Try It with a Sphere
Mounting spheres on the vacuum chuck is much easier because they are pretty much self-centering, and it offers a perfect space to sand all sides of the 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.
Various Considerations
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!
