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.
Try It with a Sphere
John turns a number of spheres of various sizes. Previous to acquiring a vacuum chucking system, he hand sanded the ends where they were last attached to the lathe. With the task of hand sanding eliminated, the time it takes John to make and finish a sphere is dramatically reduced. Simply turn a sphere between centers (or by using a variety of other methods). Remove it from the lathe and attach it to a vacuum cylinder. Centering a sphere is a cinch. Because it’s already basically round, it self-centers. You can now make finishing cuts and sand the entire ball.
Touching Up Your Bowl
John travels to a number of craft fairs throughout the summer season, and invariably a finished bowl or plate will get scratched. Touchup is easy with the bowl attached to the vacuum chuck. Select a cylinder that’s appropriate to the size of the object, then turn on the system so that it will hold the bowl but not hold it too tightly. Move the object around slightly to get it centered. You might have to turn on your lathe to a slow speed to accomplish this.
Once the object is centered, you can lightly sand the surface to repair the damage. Blend the sanded area with the finished area. Reapply finish, either on or off the lathe.
Vacuum Chuck Cylinders
Cylinders in a variety of sizes for your vacuum system can be made from PVC pipe and O-rings, foam, chamois, or a used mousepad. Attach the PVC pipe to a backing board which can be made from any type of lumber, even MDF. If you use foam, don’t use a porous foam, as that will make the chucks too spongy, and they won’t hold.
John keeps his cylinder stored with the neoprene side down to avoid the neoprene separating from the cylinder. This neoprene will have to be occasionally replaced, as it doesn’t hold up forever with continued use.
John has an internal filter in his pump, helpful for keeping dust out of the system. Most homemade systems have inline filter systems. If you are creating a lot of sawdust, you might find it to be a good idea to install an in-line filter, even if you have an internal filter on your pump.
A vacuum chuck works by removing the air inside the bowl or vessel. Then the air pressure outside pushes the turned object onto the cylinder. Since air pressure varies in different parts of the world and with different weather conditions, the amount of pressure you’ll need will vary. In general, manufacturers call for about 20 to 25 PSI on the gauge, but you’ll most likely discover that the amount you need will vary within a greater range than that.
Having something fly off the lathe from a vacuum chuck is, for the most part, not particularly dangerous to the operator, but it certainly could cause the object to be damaged. A more worrisome problem would be a vessel imploding from too much air pressure. If that happens, the bowl could disintegrate with pieces flying everywhere. As with all woodturning operations, wear a faceshield!
Larger objects attached with a vacuum chuck are actually more safely held than small objects. This is somewhat counterintuitive, but it has to do with the amount of vacuum pressure required to hold small objects: the smaller the object, the more pressure it takes to hold the piece in place. If an object is small and thin, that’s a potential recipe for a cracked vessel or parts flying through the air.
If you are going to make your own vacuum system, be aware that you could end up with something that doesn’t work and in the end costs more than a commercial system. Do your research first on vacuum systems and the requirements for holding objects onto a lathe. With that said, however, I realize that many readers enjoy making and tinkering with new devices. If that’s the case, enjoy!