Bowl bleeding on vacuum system

[Clay Fails]

I recently setup a vacuum system and my initial reaction is "wow, this could be a game changer". Far superior to the other methods I had used to reverse turn bowls (jam, cole, doughnut, etc).

I also discovered that all of the few bowls I've mounted this way bleed oil to the inside surface while being on the vacuum. Can any of you with more experience give me some tips to prevent this? My vacuum pulls about 25 inches with a good seal, with the bleeder valve fully open.

Ideas I have, but have not yet tried are:

1) Reduce the vacuum pressure. I don't know if this is a good idea or not, or if it would even help.
2) Let the bowl sit longer after finishing the outside before reverse mounting to remove and finish the foot


thanks!
Clay

[John Keeton]

Clay, this is hard to prevent, but it is actually air leaking through the piece that is driving the oil to the inside surface. Short of waiting, or adding a finish coat to the exterior to seal it better, you may want to try adding plastic wrap the the area that is finished turned to reduce the seepage. The foot/base area will still leak some air/oil, but I don't think you will be able to prevent the oil in that area from being pushed to the inside without waiting for it to cure.

[Dale Miner]

Clay, this is hard to prevent, but it is actually air leaking through the piece that is driving the oil to the inside surface. Short of waiting, or adding a finish coat to the exterior to seal it better, you may want to try adding plastic wrap the the area that is finished turned to reduce the seepage. The foot/base area will still leak some air/oil, but I don't think you will be able to prevent the oil in that area from being pushed to the inside without waiting for it to cure.

What John said.

And, 25 inches is way more than needed unless your chuck diameter is very small.

It sounds like you could do with a larger bleeder and if needed a chuck with a diameter that will positively hold your bowls with 10 inches of vacuum or less.

A 4.5 inch diameter chuck will hold a bowl for turning the foot with 10 inches or less. I do keep the live center against the bowl bottom until the very last bit.

For sanding the inside of the foot, it only takes 2 or 3 inches to hold the bowl in place.

[Jim Colombo]

Dwight;
I can't open your chart.

Jim

[Dwight Rutherford]

Here is a chart that shows the amount of suction exerted by inches of mercury and size of vaccum chuck.

[Dane Riley]

348574Here is one for smaller chucks.