Picking a Chuck for Your Metal Lathe
The Voice: Hey, Kevin. Where are you doing?
Kevin Caron: I've been playing around with the metal lathe. I have here a prototype for a wine goblet that a customer in Texas wants me to make, and I've been turning it out of a solid aluminum billet.
This (the wine goblet itself) was actually a part up here, and I just cut it off and started turning it down a little bit, trying to work on my shape.
I've been using this rough sketch on a piece of notepad and some basic measurements. The client sent me a few pictures over the phone. Right now I'm working on the shape.
As it turns out, I got my order of operation wrong - I got this section all round, then went to the mill and hollowed out the inside. I didn't think about what I was doing and made this hole in the top the same size as the outside edge. Now I don't have enough metal left inside to bring the top of my wine goblet a little closer, like a regular wine glass. I should have worked on the outside shape first, and left hollowing out the inside for later.
So, I'm going to take off my three-jaw chuck and put on the four-jaw, because this billet is bigger than this three-jaw chuck will handle. Now I moved the tailstock - that's this little piece on the end. This part is called a live center, because it turns, as opposed to a static center.
When I had the goblet in the three-jaw chuck, on this end, I had the live center over here on this end, to help keep everything straight, square and true as I was working and turning on it.
This part just helps support the other end of the work, so it doesn't slip out, or move around. I've got to move that part out of the way; then I can move the carriage out of the way.
This is the part that does all of the work. (This is an old Sheldon lathe from the mid-'40s, so it's built to last.) Just like that. It just turns off, and that's what it looks like.
Let me get the other chuck. As you can see, this one is much bigger and heavier, but it works the same. The smaller goblet would have fit in that larger chuck, but there's a reason most guys like to use the three-jaw chuck: You can put the adjusting wrench in any of the three different holes and as you turn it, you see the jaws all move at the same time, so it's self-centering.
With the four-jaw chuck - with the four opposing jaws on it - you can see when you try to adjust it that each one moves independently of one another. So, not only can you put an odd-shaped object in here - like a piece of square stock that you can clamp and then turn into something round, you can also put in a piece that's oversized. This one is a lot harder to use because when you put in a piece of oversized stock, it does not necessarily mean it's centered.
Now I have to get a dial indicator, come back off the carriage with a dial indicator, run it against this metal then slowly turn this around. Next I have to shimmy each of these jaws one way or the other - up and down, back and forth - until I get all the run out of it, so that when I turn it, this piece is centered and won't wobble. Otherwise I would have to start over, turn all that down to get rid of the wobble, but I'll still have a wobble in the part that's in here. Boy, there's a lot to learn.
Using my dial indicator I'll straighten this guy up. Then I can go back to work at making a new goblet, get my length where I want it, cut it off, get that (see, I did it again). I need to get my dial indicator, put it on here and get this true.
Once I'm done there, then I'll start my new goblet. I can turn this down to the right diameter and start to work my shape. I need to get my hole in the end so I can bring my live center over to support the other end of this.
There's a lot to learn, but it's fun. I'll see you next time.
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