- A liquid filled vacuum gauge
- A needle valve to regulate the level of vacuum
- A small in-line gas filter to protect the pump from dust
- A cross fitting to connect everything
As the size of the bowls I've been turning has gotten larger the need for a vacuum chucking system has become greater. This is not so much for holding a bowl while doing the bulk of the turning but mostly for at the end when removing the tenon used to hold it in a chuck and cleaning up the bottom. The traditional way of doing this is with a jam chuck but those are a little fussy to get right and need to be sized for each bowl. Another popular method is to use something like cole jaws that can be customized to hold a bowl from the rim. These work but they are expensive and there is still a size limit. The method that I had been using was a bit of a cross between those methods. I have a set of flat jaws that I can screw pieces of wood to and then make something like a jam chuck but with the adjustability of a chuck. This worked really well since it could be set up to work with a few different sizes of bowls. The problem was that I reaching the limits of where I felt safe using it as I started turning larger sized bowls more often. The beauty of a vacuum chuck is that the larger you go the stronger it gets so it actually works better as the size of the bowls gets larger. The amount of force holding a bowl onto a vacuum chuck is related to the amount of vacuum developed and the area on which it acting so as the chucks (and therefore area) get larger the force holding the bowl on gets larger. Early this year I decided that it was time to do something about it. The first thing I needed was a source of vacuum and after a bit of research and looking around I settled on a used Gast rotary vane pump that I found on ebay. This is an oilless pump capable of pulling 4.5 cfm and reaches about 24 mm Hg while in use.