Vacuum Chucking Question - Which Pump?

[Matt Owen]

I am wanting to build a vacuum system, and am a little confused on which pumps are okay to use.

It looks like rotary vane pumps work, and I have also seen diaphragm pumps used. Would a piston/rocking piston pump work just as well?

Also, does the horse power really mater? It seems to me that as long as you can pull a certain amount of vacuum, the horse power shouldn't really matter too much. Is there anything that I am missing with this?

Please let me know. Thanks,

Matt

 

[Mark Warden]

Anything that pulls 20 or more on your gage should be fine.HP does not matter within reason you don't want to use something so small it can't keep up with minor leaks and rotary is preferred because of heat buildup.Not that I would know because I have yet to build an adapter that doesn't leak through the bearings.:mad: bur if you do a search for vacuum or vacum for those of us that can't spell (me) here you will find a ton of info you'll only see a few posts but they have many good links in them.

 

[Rick H]

Mark
The first one I built I used 1 bearing, it pulled about 20. The next one I built I used 2 bearings on the same design and it pulled 26 using the same chuck. So I don't think bearings were made for a perfect seal, try using 2 the next time.

 

[Ed Heuslein]

Howdy Matt: I've built probably over a dozen vacuum systems over the past 10 years for myself and others. That said, your question may depend upon how you plan to use your system. I have two. One is mobile, attached to a two-wheel dolly, that I can use remotely, such as demonstrations. It uses a rotary-vane pump. My permanently installed system in my shop is a junk automobile A/C compressor (mine is a York), powered by a 1/2hp ac motor (an old wash machine motor works great). The pump I get as a "core" from a local auto A/C shop (I paid $20 for the last one a couple years ago). The thing you must watch for when getting these cores is that the "low" side, or vacuum side, works. Normally the "high" side of the compressors is what dies in them and you don't care about that. Also, that it turns freely (bearings are still good). Mine has been in service for about 7 years. I check the oil about every 6 months and occasionally must add just a little (maybe a half cup). It draws 24hg before being hooked up to my lathe. Then I loose a couple hg, but it's no problem. Compressors from smaller A/C units such as refrigerators, etc., do not have enough cfm to work very well so stay away from them. Lastly, when using your new system, make sure you turn off your lathe BEFORE turning off the vacuum pump. DAMHIKT.

 

[Don Meyer]

How many cfm does a vacuum pump have to produce for an effective system?

 

[John King]

Vacuum Chucking

Checkout Bruised Brothers, SWAT Demo, "Building a Vacuum Chuck," bottom of the right column at http://www.goldentrianglewoodturners.org/.

There's a lot of info there on vacuum pumps, adapters, vacuum requirements, etc. - John

 

[Bill Turpin]

Inverse square law

CFM of a vacuum system is inversely proportional to the square of the diameter or distance. English translation: if you double the hose distance, you get one-fourth the flow. If your smallest orifice area is half the size, you get one fourth the flow. A 1/4" hose will carry only 19.8% flow of a 3/8" hose or pipe. Examine internal diameters of your fittings . A single fitting with the smallest diameter always wins the fight. Brass fittings can be drilled out since pressure is not a concern. A used, empty 30# freon cylinder inserted between the pump and lathe will give a few seconds of reserve to save the bowl when the power suddenly goes off.

 

[Rick Meier]

Here's another link with tons of details on building your own vacuum system:
http://carlford.info/assets/demos_classes/vaccum_chucks_demo/Vacuum_Chucks_Demo.pdf

 

[Matt Owen]

Thanks for all of your help. With all of your information, I think I'm on the right track. Now I just have to do some shopping. Thanks again.

Matt

 

[John King]

Vacuum Check Valve

Check valves for vacuum service are available from McMaster-Carr. See http://www.mcmaster.com/#catalog/115/477/=3qy4hv. A check valve will preserve the vacuum on the bowl long enough for a safe shutdown of the lathe in the event of a power failure at the vacuum pump. May want to consider this if an empty freon cylinder is not available. - John

 

[Dick Hines]

Check out Supplus Center. They had a lot of pumps a while back. I built a system last spring for about $150. That's pump, fittings,tubing,and filters.

Love it! Don't know how why I waited so long to build one.