I've seen matching sets of turned bowls that fit inside each other almost like Russian dolls. I've also heard turners actually say the bowls were cut out from the same piece so they didn't waste a beautiful piece of wood to make just one bowl. How do you do this on a lathe, and is there a name for the technique? Do you need special tools or is there a way to do it with a normal set of lathe chisels?
They are bowl coring systems like this
I bought this one and it has 4 different knife sets available for different sized bowls.
They are pretty expensive and each knife set is bought separately. I like it but you need some practice and they really aren't for the beginner, you need to have practice attaching the blanks to the lathe securely because there is a lot of force being used and I've had a blank jump right off the lathe. There are branches and other misc things inside a large hunk of wood that can cause the bowl to catch and that can be a problem.
I seem to remember a tool available at Rockler and that like, that was called a 'hollowing system'. It included a tool rest with a post, and a series of curved bar type tools (image a parting tool that has a long, large arc).
The point of this tool was that the curve of the tool and the setup of the post on the tool rest made a bit of a pivot. This allowed you to effectively cut and 'part out' multiple bowls from a single slug.
Sadly, I was not able to find this exact product online. It does exist, and with a curved hollowing tool, I'm sure you could achieve a similar function.
However, a word of warning: Making a curved 'slit' into a spinning lump of wood may provide ample opportunity for your tool to grab and bind in the space. Please be careful.
I Found it! Check it out HERE at Woodcraft*
*Not an endorsement of woodcraft, just the only place I identified it.
Yes, there are special tools. Basically it's a thin gouge on a curved shaft, plus guides so you're advancing it along the circumference of a circle. Bowl blanks are then undercut and separated working from the smallest outward, readjusting the guide between each division.
This does assume all the nested blanks will start out with the same inner and outer curvature, or that you get multiple curved gouges with different radii and appropriate guides for them.
It's presumably possible to do something similar without that tool, but it'd be more work and (probably) more wood wasted between bowls.