How to hold 3 inch alumimun tube in lathe

I use spiders on tubes also. Everything from 4 in. dia. To 18 in. They are pretty easy to make. Just a piece of round stock with 4 tapped holes in the OD, and center drilled. I back them up by sandwiching a chunk of wood between the spider an the chuck. Works good, but you have to be careful to balance safely holding the workpiece tight enough and deformation.
 
If you have some 1/4 inch alum plate, bolt 2 thicknesses together and center drill. Turn one side to the ID of your tube and the other to the OD. Stick it in the end of your tube and hold with a live center in your tailstock.
 
Also, I have bought some structural tubing from McMaster that was pretty far out of round and had asymetric wall thickness FYI.
Robert
 
The pipe is 3"dia,x1/2" wall x6": long, if it cant be securely held in a 3 jaw,I would say you have some serious taper in the jaws,and/or serious wear in the slots.....probably both.
 
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