Vacuum chuck/pump questions

[Scott Hackler]

So I sprung for a rebuilt Gast rotary vane vacuum pump and have been assembling all the needed things to do vacuum chucking. Tonight, even though it's not 100% assembled (still going to build a cabinet to hold it and build a muffler to quiet it down) I fired it up to see how it goes. Put a smaller walnut bowl on it and closed the bleed off valve. 27" hg. I thought that was pretty decent and I was able to take the tenon off and finish the bottom very nicely.

So after doing that and sanding the outside of the bowl and foot, the pump was hot to the touch. Is this a normal thing? I also noticed that my rotary union was a little warm too.

[Alan Trout]

Yes pumps will get pretty hot.

[Scott Hackler]

Thanks Alan. I guess I should have just texted you in the first place! Is 27" pretty decent?

[Faust M. Ruggiero]

Scott,
Try this experiment. Allow a bit of air bleed through the valve. Yes, your vacuum inches will drop a bit but 27" is tons of vacuum and a bit less vacuum will still hold the bowl. The bit of escaping air will cool the pump. My first vacuum pump, a brand new 1/4hp Gast, would often overheat and the internal safety would shut it off. Running it with the slightest bit of air bleed, just an inch or two, solved that issue. Depending on your wood specie, trying to vacuum chuck a thin bowl will require you to use all available vacuum and will still not register 26 or 27 inches because the bleed is coming through the end grain. You will have to figure out how little vacuum you feel safe with. Just be sure to use as large a chuck as you can.
faust

[Josh Bowman]

Yep, my gast gets hot. But I'll ask, how long can you keep your hand on it and where is it hot.

[Tim Rinehart]

Sounds like excellent vacuum Scott. The other thing about having a bleed valve that's handy is that given how thin you like to turn, you may not want full vacuum on a piece for fear of imploding it. I've never had it happen, but why risk it. I normally use my vacuum only for the parting/cleanup of the bottom of a piece, and I can get by just fine with a 3" chuck holding at 20".
I'll just throw out one other bit of advice. I use a threaded adapter, 2MT on one end and 1-1/4" threads on other to go into my chuck holding the piece I'm ready to reverse. With that piece now sitting in the tailstock, still in the chuck, I bring it up to the vac chuck and will wrap shrink wrap around the piece and chuck, then release it from the 4 jaw chuck. This gives me a bit extra hold when alot of vacuum leaks thru the piece, and it affords a little extra protection against coming loose. For really heavily voided pieces, I've done this without any vacuum at all and very light cuts and no problems.

[Dick Mahany]

I have a Gast rotary vane pump and it does indeed get hot and is noisy. Attempts to muffle it haven't been successful but with the temp, I didn't want to put it in an enclosure for fear of overheating. I use it for wood stabilizing with a vacuum chamber in addition to chucking. When stabilizing it can run for several hours, but I've never had a problem.

[Grant Wilkinson]

I, too, have an older Gast vane pump. Gast says to run them for a few minutes with no vacuum before you shut them down. I'm not saying that I do it every time, but it does seem to cool it down quite well. You can read the shut down procedures on the Gast site.

[Alan Trout]

Scott 27" is great. That would break a thin bowl. I usually adjust mine to about 22" to 23" just to keep from breaking anything.

[Steve Schlumpf]

Scott - 27" is more than you'll need to hold something! My Gast gets warm during use but nothing extreme. I let it run and suck in air after I am finished - usually for a couple of minutes before I shut it off.

The one vacuum chuck that I use the most is 3" but I also have one that is 4". I usually run with the gauge set at 20" and that is more than enough.

Just for fun - throw a bowl or something on your vacuum setup, turn the vacuum up to 20" and see if you can pull if off your lathe. You will be surprised at how difficult that is!!

Also, there are a number of charts out there that list what the actual pounds of pull are for the applied vacuum. I think I have one or two if you can't locate one.

[Dick Mahany]

Even 23-24" can be pretty amazing depending on the diameter of the work and the porosity of the material. I once finished a 7" spalted burl platter and could visibly see it flex inward at 23". To my surprise, when I released the vacuum, it had pulled the finishing oil clear through to the backside!

[Scott Hackler]

Thanks for the info. I am now rethinking my idea to build an enclosed wood cabinet to house the pump, with a drawer for accessories. It might get too warm/hot inside a cabinet.

Dick, I have an idea that I am working on for a DIY exhaust muffler. Once complete I will evaluate if it quiets things down and if so I will post the instructions and parts list.

[Bob Bergstrom]

I rarely close the bleeder valve on my Gast pump. Sometimes I have worm holes, but that's about it. It sits on a shelf and never seems that hot, just warm. I do blow the dust out regularly. Make sure you have a filter on the bleeder valve besides the line one. I clean those filters on a regular basis also. Enjoy the vacuum system. They are wonderful, and you will find more uses than just turning bottoms.

[Dick Mahany]

Thanks for the info. I am now rethinking my idea to build an enclosed wood cabinet to house the pump, with a drawer for accessories. It might get too warm/hot inside a cabinet.

Dick, I have an idea that I am working on for a DIY exhaust muffler. Once complete I will evaluate if it quiets things down and if so I will post the instructions and parts list.

Scott, I tried a short piece of pipe into an upside down spice jar packed with cotton for a muffler, but it didn't make much difference. I look forward to a solution if you develop one.

[Tony Shaftel]

To solve the noise problem I put my Gast pump in the next room (happens to be a shed I built off the back of the garage), connected by a ten or twelve foot run of 1/2" flexible plastic hose. Worked great for several years, then the vacuum level dropped off significantly. I put in a rebuild kit. No improvement. So I carefully checked the hose run...and found a rat had gnawed a hole in it. Replaced hose and de-rodented. :-)

I always run with the bleed valve open to some degree. I only use the vacuum chuck for finishing the foot of the bowl and then resanding/finishing up the side of the bowl if necessary after that. Instead of a chuck that you place the bowl over, I prefer to use a large flat mdf or plywood circle that can accommodate the whole top of the bowl. This of course places the whole bowl under vacuum, and I have seen them begin to visibly distort if the vacuum is too high. But I don't have to worry about the bowl coming loose should I press too hard on the side.

[Jeffrey J Smith]

Mine sits in a cabinet right next to the lathe - same rolling cabinet with drawers that my grinder sits on. The front is sealed, the back is open (with a little filter material over it). Has never gotten warm enough to trip the thermister - yet. As far as any noise - the cabinet muffles most and a sintered metal filter on the inlet seems to soften what's left.

[Jim Silva]

Hi Scott,
I've just put together a vacuum system (although I'm using a cheap HF pump) and can pull 25+ with it. I wanted to enclose mine to keep choking it with dust and to minimize the slight oil mist that can come from the pump I'm using. I figured that putting it into a cabinet would be a heat issue so I built a little wood frame around it and covered the sides and top of the frame with that blue fiberglass furnace filter you can buy at Lowes/Depot. Comes in a 30x20 sheet and two surrounded the pump nicely.

It's designed to filter air so heat buildup shouldn't be an issue and it also serves as a slight barried to the oil mist issue.

Don't know if that helps or not but good luck and happy vacuuming lol.

Jim

[Harry Robinette]

Scott
I put my pump in a 3 sided top and bottom cart, I have a 5" fan behind the pump blowing across and out the open 4th side. It still get's really warm.
Let us now if you find some way to quit this thing.