How strong does a vauccum pump need to be.

[Nathan Clark]

This is a two part question. As I can use the vacuum pump for stabilizing wood and for chucking. How strong does the vacuum need to be.
I came across two today on accident.

This first on I can likely pick up cheap. I can't find specific info on this model but I think its around 1.8 CFM and 25 HG
https://dl.dropboxusercontent.com/u/19832238/4qe.PNG
https://dl.dropboxusercontent.com/u/19832238/wet.PNG

https://dl.dropboxusercontent.com/u/19832238/sdf.bmp


This one is out of my price range, but I thought I throw it out there. I'd be surprised if it weren't enough I think it's built for sucking the condensed gasses out of AC units.

https://dl.dropboxusercontent.com/u/19832238/IMG_20140314_153352.jpg
https://dl.dropboxusercontent.com/u/19832238/IMG_20140314_153255.jpg

[Thom Sturgill]

There are two separate criteria here - CFM and level of HG. The system needs to have about 18+ in of HG to provide sufficient hold for safety. The holdfast generator advertises 20in Hg. The CFM determines how fast it gets there and how much leak can be tolerated while keeping sufficient HG. My system has a very low CFM but is VERY quiet. I have to seal porous woods before using it or it will not develop sufficient hold. Sorry, but I can not put a number to the CFM on my unit.

The other issue is will the design throw oil in the shop?

[John Thorson]

Right Thom, I never rely on the vacuum chuck alone unless pulling more than 20 HG. My unit pulls 3 CFM and it is fairly quiet but that is not enough CFM for porous woods. I would like go to 6 or even 10 CFM but that size pump seem to go up exponentially in price.

[Dick Mahany]

You mentioned wood stabilization. In order to pull the air out of a blank, you want the highest vacuum possible, but in this case CFM doesn't matter much. This is obviously different from the chucking considerations. Pumps that pull only 26-27 in Hg will be barely adequate for vacuum stabilizing, and the type of pump made for servicing AC systems are better as they pull around 29". Harbor Freight sell the AC service type pumps relatively inexpensively, although many folks have complained about the oil exhaust and have built filters to deal,with it. For me, I do both chucking and stabilizing and use a Gast 1/4 hp oil less vane pump. It is barely ok for stabilizing, pulls around 27" but has plenty of CFM for chucking.

[Nathan Clark]

You guys have been helpful thanks. Any other tips for a cheap vacuum pump?

[Scott Hackler]

Define "cheap". I bought a refurbished Gast rotary, oil less pump off an ebay seller for $159 shipped. I thought it was a good deal. It pulls around 26hg max.

[Greg McClurg]

Nathan,

Check out http://www.joewoodworker.com. You can get reasonably priced pumps through them and they work great.

Greg

[Phil St.Germain]

Nathan,

I have the same Gast pump as the one in the first picture and it does not look nearly as nice as the one you show. Over the weekend I finally got it set up for vacuum chucking. Works great. Pulls 18 to 20 on the beat up dial using a 4 inch PVC chuck. This was more than enough for bowls ranging in size from 6" to 15"

Phil

[Nathan Clark]

popped over to HF. This pump is cheap. I can't imagine it would last very long. But it seems to meet the minimum requirements. I'd buy it if it is sufficient for using a couple of times a year. Anyone have experience with it?

http://www.harborfreight.com/air-vacuum-pump-with-r134a-and-r12-connectors-96677.html#.UycXbfldW9E

[Dick Mahany]

That is what is known as a "vacuum generator". It works by a venturi principle and consumes LOTS of air to make vacuum. Your compressor may be barely able to keep up with it as it will need to run continuously. Especially hard for pancake compressors. I know they can be used, but have seen many negative comments comparing these devices as compared to a real vac pump.