4 jaw chuck
I wish I had learned this years ago.
I have been avoiding my 4 jaw because it seemed to take hours to center a part. Then recently I saw a picture of someone using 2 keys at once.
That makes it really, really easy. You can feel the pressure on the part while watching the gage dial. Now its a a 2 minute job!
I guess the pros feel this technique is obvious, and I suppose it is, so they didn't bother to share. Or maybe to keep a beginner like me a beginner.
Sorry, as a "pro" I have never ever seen 2 keys being used to centre a 4 jaw. Believe me 1 key is plenty and the more practice you get the faster you become.
You might also want to 'map' your scrolls, Ie, see exactly how much movement one rotation is. I found I was way overturning and hence overshooting while dialing. Iv let my friend try once or twice and he did the same thing. Iv found it goes much quicker if you undershoot then overshoot.
Remember that 0.1" of jaw movement alters TIR 0.2", And the screws in chucks are very coarse, Often 10TPI or less (0.1" per turn), So 0.05" TIR for example might be as little as 1/8 to 1/4" turn of the chuck key to fix.
I can dial things in to 0.001" TIR at one distance from chuck (Cough...) within 1 min with just one chuck key now.
One of the big tricks is below about 0.02", you no longer fully loosen the low jaw, but loose it, and tighten it lightly, then tighten the high jaw firmly.
At 0.005" You basicly just tighten the high jaw and leave the low jaw alone, unless its allready *very* tight (As in, too tight to make any tighter), And then you just loosen it, and retighten moderately
At 0.001" you just go around the chuck and tighten each jaw slightly each revolution untill its desireabley tight for turning, maybe putting a little more force on the jaw thats 0.001 high, but you'll likey overshoot it anyway.
Last edited by Black_Moons; 01-27-2011 at 01:54 PM.
I can't say if it's 'pro' or not, but I can see no reason why I would rather use one than two. If it's non-critical I can have it centered in a couple of moves. Set zero. One to the opposite side to get the offset, dial out half with the opposed keys... takes a second, swing 90 degrees and dial out all the error... takes another second. Generally it will then be running at about 0.002 TIR. Then I can get more fussy if needed.
It certainly can be done with one key but they are not hard to make so why do that?
agreed, haven't seen it done with two nor do i remember seeing a lathe set up with two keys the same size. One hand moving the chuck, on with the key....should take no more than a minute or two max. Practice does make perfect....but if it's taking hours, heck if its taking 5 minutes, there is definitely something off in your method. Describe how you're going at it and maybe we can fix things up.
Originally Posted by Tony Pratt
2 keys ?
I have enough trouble keeping up with one having one in each hand would confuse me big time
I have been using a four jaw for many years and have never seen anyone use two keys or even tried it myself. It's to easy using just one key to try using two keys. Many times I use a break over bar instead of the chuck wrench. I have made a few adapters to fit the chuck screw.
My method of centering the jaws to put the work in takes a lot of the centering problem out.
It's only ink and paper
Amay, I use the two method but they are probably like you saw in that they are not two T-handle keys like normally used to tighten chuck jaws but two small short keys with knobs that fit in palm of hand. Use regular chuck key for final tightening. Nothing wrong with either method but prefer method you stated. Maybe I like the method maybe because I'm not a pro. gary
Sounds like someone is trying to make adjusting a 4-jaw more difficult than it really is.
Their next great idea will be adding chuck keys to a welding clamp so you can turn opposing screws at the same time, loosening one and tightening the other. How cool would that be?
I'm a pro of many years experience but I remember my learning days as an apprentice. Ehrn my classmates and I rotated through the lathe sections, we were given the oldest most decrepit four jaw chucks. We weren't allowed to use collets, three jaws or any other spindle tooling until we were quick and efficient on the old junk as tested against the clock.
Dialing work in a worn-out 4 jaw took forever and it was agony to endure and the next door mechanics assigned to look out for us were not sympathetic to our complaints. They expected one thing: round work centered to 0.001" or better and a good average if the work was out of round. We were allowed about three minutes from open chuck to dialed in before the nagging and criticism started. No exceptions. It wan't harsh or arbitrary; we were given hints and encouragement.
In about a week or so, most of us experienced a break-through. The information our teachers pounded in our heads finally came together. We never swallow the work in the chuck; we just used the first two serrations of the jaws. We worked opposite jaws in pairs. We never turned the spindle more than 1/2 revolution. We knew just how much to move for each adjustment. We never slacked the jaws too much so the work fell out. We placed pads and protected work from the jaws almost automatically. We dialed in next to the chuck then bumped the overhang around to dial the long axis in. Back and forth a few times until a pump sleeve was zero-zero, both ends and its wasn't squashed out of round by the jaws.
In that week all of us passed the test: we dialed in a valve body from the floor to centered in the lathe in 2 minutes by the clock. Since then (about 1963) I've trained hundreds of apprentices, operators, helpers, kids, old farts, men and women, boys and girls, Baptists and Buddists, rich and poor, etc how to work with four jaw chucks. Never takes more then ten minutes of teaching and a couple of hours of supervised practice to get the moves down. Thereafter it's practice.
Two keys or one, I don't care what training wheels you use. If I had my way, I'd remove all the noob's chucking equipment from their shops leaving only the four jaw. Then I'd give them the Lesson, tell them to practice, and dissappear for a couple of months. Then I'd come back with their three jaw, collets, etc and chances are the noob would not sieze it as though he were drowning and I threw a life line.
Nope, he would be competent on a four jaw and working with it has become automatic and natural. No chucking problem would be beyond him. The other spindle equipment would merely be a little more convenient and efficient for some classes of work - which is as it should be.
Last edited by Forrest Addy; 01-28-2011 at 07:48 AM.