vacuum chuck ?

[Bill Bolen]

My shop vac powered vac chuck system works quite well on larger deep bowls but just does not have the required pressure for NE's, boxes or smaller very shallow pieces. My question is what is the minimum cfm you vac users would recommend? Thanks...Bill..

[Bill Bolen]

Anyone able to answer?

[Ted Evans]

Hello Bill, I do not have a lot of experience at turning but the Holdfast system that I have has been quite satisfactory holding some small NE walnut bowls. It runs about 22-24 inches of vacuum. I use the 3 inch chuck. I am also interested in what others experiences are.

Ted

[John Frigillana]

I just finished my vacuum chuck and have used it. On a NE bowl, I have a 3"bell that I used to chuck it too. My Vacuum pump puts out 6CFM. The HG has to be turned down to under 20, depending on thickness of NE bowl. I also use the tailstock till there is just a nub left. Just to be safe.

[Sid Matheny]

I also use a shop vac with my Nova DVR-XP and have been happy with it but I don't turn many NE's. Sorry I'm not much help.

Sid

[Steve Kubien]

How does one use their shop vac for a vaccum chuck?

[Sid Matheny]

Steve, Bob Hamilton's video is a good place to learn about using a shop vac.

http://www.youtube.com/view_play_list?p=FCFCB8CA2B04E33B

Sid

[Richard Madison]

Bill, your question is sort of "apples and oranges". What you probably need is not more flowrate, but the ability to pull a slightly harder vacuum. While the shop vac will probably pull only a few inches Hg of vacuum, with a large piece that still creates considerable clamping force on the work. A small piece will require a considerably harder (more inches of Hg vacuum) vacuum to create about the same clamping force. The best example of this is the vacuum cleaner ad that shows the vac lifting a bowling ball. Note that the "chuck" is almost as large as the ball. If the chuck was only 3" in diameter it would not lift the ball. Hope that made sense to you.

[Gordon Seto]

http://www.woodturners.org/tech_tips/vacuum_chuck/vacuum-chucks.pdf
(Pages 4 & 5) explains what you want to know. If your system is not leaking (poor seal, thin wall, porous wood), probably you don't need a high CFM. The holding force is more related to the diameter of the chuck.

[Don Geiger]

Just a note of caution: Shop vacs rely on flow through the motor for cooling. Rotary vane vacuum pumps do not.

[Joshua Dinerstein]

My shop vac powered vac chuck system works quite well on larger deep bowls but just does not have the required pressure for NE's, boxes or smaller very shallow pieces. My question is what is the minimum cfm you vac users would recommend? Thanks...Bill..
Bill, I bought the middle Vacuum pump at HF. Which is I think a 2.5 cfm pump. It will draw an almost perfect vacuum. I haven't tried many small shapes with it yet but it draws pretty darn strongly. I got it for $69 on a pretty good sale at the local store. I can try to test some smaller pieces this weekend and see how well it works for me. But all in all right now I am extremely impressed with how well it works.

Joshua

[Steve Schlumpf]

I agree with Richard - it is not the CFM you have to be concerned with - it is the size of the chuck and the amount of hg you have that determine if the system will work or not.

The CFM makes a difference if you are turning wood that is porous, has small holes or otherwise leaks small amounts of air into the system. In that case you have to be able to remove the air faster than it is coming in - in the process, creating a vacuum.

There are formulas that show how much pressure is applied to a turning and they all depend on the hg applied and the size of the chuck. Basically, at any given hg, if you double the size of the chuck, you quadruple the force that is applied to the turning. So, the opposite is also true. If you go from a 4" chuck to a 2" chuck and your vac system applies the same hg - you just cut your holding pressure to a quarter of what it was.

When you have to use a small chuck to hold your work, the only option that I am aware of, is to increase the amount of hg applied.

Hope that helps somewhat. If not ... ask.

[Bill Bolen]

Thanks for all the info folks. Makes much more sence to me now. Now to open that tight fist of mine and get the vacuum pump...Bill..