Turning Archive 2006

Subject:
Vacuum Chucking Cylinder Seals

Bill Clark
>I just completed making a vacuum chucking system. I am using a Gast pump with a Holdfast Vacuum adapter through my lathe’s hollow spindle. I am pulling about 26 ½ hg at the end of the Holdfast hollow tube which is about the same at I got directly out of the pump. I’ve made three sizes of vacuum chucks out of MDF and PVC joint fittings. They have been sealed and the ends trued, and I rounded off the edge. The wall of the PVC is about 1/4”.

My problem is the seal at the end of the chuck. I purchased some 1/4” neoprene foam from Craft Supplies. The surface of both sides is rough and has no adhesive. For a test I cut a round from the neoprene big enough to over lap the cylinder walls and cut a large hole for the vacuum in the middle. When I attached two different bowls and tried to pull a vacuum I only got about 5 to 10 inches and the bowl was not secure enough to turn. The bowls were made of English walnut. One was 1/4” thick and the other 1/2” thick. I tried a flat piece of MDF with a 1/16” hole in the middle instead of a bowl and was able to pull about 20 inches of vacuum after I pressed the MDF really hard into the chuck cylinder. When the hole was plugged, I got about 23 inches. Next I tried some 3/8 wide by 1/4 thick vacuum tape (used for vacuum hold down jigs in the shop) on the rounded end of the cylinder. The results were about the same. I don’t believe the bowls were leaking that much air through the pores of the wood.

Is the contact area of the seals on the 1/4” rounded wall of the chuck cylinders just too small to obtain a good seal? I’ve seen many pictures of MDF / PVC vacuum chucks others are using and Craft Supplies even sells a kit to make them. What is the secret to getting a good seal? I would like to try some wider closed cell foam to wrap around the end of the cylinder. Can anyone give me a good source to order some? I have been unable to find any locally. Thanks to all for any help and suggestions.

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