I was asked about my turning process. Specifically, about the limitations that I have when turning on a CNC (metal) lathe.
This is a diagram of my setup, it will look pretty familiar if you’ve ever used a metal lathe.
this is a picture of the exact same setup in real use so perhaps it will be a little easier to understand.
The toolholder runs on a track that moves on two different axises. “Z” moves left and right, “X” moves forward and back. Between these two, you have the coordinates for every move you can possibly make on a lathe.
You cannot use a tool outside of the toolholder – for example, a hand-held chisel. It would be extremely dangerous. There’s no rest for your hands and the toolholder won’t work as a rest because it is at a dramatically different height and you can’t change it (or the angle). It’s very rigid.
You take the tool and mount it in the holder, with grub screws. Your tool has a cutting end that resembles a scraper, and the rest of it is a rectangular block.
Now, I hope you can see where some of the limitations come in.
Something I want to make clear: I’m not complaining about how this works, but each method has its advantages and disadvantages, and this particular instance is a distinct disadvantage.
The absolute maximum diametre you can have of something in the chuck (however you mount it) is a tiny bit over 7 inches. Let’s just call it seven. (I think it is 7.12”. Might be 6.88”—I remember it is about .12” off but not which way…) At seven inches, your cylinder (let’s assume you threw a perfectly round cylinder in the lathe) is touching the toolholder when it turns and you may have a tool length of zero.
So now let’s put a cylinder in the lathe that is six inches in diametre.
You may now have a tool length of one inch poking out.
This is an example of what you can do with that much tool. On the back, you are fairly limited to depth (one inch) because the toolholder will hit the wood. If you have nothing that will collide, you can go in deeper. As long as at no point the geometry of the tool collides on either side (or into the live centre) you can get into some pretty big detail.
I’m sure at this point you are wondering why I don’t just cut the back and flip it like most of you do.
Because I cannot cut a stub into it and stick that into the chuck—chuck is too big, too forceful. It just throws them out. You either turn on centres, or on a flange/faceplate.
Trying to keep everything on centre this way is a monumental pain. I have done it before, but it’s rarely worth the effort.
And now, how you turn the interior of the bowl.
The same deal applies. As long as your wood won’t wobble (or won’t wobble enough to matter) you can dig in as deep as you can clamp a tool. In this piece the tool is comically short, usually I have 3-4 inches. I just ordered some tools that are six inches long.. look forward to doing some stuff with them.
It does go without saying that you can’t do things like hollow forming on this lathe. It’s fully enclosed.
Any questions? :)