vacuum chuck specs needed

[Karl Card]

I am looking at putting together a homemade vacuum chuck setup.

I have been looking at vacuum pumps and see some rated at cfm and some rated at Hg.

I have read some info saying that I need to get as near 25 Hg as I can.

How does Hg compare to cfm and what specs do I need to be in to have a descent vacuum chuck setup"

I have a chuck picked out and am bidding on it on ebay, it has the chuck, tube and rubber gaskets supposedly ready to hook the pump tube on.

I am not mechanically inclined but I figure I am going to have to start somewhere and get mechanically inclined...lol

[Rich Aldrich]

Karl,

I do not know much about vacuum chucks. However, HG is inches of mercury vacuum - a measure of pressure below atmospheric pressure. 30 inches is ideal vacuum which is absolute zero.

CFM is cubic feet per minute. This rating is the volume of air that is pumped. I would suspect that there should be a certain air volume in CFM that where the vacuum rating in inches of mercury can be maintained.

A pump has a performance curve where at different volumes of air pumped, there would be a coresponding vacuum that could be maintained.

The amount of area that you hold the bowl will increase the amount of force that is exerted at a given vacuum level.

[Karl Card]

That puts it in a better perspective...

http://www.berkut13.com/sucker.htm

this is what I am looking at trying to do ... any feedlback most definitely welcome.


I was floored when I googled vacuum pump and most of the returned headers were for penis enlargement pump... thats just not right..lol

[Thom Sturgill]

Chucks are easy to make but need either a dedicated faceplate or I thread the baseplate. All you need for that is some mdf (2 pieces 3/4" for backing) and a piece of pvc pipe (I used couplings) and something to seal with (I use the foam sheets WalMart sells in the craft area). Plans are available on the net, videos on YouTube.

As to the pump requirements, Hg and cfm are measuring two different aspects of the pump. I have a low cfm pump that will pull 25Hg - just not fast. Problem is it may not keep up with a leaky connection. That requires more cfm - One vendor sells 4.2cfm pumps and claims that much is needed. I have seen videos (Bob Hamilton comes to mind) of people using a vacuum cleaner (high cfm/low Hg) quite successfully with large area chucks.

The inches of mercury (Hg) will relate to the pull developed in psi. The size of the connection (area) times the psi will give the total gripping force, so I made three different sized chucks and always use the largest that I can.

Hope that helps, and good luck.

[Gary Conklin]

Great explanation Thom.

[Karl Card]

Thom,

You make it sound so easy.... I have no ideal why but I alwasy make things harder than they have to be... I alwasy have this thing that if it is to easy then it cant really work...

That was one of the most forward, to the point descriptions that I have seen in awhile about anything....

I am willing to bet that my vac and my face plate that sits on the bench will be active by tomorrow night... I will be wearing a helmet of some sorts...lol

Once again Thanks,

Karl

[Darryl Hansen]

Karl, try this site. Noble has some good schematics for setting up a vacuum system. He also sells used equipment and some he makes. Good source. Hg by the way is a measure of the strength of the the vacuum. CFM is a measure of the amount of air the pump will evacuate each minute. If your source is leaking higher cfm is needed. If you have a solid system any cfm will pull the vacuum but it takes longer to get to the max hg your pump is capable of pulling. http://www.wbnoble.com/

[Karl Card]

Just out of curiousity.....

how does a dust collector motor @ 2hp 220 volt with adapting it down to be able to hook it to a 3/8 inch tube..... due to a dc pulling dust and pieces then shooting them thru the bag or into the bag, would that suck the bottom of a bowl out or what???

not being stupid here just thinking, no I would not attempt it but at the same time wonder if it would or would not work...

[Tim Rinehart]

Just out of curiousity.....

how does a dust collector motor @ 2hp 220 volt with adapting it down to be able to hook it to a 3/8 inch tube..... due to a dc pulling dust and pieces then shooting them thru the bag or into the bag, would that suck the bottom of a bowl out or what???

not being stupid here just thinking, no I would not attempt it but at the same time wonder if it would or would not work...

I think the average 'decent' dust collector is good for about 10" water column pressure with the system closed off, no or little flow. That would equate to less than 1" Hg (mercury). The vacuum pumps are looking for closer to 20-25" Hg...so you would be seriously undersized on the 'pulling force', but by contrast, you could accommodate a HUGE leak.

I've heard people have used shop vacs, but you would be limited to using it for relatively large suction areas to get a decent area to pull.

Stick with getting a nice pump that pulls above 22" Hg and a couple CFM, I think mine is rated at 2.5 CFM. Less CFM, as has been said, will make it much more important to seal every little leak...and that can be difficult given the porosity of alot of open grained woods. I sometimes overcome that by just putting some masking tape over the exposed areas of the piece I'm vac chucking, to seal off leaks in the wood.