Re: recommendation for 3 jaw chuck

Bill in OKC too

Maybe it's just because my first lathe I owned was an HF 7x10, but until I got a collet chuck for it, I took the cheap 3-jaw off, and put a slightly less cheap, much larger, 5" 4-jaw on it. Got so I could dial it in within 30 seconds or so. Helps to have a pair of chuck keys, so you can adjust both sides at once. That and some practice. I'm not a professional machinist, just an amateur. If I can get faster, you can get faster. I recently got a new-to-me (and still new, never been plugged in) Smithy CB-1220XL 3-in-1 machine with an 8" 4-jaw chuck and a 5" 3-jaw chuck. Got the machine more or less in position last night. My plan is to put the 4-jaw on it and leave it there. I expect to be using it while I'm refurbishing my Heavy 10L and I'm going to want the very best precision I can manage while doing so. 4-jaw or a good collet set are the way to do that for most things. Don't know about any other schools, but the one I'm in doesn't teach turning between center for accuracy. I've been reading the old literature, as I could lay hands on it, for much of the past 40 years, since I got out of my HS machine shop class and wasn't smart enough to take another class right away, and especially in the past dozen years or so since I got my first tiny Chinese lathe. I've been in that class, slowing (mostly two nights a week, when and as I can) and used the techniques I leaned on that tiny thing on the larger lathes at school, and they work there on their 8" 4-jaw chucks just as well as they did on the 7x10. Frankly, it's easier on the bigger lathes. More room for my XL hands. 

Bill in OKC

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On Sunday, March 14, 2021, 07:02:08 AM CDT, Jack Dinan <jack@...> wrote:

Eddie: This was very informative. 

I did resort to my 4 jaw for a job yesterday. 

In this particular case, I’m afraid the time to dial in the workpiece was a significant fraction of the work time. 

I’m looking into a 3 jaw that I can afford.

On Mar 12, 2021, at 4:50 AM, eddie.draper@... via <eddie.draper@...> wrote:

The problem with refurbishing the jaws on a badly worn 3 jaw is that they don't wear evenly. You can clamp a ring at the outer tips to load the slack in one direction and run a toolpost grinder in through the jaws, which sounds great and does indeed effect a major improvement so long as your lathe doesn't have so much wear that it turns tapered anyway, but it only perfects the system at that diameter. The jaw guides wear most where they are used most, so the taper on the jaws varies as you wind them in & out. The radius at each jaw improvement probably works, because the jaw screw and scroll wear should be even across all 3, though. The scroll radial register will wear, leading to slack in the concentricity.

It all depends upon what level of improvement you need. I have only one 3 jaw that I trust to be concentric and parallel and that is on my Myford ML7 at home. I bought the chuck new some years ago and I am the only user. If I want to be concentric on an old / well used lathe like the ones at the railway (I don't think the 1961 refurb by Sentinels on the 14.5" SB extended to the 3 jaw) the only answer is a 4 jaw and DTI, I'm afraid. On my usual sizes of jobs, the setup time is a relatively small proportion of the machining time, but for small stuff it gets frustrating. One thing you can do is to hold a 3 jaw in the 4 jaw and true it up to a ground bar in the 3, and that achieves repeatability across a succession of identical jobs so long as the jaw taper has been removed. Turning between centres is best when you have to keep taking it out to try on its mating part.


------ Original Message ------
From: "trackthatpot2000" <timmsken@...>
Sent: Friday, 12 Mar, 21 At 08:38
Subject: Re: [SouthBendLathe] recommendation for 3 jaw chuck

I fitted mine with a set of soft jaws, after a light skim with a boring bar using spacers to hold the jaws apart I ended up with the most accurate 3 jaw chuck I’ve ever had.

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