Faust M. Ruggiero
06-13-2011, 10:31 AM
I use my vacuum chucks most often as jam chucks. I like the security of having the tail stock in place. Of course, I turn on the pump to finish the very center of the bottom. As I've become more familiar with the system I use it more for applications. This weekend I worked with a friend who has been turning bowls for 10 years or more and he really uses his to the extreme. He cores most rough outs and uses a four jaw to hold the major blank. He cores from small to large so he only makes a tenon on the largest blank. After the rough outs cure, he mounts the convex side against a vacuum chuck and uses a taper extension to reach the inside bottom of the bowl to hold it against the vacuum chuck. He trues the area on the inside of the bowl that will contact his vacuum chuck. I asked why he trues this small and difficult to reach area. He has found a dried rough out will only contact a jam chuck on two opposing sides due to the nature of how wood dries. This creates a wedge that can theoretically split the bowl if too much pressure is applied via the tail stock. Truing the inside assures full contact with the jam chuck. With this area trued he flips the bowl around final turns and sands the outside, using the tail stock to hold the bowl against the vacuum chuck. The pump is not running for any of this.
He then turns the bowl around, uses vacuum only to hold the bowl (making sure he has sufficient vacuum) and final turns the inside of the bowl. When asked if he trusts the vacuum to hold the bowl in the event of a catch, he told me he trusts it better than any four jaw chuck. He has the vacuum gauge positioned so he can easily see it as he turns the inside. Certain woods can leak vacuum through the grain as they become thin but he uses other methods when using wormy or ring porous stock.
I tried his method this weekend and the bowl held well. I chose a small 10" rough out of pecan and mounted it on a 6" vacuum chuck. I'm not sure I am ready to give up the conventional method yet but I surely did gain more confidence in the power of the vacuum.
faust
He then turns the bowl around, uses vacuum only to hold the bowl (making sure he has sufficient vacuum) and final turns the inside of the bowl. When asked if he trusts the vacuum to hold the bowl in the event of a catch, he told me he trusts it better than any four jaw chuck. He has the vacuum gauge positioned so he can easily see it as he turns the inside. Certain woods can leak vacuum through the grain as they become thin but he uses other methods when using wormy or ring porous stock.
I tried his method this weekend and the bowl held well. I chose a small 10" rough out of pecan and mounted it on a 6" vacuum chuck. I'm not sure I am ready to give up the conventional method yet but I surely did gain more confidence in the power of the vacuum.
faust