In order to centre up the turning I switched the lathe on at low speed and touched a pencil point to the drive end cone. I then stopped the lathe and tapped on the side of glue-up where the pencil mark was and then re-started the lathe and touched the pencil to the cone again. After a few repetitions the pencil was marking the cone all the way around indicating that the workpiece was turning on centre.
Photo 13: Centring up
After one final tightening of all adjustments I used a roughing gouge to bring the octagon down to a cylinder.
Photo 14: Roughed round
I will be using a 2” forstner bit to rough out the inside diameter and I want the side walls to about ½” or so thick. There will be some loss in wall thickness when the box is re-turned after being cut in half, so I want to start with an outer diameter of about 3 ¼”. I use callipers and my parting tool to establish this diameter in a few spots along the length of the cylinder. I also part in to establish the tenons on the ends that will fit into the end caps. The tenons are made about 3/8” long and 2 ½” in diameter
Photo 15: Depth cuts and tenons
Then it is back to the roughing gouge to bring the cylinder down to size.
Photo 16: Cylinder sized
At this point I remove the piece from the lathe and re-mount it by gripping the tenon in the jaws of my four jaw chuck, using the cone centre on the tail stock to maintain its alignment while the chuck jaws are tightened. I check to be sure it is running true and adjust if necessary. Then I back off the tail stock and replace the cone centre with a 2” forstner bit mounted in a Jacobs chuck. With the lathe slowed down to 500 rpm or less I bore in a bit more than half the length of the cylinder.
Photo 17: Boring out the inside
Now I switch back to the cone centre and use it as an alignment aid to re-mount the cylinder swung end for end in order to bore out the rest of the interior. That completes the initial turning for the box body.
Photo 18: Tube turning complete