A bit of woodturning wizardry by Jerry Ritter.
A book Jerry recommends on turning spheres within spheres, or objects within spheres
Claude Lethiecq is a woodturner that inspired Jerry to take up this hobby after seeing examples of his work at an AAW Symposium in Minneapolis, Minnesota.
Examples of Jerry’s art, in this case these are lidded boxes turned within a hollow sphere (all turned from one block of wood).
Jerry explains each step in the process. The wood must be very dry and stable for this process.
Another example of a lidded box within a sphere. This sphere has 12 ‘primary holes’ and 20 ‘secondary holes’ turned in its surface as the outer sphere is hollowed and before the box and its list are turned.
Jerry mounts his hand-made (from PVC plumbing parts) ‘sphere holding’ chuck on a face plate. He has one of these chucks for each diameter of sphere he turns, 62mm, 80mm and 100mm.
The sphere itself must be absolutely round and for this level of accuracy a sphere turning jig is necessary. Jerry has a Vermec sphere turning jig, very accurate.
This jig has a ‘center locating pin’ to help with the accurate setup. If you look closely you can see the point sticking up from the center of the pivot. That point can be raised to meet ball to verify its position.
Checking the setup.
Although chucks can be purchased for this work Jerry likes the accuracy (and price) of his hand-made jigs.
Another view of Jerry’s ball holding chuck.
Once the ball in accurately turned into a sphere of the desired diameter the ‘design’ must be marked out on its surface. Jerry uses a compass and a bit of math to calculate the centers and diameters of all holes that must be drilled.
The holes drilled for a ‘sphere within a sphere within a sphere’ must be tapered, each inner sphere has a smaller diameter than the sphere ‘above’ it.
Jerry creates his own drill bits for this by grinding a common spade bit to the correct taper.
Once the holes have been drilled the ball is hollowed and the sphere(s) defined.
In the example in the image below we see that all 4 spheres are cut in each ‘primary’ hole in one positioning of the ball.
The 4 cutters used in this example for the 4 sphere ball. Starting from the bottom cutter in this picture it will cut the inside of the outermost sphere and the outer surface of the second sphere. The next cutter is removing the wood from the underside of the second sphere and cutting the outer surface of the 3rd sphere, etc. The 4th sphere is hollow in the middle.
The cutters in the photo above were purchased Jerry now creates his own cutters by silver soldering a bit of HSS to a mild steel shank.
You can see that HSS cutter on the tip of this holders in the photos below. The key aspect of Jerry’s design is that each cutter can be held securely and ‘swapped’ with another cutter in his set quickly because it is held in a common pocket in his holder. There is a set of these holders and cutters for each diameter ball Jerry turns, here we see the holders and cutters for a 80mm ball. Important – the radius of the pocket that holds the cutting bit equals the radius of the ball being turned so each cut uses the outer surface of the ball to accurately control the cut.
Those wooden cutting tool holders are used by holding them ‘flat’ on a special tool rest Jerry has created.
After each ‘primary’ hole has been drilled and ‘undercut’ with the special cutters all spheres must be held firmly as the next primary hole is worked on. Wooden plugs or ‘stiff foam’ plugs are used to hold everything together until the very end of this process.
So how do you sand and finish all of these inner and outer surfaces of all of these balls? Jerry has created special holder that used to keep various sections of the sphere from rotating as an inner surface is sanded, etc. There are times where strips of sandpaper are inserted in a given layer of the ‘multi sphere’ and an stream of compressed air is used to spin an inner sphere to sand it… Jerry did not demo that, ha!
By: Jerry Ritter On: 05/16/2024