For a lathe, what CFM rating should a vacuum pump have?
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Vacuum pump CFM
- Thread starter Webb Willmott
- Start date
If your system is near-leak-free (which it should be) and your bowl doesn’t leak, then flow rate isn’t very important. What is important is the ability of the pump draw a strong vacuum - I like to see at least 25 inches of mercury, often work at 27 inches.
Tim
Tim
3-4 cfm should suffice. I use a 1/4 hp Gast rotary vane pump for chucking and pressing veneer, which has worked well for me at levels >20 in. hg An absolute vacuum at sea level runs just under 30in. hg (depending on the weather). You might want more volume with thin vessels or porous woods. The actual clamping force is a product of area and vacuum level. With a small diameter chuck a higher vacuum level is more important. With a large bowl on a flat vacuum chuck a high vacuum level can actually implode the piece so you may want a pressure gauge and valve in the system to modulate the clamping force. I once imploded a curved lamination form with inadequate internal bracing and it got my immediate attention.
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At my club in Erie PA one of the members lived next door to the owner of an appliance store and when he took in refrigerators or dehumidifiers he kept the pumps. He then gave them to our member as needed. I would then build a vacuum system with a pump and sell them to club members who would then pay the club $30 something. I have been using the first one I built for 16 or 17 years now and it still pulls 26 or 27 in. Hg. I had purchased before hand Gast 220 volt pumps but have never needed to use them as the little dehumidifier 110 volt pump works. I have a different system with a store bought pump for my CNC machine (also 110 volt). I have successfully finished pieces that have pulled just 16 in. Hg. I do feel a lot safer when the vacuum being pulled is 25 in. Hg or greater.
Two things you need, CFM to overcome leaks, and a good enough pump to reach a low vacuum level. Most woodturners will be more than happy with a pump in the 3-4 CFM range, and you'll want to be be able to get at least in the 20 in. Hg range, if not more. Actual vacuum you can get will vary on the ambient air pressure, also effected by elevation. If you're in a Denver, you'll pull less vacuum than in San Diego. Another thing people ignore is the size of the chuck. Larger chucks have larger surface area, and that's more area for the vacuum to work with.