I have a chnc ii with a dunham collet closer. I trying just to get some rpm of of the machine but if I go much past 2000 rpm's the material just starts moving in the collet. I have had a .5 drill push back 1" hex aluminum feeding @ .003 if i drop the rpm to around 500 everything ok. I have a air bar feeder but limited on pusher sizes one in 1.5 and the other is 1". I figured if i ran the 1.5 on the 1" hex with no liner it should'nt be a problem. I have come to the conclusion that with out a liner that close to the material size I'am losing collet presure from bar whip. the only thing i could do is cut bars 25" long with a fitted liner in the head stock. I would be interested in finding out how the heck are people running these machines without having a but load of pushers of various sizes. I would like to run six foot bars and run a pusher no smaller than .5 although the feeder tube is over 15' long and I may just cut the thing down. I have ran other cnc's where the bar and the liner were not that close ie 1/4 round with a 1/2" liner. The only dif would be hydraulic collet closer. What i was thinking of doing is is using my 1" feeder tube and making a rod that can interchange with the piston. The feeder rod i use now has a cup that will rotate but how the heck can you do that with say a 1/2 rod no room for bearing of any size. The other thing i noticed is the closer does not seem to be true with the spindle without a liner and when i put a liner in seems to help. However i do still feel vibration coming thru the machine and have see it show up on the parts. I may have a combination of problems just not sure.