Opinions on chuck size

I understand your point about jaw extension in larger chucks, and part clearance over the cross slide. Up to now, my projects have been very short. The biggest was turning a pulley out of 6" diameter aluminum that was 2 1/2" wide, and my current chuck was at it's outer most limit. I won't be getting rid of my old chucks, but I do want to make sure I can get the biggest piece of metal possible chucked up in my machine. Ideally, I would just get a bigger machine, but I don't have the space and probably never will. An 8" may indeed be too big. It would be nice to try one before I went out and dropped real coin on it, but I don't know anyone locally who has one that I could test drive.

Thanks for the tip,

GG
 
Mister Ed said:
Terry, Did you ever get your new 6" chuck? What are your thoughts, if you did.
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Yes I did, just last week, in fact. Problem is I was too sick to do anything with it!

Keep in mind fellas that my budget is pretty limited right now, so I ended up buying Chinese instead of something really nice like a Bison or Gator. I had considered just waiting until I could afford to purchase a better chuck, but I NEED something better right now, as the original 5" that came with the lathe is not much good for anything other than a doorstop. I've gotten away with the old clunker for a while, but I find myself having to use the four jaw quite a bit, and I would like something with easier repeatability.

This chuck is a very old Buck, with a single pinion, and has had major repairs done to it where a jaw broke out at one time in the past. It is stiff in some places, and loose in others, the jaws are for the most part loose in their slots, etc. I could go on and on about what is wrong with it, but it would be a waste of time. I will let the photos tell their own story. The rust streaks you see are from a rusty pin that I cleaned up the last time I used the lathe, NOT from the chuck itself. I hate working with rusty material, but sometimes you don't have any choice.

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I purchased a Shars 6", three jaw, front mount chuck with reversible jaws. It's quality is better than I expected, and it fit my current budget. Since it is front mount, it can easily be moved to my 6" rotary table and get mounted to an adapter plate on it. Eventually, when I can afford a 6 jaw adjust-true chuck, the Shars chuck can become a more permanent accessory for the rotary table.

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This thing is massive compared to the 5" chuck, which seems odd when one considers that it is only 1" larger in diameter than the old one. I do like the fact that it has the oiler on the front, also. I did completely disassemble the new chuck to get the remaining grit out of it's innards (there was not much), and it is much smoother in operation now. I hope to get the backing plate machined today or tomorrow so that I can start to use the chuck. I will report back later on the chuck runout after I get it all mounted up.

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Keep me posted Terry. I am in the market, I think. I still have the original Logan chuck, but only the reverse jaws and it is driving me nuts. Like you, I probably cannot justify a new US made chuck.
 
The Shars chuck is also available in a rear mount version. Both versions list the total runout at .003", but the inspection card that came with mine indicates .0014 on this one, far better than I expected, and certainly within limits that I can live with. The rear mount version is a bit less expensive as well, about $10 less than the front mount if I remember right.

If you do work with tubing from time to time, a six jaw chuck may be more to your liking. There is a vendor on eBay that is offering a 6" six jaw with reversible jaws but is NOT an adjust true chuck. Here is the link: http://www.ebay.com/itm/160828698511?_trksid=p2055119.m1438.l2649&ssPageName=STRK:MEBIDX:IT I briefly thought about this one, but decided that a three jaw would be better for later use with my rotary table, thus I went that route.

I will post more as I get to working with the new chuck and get it set up.
 
GG,

Your 6" pulley would be fine on a 6" 3-jaw (or 4-jaw). The largest diameter that you can run on a 10" lathe if the chuck grabs it on the OD is around 8-3/4" because the reversible jaws will add about 5/8" on the radius or 1-1/4" on the diameter. Which is also on or maybe a little beyond the ragged edge of what you can run on an 8" chuck and still have enough teeth engaged to be safe. So to run an 8" dia. part you really do need an 8" chuck.

However, my 6" Pratt Bernerd SetRite chuck on a 1-1/2"-8 back plate weighs 27 pounds. According to the MSC catalog, the 8" equivalent weighs 46 pounds without the plate. You don't want to be swinging that around. So I would get a good or better quality 8" 4-jaw for the big stuff and something like my 6" 3-jaw for everything else.

Robert D.
 
One of the first things I noticed about my logan was the chuck. It's very short compared to other chucks. I think it's the stock chuck and a lot of Logan's I've seen have the same type. I think that's why you notice a large weight difference.
 
Ebel,

Yes. The original Atlas 3-jaw chucks are quite short, as well. I doubt that my original Atlas 6" 3-jaw weighs much over 10 pounds. The Pratt is over twice as long, and has heavier jaws. So, despite it having about twice the ID, it is over twice as heavy. The equivalent 8" is about the same length and has the same ID but weighs almost twice as much because the volume of a cylinder varies as the square of the radius.

The reason that independent 4-jaw chucks are usually shorter and lighter than the same diameter self-centering 3-jaw is that the 4-jaw doesn't have a scroll inside and aside from the grooves of the scroll, the 3-jaw is almost a solid cylinder except for the ID. Typically, the back of an independent 4-jaw is not solid or flat. In the back, a lot of metal is omitted in between the jaws. At least on threaded-mount ones.

Robert D.
 
Terry, If you've never used a chuck with 2 piece jaws, you're gonna love it.

Get yourself a set or two of steel soft jaws for it too. I use soft jaws so much, that I don't know what I'd do without them. They're easy to customize for shallow parts and they don't mark up finished parts for instances when you have to turn a part around on a finished diameter, ID or OD. A must have IMO.:))
 
xalky said:
Terry, If you've never used a chuck with 2 piece jaws, you're gonna love it.

Get yourself a set or two of steel soft jaws for it too. I use soft jaws so much, that I don't know what I'd do without them. They're easy to customize for shallow parts and they don't mark up finished parts for instances when you have to turn a part around on a finished diameter, ID or OD. A must have IMO.:))
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That is kind of what I was thinking, Marcel. My old chuck is missing the second set of jaws as so often happens with used equipment. There have been a number of times where I wished I had them, too. A set of soft jaws is definitely on the wanted list, and I have seen them in both steel and aluminum. In a worst case scenario, it probably would not be too difficult to make my own soft jaws.
 
For the benefit of anyone new to the art who doesn't yet know, the "second set of jaws" which are usually called the outside jaws, refers to the fact that on most self centering chucks, you cannot physically turn the complete jaws around in order to for example grip the OD of a workpiece whose diameter is over about 50% of the chuck diameter. This is because of the way that the truncated threads on the inside (hidden part) of the jaws are made. So almost all less expensive self centering chucks originally come with two sets of jaws. By the time that the chuck gets sold used, probably 80% of the time the other set has been lost. If considering buying a used chuck with solid or one-piece jaws, always make sure that it comes with both sets. Usually if it does, the seller will show them in one of the photos. If none show in any photo, it usually means that they are MIA.

The other type of chuck jaws, usually found on more expensive chucks, are called "two-piece". They have a set of master jaws that never come out of the chuck except for major cleaning. And a set of hardened reversible jaws attached usually by two socket head cap screws. The hardened reversible jaws can also be replaced with various types of soft jaws.

Robert D.
 
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