"Going VAC....." - some specific hints and recommendations
Ruth:
I always recommend vacuum chucking as a very convenient and efficient method of work holding that minimizes potential secondary damage to variously sized and shaped turned pieces.
I usually begin my talk on vacuum chucking with the statement, "Once you go VAC, you'll never go back!" I rarely do jam-chucking any more, or use my "Cole" or "Jumbo" jaws on my scroll chucks for "rim-grabbing" when reverse chucking bowls to turn-off the tenon and finish the foot; and as others have already said, a vacuum system can be used for a wide range of other work holding possibilities.
A bit about the system itself: The Gast vacuum pumps that are rotary vane pumps are the type you should be checking for - stay away from membrane pumps, piston pumps, or oil-lubricated pumps if possible. The "23" series pumps are the ones that are used most often - the Model 0523, having an airflow rating of about 5 cubic feet per minute, would be a desirable flow rating and the 0523 is the pump most often sold by vendors like Craft Supplies and Packard that goes along with vacuum chucking systems they sell as a "package". Although some turners have successfully used pumps with lower air flow ratings, 5 cfm should work well for all but the most demanding applications. (e.g. Gast Models 0823 and 1023 have higher flow rates of 8 and 10 cfm, respectively). You may want to check that the pump with the system you are considering buying is in the '23' series, and is not a '22' series pump which has a MUCH lower flow rate. Depending on elevation, all of these pumps can generate vacuum in the range of 20 to 26 inches of mercury (in. Hg), but the flow rating gives an idea of the "strength" of the vacuum being pulled and more importantly, the vacuum being maintained in use. The manifold, vacuum gauge, and air leak valve in it allow you to adjust the level of vacuum your system develops. I usually have mine set at about 20 in. Hg when at stable vacuum in a closed system, which works well for all three sizes of chucks I have. There will inevitably be some leakage of air into the system between fittings and through the wood itself (see below), so don't expect a perfectly leak free system; it is not needed with a pump of adequate air flow rating.
I have used three Oneway vacuum chucks (3.5", 5.5" [most often], and 8") for several (many?) years, and they are quality items. Just be sure you have the appropriately-sized spindle adapters for your lathe. Making home-made vacuum chucks is also quite easy, and there are a number of sites on the Internet that show how to do this. I found that a small amount of silicone caulking around the adapters reduces air leakage (and more importantly dust contamination) into the system by creating "mini gaskets' where needed. Quite a simple solution if you do have leaks around the drums or with the spindle adapters.
You should use heavy walled rubber or other plastic tubing to connect the pump to the manifold and air leak (vacuum adjustment) valve, as well as between the manifold and the rotary vacuum adapter on your lathe. Using tubing with walls that are too thin can result in tube collapse and loss of vacuum holding. Similar to the recommendation by Bill, in my system I included an in-line particle filter between the lathe and the manifold to protect the manifold and (more importantly) the vacuum pump from wood dust and other particles that will infiltrate through your system if given the chance by being sucked into the system, or even through more porous woods. You want to minimize contamination getting into the pump which can shorten vane life.
One final recommendation I have that you should really heed is that you never want to apply liquid finishes to turned wooden pieces while it is being held in a vacuum chuck! The vacuum will literally pull the finish thorough the wood, creating a real mess inside the vacuum chuck, and potentially into the lathe spindle bore, etc. as well. Novice vacuum-chuckers do this only once, which is a real lesson in understanding the porosity of wood being held by a vacuum! Shellac, oil, lacquer, poly - it doesn't matter. Liquids WILL pass through wood being held under vacuum! Please learn from my experience, and don't even try this!
I hope these comments have helped you a bit to get a better feel for what you should be looking for in a vacuum chucking system. If you have additional specific questions about set-up or use, let us know!
Rob Wallace
