Buck Adjust Tru 6" 3 Jaw Chuck

D

dc10bill

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how does one "adjust true"? I know their is the 4 1/4" allen screw around the the 2nd part of chuck! When I screw on to spindle (Logan model 200 lathe) I get .023 run out on out side dia of chuck same as what I get when I chucked a 3/4" drill in to jaws! The lathe spindle has less than .0005 run out!

I took chuck apart to clean and lubricate I punch marked the 3 parts, the jaws are in their correct locations, the pads for the adjusting allen were installed at bottom of allens!
Turning the 4 allen adjusters in-out like one would do on a 4 jaw chuck, with chuck on spindle just doesn't do any thing in reducing the run-out! Totally befuddled,
 
You check the run out of the part that is clamped in the jaws of the chuck,not the run out on the outside diameter of the chuck. You use a dial indicator on the part that is held in the chuck,and keep adjusting those allen screws until the part runs dead true. You should be able to get the part to run true within .0005",unless it is not very round,such as a piece of hot rolled round steel bar.

There is not much adjustment range on that chuck. There is enough to get the part to run true.

When I want to check true running,I use the shank of an end mill. Most other things aren't really truly precision round.
 
You need to lightly tighten the chuck to the mounting plate, chuck up a known true round stock, and adjust the TIR the lowest applying even torque to all the Allen screws. Then fully tighten the chuck to the mounting plate, and then recheck the run-out. Rechuck the round stock or try other round stock and adjust if needed, your TIR should be under 0.0004" for most Set-True type of chucks in the 6-8" range. The bodies of my Set-True chucks are all out a few thousands, but at the jaws, they hold stock at better than 1/2 thousand.
 
Look at the video on YouTube video "Centering an Adjust-Tru chuck"
. He points out it's just a 3-jaw chuck mounted within a 4-jaw chuck.

Also: YouTube: Tubalcain 4 jaw chuck

He suggests using 2 keys. It's such a great way to go I'll never try any other method.
 
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