Of the many ways to attach something to a lathe, vacuum chucking stands out as particularly useful for objects that seem to defy any other method of attachment. Two such types are 1) bowls that have already been finished but need a bit of touchup and 2) spheres. I don’t own a vacuum chuck, so I did the next best thing: I visited John Lannom in Cincinnati. He owns a vacuum chucking system, and he uses it regularly. He showed me several applications of his system, carefully explaining the finer points and drawbacks of each step.
John’s vacuum chuck is a commercially purchased system, made by Oneway Manufacturing. There are others. Many turners have also put together their own vacuum chucking system, and you certainly could, too, given a bit of research (look up “vacuum chucking for woodturning”). Either a commercial or a homemade system works well, and both alternatives have their good points.
Vacuum chucking systems have their limitations. John pointed out that very thin-walled vessels can be crushed, even with a small amount of air pressure from a vacuum chuck. Also, a vacuum system does not hold as securely as do scroll chucks and faceplates. Additionally, turned items with holes in them (such as those made from wormy ash) are not good candidates for vacuum chucking: the holes simply let the air flow through rather than creating a vacuum.
Basic Concept of Vacuum Chucks
Vacuum chucks basically hold an object to a lathe so that it can be lightly turned or sanded without leaving any marks from being attached. Such a system provides total accessibility to sand and finish objects. The contact point between wood and cylinder is a soft seal, often made from neoprene. Use of this type of material lets you avoid any marks on your turned objects. Different size cylinders allow for attaching variously sized objects.
Commercial systems come with a vacuum pump, rotary adapter, air hose, vacuum gauge (or regulator) and vacuum cylinders. Each item can be purchased separately, or the complete package can be ordered with the cylinders threaded to fit your lathe’s spindle size.
Finishing the Bottom of a Shallow Bowl
After explaining his vacuum system, John showed me the steps involved to reattach a shallow bowl to the lathe in order to turn the bottom. The bowl was originally attached to the lathe using a scroll chuck grabbing a tenon (or foot) on the bowl’s bottom. John needed to clean up the inside of the tenon to create a finished base.
With the bowl turned and sanded and still attached to the chuck, John removed that assembly from the lathe. He selected the medium-size vacuum cylinder and threaded it onto his lathe’s headstock spindle. The vacuum system was already set up on the lathe, so the next step was to somehow reattach the bowl to the cylinder, getting it centered.
This is where things get a bit tricky: the object must be reattached to the lathe, keeping in mind that there are three axes, each of which could be out of alignment. It can be done, but it might take awhile. Or you can get lucky and hit it right on the first try.
A Solution to Centering
The folks at Oneway Manufacturing have figured out an ingenious solution to getting something centered back onto a lathe in a vacuum chuck: it’s an adapter that screws onto a chuck. This adapter allows the turner to keep the bowl or plate in the original scroll chuck, yet be able to reattach it to the tailstock spindle. Doing so ensures that the plate or bowl will be aligned with the lathe’s axes.
Since John’s bowl was already attached to a scroll chuck, he simply removed the chuck-and-bowl assembly from the lathe and affixed an adapter to the chuck. He then threaded the chuck onto the tailstock spindle. Presto … immediate centering!
From this point, he moved the tailstock down the bed of the lathe so that the inside of the bowl made contact with the vacuum cylinder. He opened the valve on the vacuum system, which attached the bowl on the headstock. It was centered!
John removed the chuck from the back of the plate, and the result was complete access to turn the bottom of the bowl.