Lathe chucks, what do I need, and what size?

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grhm

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When I bought my lathe, it came with two chucks; a 3-jaw 6" and a 3-jaw 8". The 6" is currently mounted on the (Enco 12x36) lathe, and I do not know if the 8" has the proper backing plate (it has one, unthreaded, that I have not measured). Since I have two chucks and both are 3-jaw, I figured I might want to arrange such that I have a more useful selection.

I have three questions, then:

First, should I not worry about a 4-jaw and just stick with the 3-jaw? I would have assumed that if one only had a single chuck, it should be a 4-jaw, but it's entirely possible that I'm incorrect in this assumption.

Second, is it useful to have both a 6-inch and 8-inch chuck for this lathe? If not, and I'm only going to keep one, which size is a better fit? If I acquire a 4-jaw, what size should I choose?

Last, is there any way to know or even guess at what backplate I'd need?

Thanks for all your help and advice!
 
Chucks are another type of tooling, and it's hard to have too many tools ;)

1) You'll definitely want an independent 4-jaw at some point. You can dial in some things to closer zero on a 4-jaw that you can't do on a typical 3-jaw. This becomes important when you have to remove and re-insert a part, perhaps to flip it, or if you are working on an existing part that you want to center up for further work. It's also hard to hold a square part in a 3-jaw, and you can even turn things off-center in a 4-jaw.

2) Smaller chucks tend to have a smaller minimum diameter that they can clamp on to, so there is justification for having a bigger chuck for larger items and a smaller chuck for smaller items. The differences between a 6" and 8" isn't that great though. Larger chucks tend to have a lower maximum RPM too.

I don't have any ideas on what backplate an Enco uses.
 
If they're both self centering scroll chucks and you only want to keep one, bigger is usually the better way to go. Accuracy is another factor to consider, a good small(er) 3 jaw can be handy also.
Definitely "pull your finger out" go get independent 4 jaw, you'll need it soon enough.
What size? The biggest that will fit, jaws fully extended but not contacting the carriage(on the "chuck" side of it, not over the cross slide).
The 3 jaw you may want to clear over the cross slide.
 
My 1440 lathe came with a 6" scroll and an independent 8", 4 jaw. The lathe has a D1-4 spindle and the chucks that came with it had that as an integral part of the chuck. Both have served me well. I added a set-true type of 5C collet chuck that I use for smaller things, 1 1/8" max collet size. I added an 8" 3 jaw scroll chuck that is face mount so I can also use it on the rotary table. I had to buy a D1-4 blank back plate and turn it to fit the chuck. The chuck has reversible jaws and is a high quality with very little runout. It is heavy, so I made a wooden block that it fits on and the block fits the bed so I can slide the chuck right onto the spindle. My lathe also came with a 12" back plate so I can bolt odd shape parts on. Rarely used. Turning between centers is the best way to be able to reverse the work. It requires a dead center that fits the spindle or adaptor, a (live) center for the tail stock and a means of driving the work, usually a lathe dog. Watch some Joe Pie or Blondihack videos for methods. Blondihack has a series of good getting started videos.

No idea what spindle mount your Enco has. Take the chuck off and measure and compare to online info. Or put a photo of it on this site with measurements. I'm sure someone here can help identify it.
 
You will want a 4-jaw at some point, and the 8" 3-jaw you have is probably of limited use (can't open jaws very far without hitting the bed)
-Mark
 
Personally, I'd keep both chucks. There other uses for chucks such as mounting them on rotary tables. If you have to keep one, select the one with the best condition and precision.
 
Every lathe needs at least 3 spindle mounted holding devices.
a) 3-jaw scroll chuck: for speed and ease of use
b) 4-jaw independent chuck, when you need to get a part concentric
c) face plate to mount those odd parts for boring.
 
I don't think any of the chucks are of any special value. Speaking of value, where to get a good-value 4-jaw independent?
 
Chucks You need lots of them. I have two 8" 4 jaws. One is set up normal and the other has the jaws reversed. Wish I had an 8" 3 jaw. I have a 6" 4 jaw. I have a 6" and a 5" 3 jaw. One is set up normal and the other has the jaws reversed. I have a 3" 3 jaw. I have an ER32 collet chuck and 3C collets. I have a drill chuck for the spindle. And an 8" face place. Then there is the spider on the outboard end of the spindle. I have not used the 3C collets. I rarely use the 3" 3 jaw and the drill chuck. The rest of the chucks get used all the time depending on what I am doing.

Never sell tooling. You will regret it sooner or later. Bare minimum is a 3 jaw, a 4 jaw, collet chuck, a face plate and a spider. Buy the best quality you can afford. You can make an ER collet chuck and the spider.
 
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