So I bought some goodies on ebay, including a 4” 3 jaw lathe chuck with an R8 adaptor to use in my Bridgeport. Well, the retarded chimp that I bought the stuff from (I’m temporarily withholding names till I see if he makes any real effort to fix things otherwise, I kind of doubt it based on my experience with him/the company so far) took everything, chucked it in a flat rate USPS box with no padding between individual boxes/items to keep them from moving, opened the 4” lathe box, took the top foam packaging/padding out of it, bolted the R8 adaptor on it crooked, left the packaging out and folded the box flaps around the R8 stem which smashed the rest of the contents in the box in the process of getting to me. (the outside box got to me fine with no significant marks on it, but everything inside it is mangled, even the chuck box ended up with a big hole in the side of it and all it’s parts were scattered around the inside of the USPS box)
Anyway, first I put it in my bridgeport and checked it with a dial indicator- it’s .047” out… grrr… I can actually see daylight between one side of the adaptor and the back of the chuck, and not the other.
I took and loosened the mounting screws from the backing plate/adaptor to the chuck and carefully tapped it loose, cleaned up the burrs made whoever slapped this thing together, cleaned everything , made sure the mounting faces were as good as they were going to get and put it back together (and noted that either that either the treaded holes in the back of the chuck or the holes in the adaptor plate are miss drilled, and when you line one up the other 2 are a little off, also one of the recessed holes in the adaptor piece is not drilled as deep as the others so one of the allen cap screws sticks out a little). Anyway, I went back to the Bridgeport and dial indicator:
Measured at the R8 adaptor flange: less than .001” runout, the needle just barely wiggles as it goes around.
Measured at the machined side of the chuck, about 2/3 of the way down, between the adjusting head and the grooves that the jaws ride in: right around .004” runout
I chucked up a polished steel round that I know is pretty good and chucked it up and loosened and did it again 3x (and then had to go to work) and got:.007”, .004”, and .004”
(I don’ t know what the deal was with the one .007” reading, it shouldn’t have been dirt, I’m hoping that it’s not a sign that the jaws aren’t repeatable …)
So I know that part of the answer here is “well, how accurate do you need it to be?” but realistically, how accurate can I expect average new parts like this to be out of the box? I was hoping for better than .002”, but I don’t know if that’s really realistic.