table are built long and wide enough. One side for running will do. JMHO. Cheers