How to tighten a 3 jaw?

OK. newbie here and I have been getting a lot of answers to my many questions just looking searching and reading here. I looked up this subject just out of couriosity based on what my old man (Harold, who was a manual machinist/ tool and die man in the aero-space industry) told me many years ago before I had any interest in learning machining. We were just doing some random thing and when using one of his electirc drill motors and I hung up the bit and slipped the chuck on it. I caught a little heck for that... " what are you doing, your ruining MY drill chuck!" Being German there was one way to do things - his way. I was taught then to just snug it up with the first position, then tighten it up successively, around the chuck; 1,2,3 and 4. ending up going one past the first one used to initially snug things up with. He said that's the way he was doing things running his lathe at work and thats the way it should be done. So I've always done that... then more recently doing some real tho minor type stuff in the machine shop where I worked the guy helping and coaching me along told me the same, to use all three and go one more. I was a little surprised as I had heard from others use all three, and others saying it does not matter. Reading this there seems to be more controversy about than I would have thought but do the the Snug..1,2,3,4 method and it does seem to work well for me, now it's just a habit!
Just got the first reall cuts made on my new lathe and all is going pretty well.. and a retro thanks to all those have contributed here... there is so much good and useful information I ve not really needed to ask any serious questions as yet.
 
Must have missed this thread. I agree, there seems to be some controversy about how to tighten a 3 jaw chuck.

I actually queried Rohm once upon a time about this exact thing and was told that their chucks have a stated amount of run out that is only achieved when tightening a single pinion identified by the factory, which is marked. If you use any other pinion or multiple pinions then they do not guarantee the accuracy.

I have 2 Rohm 3 jaw chucks, one Yuasa and one Samchully. All have a single pinion marked and that is the one I use. It is interesting that when I used any other pinion or when using multiple pinions, TIR increased. So I guess the factory is right. What I also found is that cranking a lot of torque into the pinion increases run out, and using multiple pinions to get the chuck really cranked down increased run out the most ... at least for me. So, now I use the marked pinion and tighten it firmly and the chucks have never slipped.

I don't own cheap or worn chucks so I am not sure if the above holds in all cases. If I ever do own a chuck that isn't marked then I'll do as @higgite did and run my own tests, then mark the most accurate pinion myself.
 
+1 on what Mikey said. My chuck has the mark and I tested it once, seems using that marked one gives the least amount of runout.
 
xalky said:
I can dial in any of my lathe 3 jaw chucks to within .0005". Here's how I do it. I'm might catch flack for saying it, but don't knock it till you tried it!

I Chuck up the work piece and tighten all three scroll screws tight as if to hold the part for cutting. Now take a dial indicator and put it to the work piece and spin it by hand noting the run out. Now, take a brass hammer and wack the jaw that is farthest out. That's it. You might have to do it a couple of times to get it right. Works every time. This won't work if your jaw surfaces are out. I do it all the time when flipping a part around to get the concentricity as close as possible.

My speculation as to why this works, the scroll has some play in it, Particularly on older chucks. Giving it a good tap seems to move it just enough to get it right. Ironically, it doesn't move when working the part, and I usually push my speeds and feeds.

Marcel
Click to expand...

A variation on this technique was routinely used in the shop where I apprenticed and in the one I owned. First snug the part (not tight), indicate and tap the high jaw(s) with a soft hammer. Snug a little more, check and tap again. Repeat until you cannot tighten any further. Even a chuck with a badly worn or damaged scroll can be brought in quite close with this method. We rarely mounted a 4-jaw.
 
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