Vacuum chucking, how much cfm at the max?

How thin and what wood? Some woods leak more then others.

"Gerard" wrote: Looking around for a vacuum-pump I wonder how much cfm large, thin

^^^^^^^^^^^^^^^^^^^^^ Large thin-walled bowls require low vacuum, like maybe 5 to 8 inches Hg. The CFM of the pump is is not the question here. A high CFM pump will pull down more quickly, and tolerate more leakage, so you will have an easier time getting the bowl sealed and holding. A vacuum cleaner will probably do what you are asking, but will be limited whe you try to do small bowls.

Just want to buy an pump that will be sufficient for all circumstances as far as turning is concerned.

I understand this. But it seems comfortable to me to have a pump that covers all thinkable, practically speaking, circumstances. So what cfm will a large thin-walled bowl need?

"Gerard" wrote: I understand this. But it seems comfortable to me to have a pump that

^^^^^^^^^^^^^^^^^^^^^ I'm not sure you do, because you're asking the same question again. You want a pump that will cover all circumstances? You need a pump that pulls a good vacuum for the small stuff, say 18 to 26" Hg. And one that pulls a pretty good volume, so you don't have to fuss over leaks--say 2--3 CFM. My

3/4 HP Gast does just fine.

It's not possible to specify the CFM requirement to do a large thin-walled bowl. It's like asking what wheel base do I need to back into a parking space? ;-)

Been there, done that... I'd suggest Bill Noble..

He set me up with a used pump and everything else that I couldn't build, and he's VERY knowledgeable and helpful.. His stuff was reasonably priced and his help in answering all my stupid questions here and by email were "priceless"......

Just a note, the vacuum is minor compared to the surface area of the chuck you're using...

7 or 8 pounds with a small diameter chuck is VERY different than the same vacuum with a 4" or 6" diameter...

I've held 14" bowls on the lathe with the Vac cranked WAY down, because the holding power of a 4" opening is tremendous...

If ya have any specific questions of want links to "build your own", let me know, glad to help..

mac

Please remove splinters before emailing

Sorry, a little struggle with the English language, not my native language, you see. In the mean time you gave me some idea of a "pretty good volume". I can get a pump that will pull 5.8 CFM, so that will be sufficient. like the 2 car space to back in a mini ;-)

Gerard - before you make yourself really unhapy, please read my article on vacuum chucking, or at least skim the powerpoint overview - it's on my web page, wbnoble.com - click on vacuum pumps - or if you would rather go elsewhere, it's on my club's web page,

- click on tips -

I personally use a 5 cfm 3/4 hp gast vane pump - the leakage through the wood is not that much, but leakage through holes and inclusions is significant. Also remember, the larger the bowl (and chuck) the less vacuum you need - if you have a 12 inch vac chuck, a shop vac (that typically produces about 4 psi diference) will give you around 500 pounds of holding force - and a flow rate that is limited by turbulent flow in your fittings, not by the pump.

Short answer- yes, 5.8 cfm will be adequate

Found the PDF about Vacuum chucking on Bill's site: WOW! now there's something to read.

Already read something about imploding bowls and I understand the principles. I'll give a call when unexpected questions come up. ;-)

Thanks, 5 CFM is what the pump I had in mind will easily cover. I understand a lot of mechanic's like air-flow etc. Usually I fill holes and harden inclusions with epoxy, before finish-turning. Like I mentioned in the re of your short answer: I'm reading the PDF at the moment. Thanks for such a thorough article!

You're in the Netherlands?

I started using vac chucks 4 or 5 years ago and wish I'd built one long before that... They solve problems that I didn't realize that I had!

mac

Please remove splinters before emailing

Yes, I am. Utrecht to be a little more precise. I didn't acspect anyone from this group would be interested in the exposition of part of my works, but in the event zomeone is, you can find the info here:

and my website is:

Since thinking about a vacuum system, I realize how often it would come in handy, like for natural-edge bowls, a cylinder that fits into the bowl, or with longer conical object, which will fit into a cylinder, and of course the more common applications. Next to vacuumchucking, I'll use the pump for getting air out of epoxy, so cracks will be filled without voids.

I love the spalted beech. Resembles some spalted elm I had once.

Very nice work!

One of the many unanticipated uses I've found for vac chucking is putting things BACK on the lathe.. Going through some earlier work and seeing how crude it was, I put several pieces on the chuck and re-turned them thinner, refinished the crude ones, etc...

mac

Please remove splinters before emailing

Good tip! Tanks.