Thursday, February 9, 2017

Does Your Vacuum Chuck Leave Marks on Your Bowls?

I recently turned a Maple Bowl, when I mounted the bowl on the Vacuum Chuck and turned the bottom of the bowl, the vacuum chuck left a circular mark in the bottom of the bowl.  Needless to say I was very disappointed and started looking for a fix, below is a solution.

 This is the 6" Vacuum Chuck that I used on the Maple Bowl; the bowl is about 13 inches in diameter.  Notice the hard plastic between the two o-rings, that is what leaves the mark.  Larger Diameter o-rings might help the problem, but they will compress to seal  the vacuum chuck to the bowl and the hard center will be in contact with the bowl.

Enlarge the picture and you can see the mark left by the vacuum chuck, just above the blue tape

 This is Neoprene gasket material, it is about 1/16 inches thick. This material is fairly stiff but soft and flexible enough to seal
Neoprene gasket cut out of the sheet.
 Glue the gasket to the Vacuum Chuck.  I used contact cement in three or four locations on the hard center.  Avoid any large buildups of glue or debris under or on the gasket as this will not allow the gasket to seal.
 Gasket glued to the chuck and under vacuum.  Used a piece of heavy plastic so I would be able to see how the gasket reacted under vacuum.
 Vacuum gauge at 27 inches of vacuum.  This is the same amount of vacuum without the gasket.  I mounted a bowl on the vacuum chuck with the gasket and the chuck left no marks.

I think my gauge is off a little bit, it should read close to 30 inches of vacuum, because I am near sea level.
Here is the whole setup.  I purchased the parts from different suppliers and built the vacuum chucking system myself, saved a about $250.

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