I guess I havnt used a good three jaw chuck over the yrs. To get from
.0002 to 002 out of a 3 jaw. Cant say I have used one. For the most part, even when testing with a known good piece of material, Ive allways found .005 to .008 to be the general. Im not talkin about any hi end chucks here, just run of the mill chucks, and ones that have some mileage on them.
I have used a few set true chucks that get the run out down low, but if I have to play around with those, Id rather stick to the 4-jaw. I havnt ever found a 3 jaw over my life time that I could remove the work piece, and re chuck the part and not turn a step. And yes this is with marking the part to put it back in the same spot.
I dont think Id ever ask a 3- jaw to do accurate work, unless the job could be start to finish in a single chucking. Really, how often is that? The 3 jaw is fine for some stuff, but I would count on getting accurate parts on it alone. I have several 3 jaw chucks in my collection from 3-inch to 12 inch but when it comes to making accurate parts, the 4-jaw is the way to go.
I know, the 4-jaw takes a few mins to get it dialed in, and the 3- jaw is much quicker. The set true chucks can be dialed in , but for the time it takes, the 4 jaw will do the same thing, and have a better grip as well. The 4 jaw will get you down to .0002 easy.
I suppose it a matter of how accurate you want your parts. Over the yrs, I wont even use the 3 jaw on the rotary table. I perfer the ability of the the 4- jaw to dial the work piece in. Im not a big fan of 3 jaw chucks,,cant ya tell? The 4 jaw does seem to be a pain to set up for the first while, but you should force yourself to use one till you get good at it. Once that happens, those 3 jaw chucks will sit collecting dust. The ability to dial you work piece in to the absolute min run out will only make more accurate parts, and a better machinist out of you.
I've run some bar stock that was up to .002 eccentric. It would vary down the bar length.
