The most bizarre thing just happened 

Use a similar setup but with 4 bearings and you will get a hexagon 👍😋👊

Dennis! Try asking This Old Tony if he could help you out explaining what happens!

Having trouble fitting round pegs into square holes? No? Well don't worry, with Dennis' patented "Square-O-Matic" be assured if you are, you wont anymore!

hahahaahah i love that!!!! i was like WTF!! just as you said it lol

Nice video! Very interesting outcome.

The screw rod doesn't appear to be centred on the upper bearing. This would cause the two lower bearings to be applied with unequal force. It would be interesting if you could find a way to centralise the screw rod so that it applies pressure halfway between the two lower bearings (presumably in line with the upper bearing). A bit of angle grinder & welder re-alignment....or a different manufacturer of pipe cutter perhaps.

Get a copper cap and drill it out for a 1/8 inch pipe thread and screw and seal a threaded nipple and then solder it on to the pipe.

I think it has to do with the width of the spread in the two lower bearings.

Harmonics is your friend.

metal spinning is the technical term for what you want to do (I think) in your position I would take a hard wood dowel (oak, ash, hickory etc) dense plastic might work with an OD the same as the ID of the copper tube. turn the taper you want reduced a smidge to account for wall thickness at one end of the tube slip the dowel into the copper pipe mount the whole thing in your lathe, bring up the tailstock to prevent wobble. I don't know what speed to go at, but I suspect slow, use a fairly large stick of dense material with a rounded end to gently push the copper down onto the mandrel with a downwards dragging action. I know just the tiniest amount about metal spinning, in a previous job I assisted my boss trying to prototype something out of steel through metal spinning, but copper should be a lot easier, plus faster to anneal if needed.

In a way you did succeed in srinking it down.

The lower jaw starts chattering and seems to hammer it into shape. If you could make it so the jaw and bearings have no backlash then it might stop it from chattering. The transition on the edge of the bearings is likely too sharp. You might be able to get bigger bearing and turn a radius on the edge. I don't know if trying to do it on the end is harder than somewhere in the middle. You could cap the pipe, fill it with water, freeze it, and have a pipe that won't easily dent. The quick transition may be too sharp without some sort of mandrel set, but ice might work, especially if you can have a more gradual step down. Is there any way to use a bigger piece of flexible tubing that fits the copper pipe and adapt that to the smaller tube? Or perhaps get a copper pipe cap, drill a hole, jam in and JB Weld or something?

hahahahaha! awesome im crying

Just curious, why didnt you just leave the lower two rollers in the tool? Could you have also put two of your other rollers side by side in the upper jaw? Not that has anything to do with the weirs result. Any idea if the squareness happens in the same orientation on the tube? Is it possible that the way the original tube is formed you end up with four work-hardened lines running through it? Could those hardened lines be keeping the tube from collapsing along those lines? How much sense am I not making? ;-)

You basically broached it from the outside ? Due to vibration? Or something