Vacuum Pumps........again.......

Stuart Ablett

Member
Messages
15,917
Location
Tokyo Japan
Recently some half decent pumps are going on auction here for reasonable money, so I'm in the market for one, thing is they use Pascal (Pa) here for vacuum pump ratings, not the "Inches of Mercury" (inch Hg) like I'm used to.

I think, IIRC that I should be looking for at least 15" Hg, better to have closer to 20" Hg, right?

From what I can see, 1" Hg equals 3386 Pa

So say 18" Hg would be about 61000 Pa.

Now on the various websites I find here, they list this a 6.1 x 10-4

Sorry but my math sucks on stuff like this, does 5 x 10-4 = 50000 :huh:

Or some such thing, must be an "Engineer" thing I guess :rolleyes:


 
Geez I'm stupid :doh:

10-4 = 0.0001 right?

man these pumps are REALLY low pressure, what gives? :dunno:

g-100d.jpg

that means 5x10-4 is the same as 5 x 0.0001

Right? :huh: :dunno:

So 0.0001 x 5 = 0.0005 Torr or 0.00001969" of Hg........??????

Man I can pull more vacuum with a straw in my gob..

OK, I'm REALLY confused here, what would you need a pump that pulls so little vacuum for?

Something is out of whack here..............
 
Interesting page here - http://www.npl.co.uk/pressure/faqs/vacuum.html. Look at the table marked "Pressure Ranges". Smaller Pascal measure means "higher" vacuum (further away from atmospheric pressure). 5 x 10-4 is, on this scale, in the "very high vacuum" range. At 120l/min I would also think that this pump will not only pull a strong vacuum but do it reasonably quickly.

looks like a bargain to me.
 
A couple numbers that may help...

Standard atmospheric pressure is 29.97 inches of mercury, then you adjust for the altitude (about an inch lower for each thousand feet of altitude), then you adjust for weather... this is what the weathermen report ("barometric pressure is 29.45 and falling, prepare for a storm").

If you get rid of 28 inches of pressure equal to 28 inches of mercury, you have gotten rid of most of the atmospheric pressure... darn good. Not a perfect vacuum, but great for a vacuum bag (or most other things you want a vacuum for).

At sea level, the air weighs (presses down) at 14.8 pounds per square inch (most people round to 15 psi). So anything that doesn't squish must also push back at 15psi. If you get rid of 28/29.97 or 93% of the atmospheric pressure that was pushing back from inside the bag, then you end up with 93% of 14.8, x 144 square inches in a foot, or almost a ton of air pressure pressing down on each square foot of the vacuum bag.

In practice, you won't get that much vacuum inside the bag - but it is reasonable to expect 1500-1700 pounds per square foot.

Watch out for the psi readings. If you put a gauge in the air at sea level, it should read 14.8 psi, so you would spend a lot of time adding or subtracting 14.8 (depending on whether you were making pressure or vacuum). So most gauges are calibrated to start at 0 rather than 14.8 ... or actually report the difference between the measured pressure/vacuum and the atmospheric pressure at that point. This is referred to as psig or psi on the gauge. And you are right, that sometimes vacuum is just a negative number... how much below the 14.8 psi or "0 psig".

Now, it is up to you to convert to Pascals, stones, newtons, or whatever other unit is the local favorite.

Hope this helps
 
Found one, but I think it would be OVERKILL.........

d-650d1.jpg d-650d2.jpg
(that cart is it sitting on is nearly 3' long)
D-650D They want $300 for it, says......

200V 50/60Hz
CYCLES 50/60Hz
DISPLACEMENT 507/618ℓ/min <- That is 134/163 US Gallons a minute :eek:
REVOLUTION 950/1150rpm
MOTOR POWER 1.1kW <-1.5 Hp
OIL CAPACITY 1.8ℓ

Think it would work well for a veneer bag press :rolleyes:

200V would be a bit of a pain, and it is LARGE, I think I'll stick to a smaller unit...... :rolleyes:
 
What are you going to use it for? The guys who stabilize wood blanks for pens pull about 23 inches and it seems to work. The pen forums talk a lot about vacuum pumps. Same dilemma there, finding one that works well without spending a fortune. Old refrigerator compressors seem to work OK except they must run a long-long time to get results. But the price is right.
 
Frank beat me to the suggestion of using an old refrigerator or air conditioning compressor - with your talent for making tools, it should be a snap.

I believe they are not rated for continuous duty, so you would need a tank and controls. Joe Woodworker (www.joewoodworker.com) tells how and sells the odd parts if you can't find them locally... the tank is just some PVC sewer pipe.

I chose to go the way of a continuous duty pump (see post 1669 on Marty's shop thread) because it was smaller - not especially cheap, but I am not into DIY tools.
 
I thought about the old air-con pumps, I'm sure I could get one cheap, but it is my understanding the the coolant, the freon type stuff, is actually a lube in these pumps........ :dunno:

Dunno.

Cheers!
 
I thought about the old air-con pumps, I'm sure I could get one cheap, but it is my understanding the the coolant, the freon type stuff, is actually a lube in these pumps........ :dunno:

Dunno.

Cheers!

I haven't heard that issue, but since you are taking air out of the bag, not into it, I bet you could put a couple drops of oil into the pump air line occasionally, like you do with a nail gun.

Getting rid of the freon shouldn't be a problem. It has become so hard to get, that I have seen Air Conditioning men pump it out of old systems, and save it to use for repairs.
 
Not meaning to interrupt your post but I was considering a strong vacuum cleaner as a vacuum pump. Would a hard working sucker work as well" I know it will do the job on a vacuum press bag but wonder about a vacuum chuck for a lathe.... My new shop vac will suck the chrome off a trailer hitch but I was thinking of an old vacuum cleaner motor deticated to the task. any thought or info on this idea?
 
... Joe Woodworker (www.joewoodworker.com) tells how and sells the odd parts if you can't find them locally...
Gosh, wish I had suggested that!:thumb:


... the tank is just some PVC sewer pipe.
Actually, the instructions say to use schedule 40 or 80 PVC.

Incidentally, if you scan down the page of "Visitor's Vacs", you'll see the system I built. I used a refrigeration vacuum pump I picked up from a pawn shop for $100 plus a few parts from JWW.
 
I've had a good look at the Joe Woodworker site, great resource, but a lot of the stuff there is specific to the US, still great ideas! :thumb:

Steve, the shipping on that Vacuum pump is $131, so with the purchase price of nearly $90, that equals $221 or about 27,000 yen. If I can get something local for less, and have it 100V that would be great!

If I was in the US, that pump would already be on my lathe! :D

Cheers!
 
Not meaning to interrupt your post but I was considering a strong vacuum cleaner as a vacuum pump. Would a hard working sucker work as well" I know it will do the job on a vacuum press bag but wonder about a vacuum chuck for a lathe.... My new shop vac will suck the chrome off a trailer hitch but I was thinking of an old vacuum cleaner motor deticated to the task. any thought or info on this idea?


Bill, I hooked my "real" vacuum pump to my DVR lathe, and it worked fine. But my lathe "vacuum chuck" adapter suggested a shop vac, so I tried that, too, and it worked just as well. (I never got to a deep vacuum because of leakage through the bearing and head in the lathe setup, so the extreme vacuum of the vacuum chuck wasn't required, the shop vac was enough).

My shop vac struggles to get the bulk of the air out of my veneering vacuum bag, and doesn't come close to the degree of vacuum I want for glue-up work (bent wood laminations or veneer).

Beware of use of a shop vac... most of them use the airflow to also cool the motor, and will overheat if you use them to hold suction without airflow. I know my Fein has a separate cooling fan, and I believe the Festool does, too, but I know my Ridgid shop vac does not.
 
I tried the vacuum with the DVR and it did not work well at all, I could not even sand, let alone turn the bottom of the bowl.

Thus, I'm looking for a vacuum pump.
 
I tried the vacuum with the DVR and it did not work well at all, I could not even sand, let alone turn the bottom of the bowl.

Thus, I'm looking for a vacuum pump.

I was surprised at how well the DVR vac hookup did work.... so let's review what I did, and maybe can find why it didn't work for you. If you think this would be better as a separate thread, please use your Moderator skills to do it.

First, vacuum chucking won't work with very small pieces. If you are turning a piece with only 1 square inch outside surface, and had a perfect vacuum (you won't) it would only have 15 pounds pressure holding it on the face plate. On the other hand a 6 inch diameter plate (so I can use 2D math rather than 3D) would have about 28 square inches of surface, which in theory could have well over 400 pounds of force. Even at 50% effective vacuum, that 200 pounds is still ample for gentle cuts. If you have a 6 inch diameter bowl rather than a shallow plate, I think you will have the same force onto the faceplate - I bet the extra surface area will probably just contribute to forces trying to collapse the bowl sideways (but it has been a long time since those engineering courses).

As you know, the DVR vacuum adapater is just a bearing that fits in the headstock (held by a setscrew), and a short pipe that comes out of the bearing. That pipe has a hole in the side to allow airflow to your shop vac so that the vac doesn't burn up. A piece of masking tape fixed that hole... I have enough leakage in the hoses of my old vac, and my new vac has a separate cooling fan.

I installed a vacuum connector (like a tire air connector... air pressure hose connectors do not work for vacuum) in that pipe (to use with my vacuum pump), and also turned a piece of soft wood that fit over the pipe, the outside has a slight taper over which I can slip on my shop vac hose. Thus I have fairly good connections to either shop vac or vacuum pump.

For the vacuum chuck I cut a piece of 3/4 inch plywood about 10-12 inches in diameter and attached it to the face plate. I drilled a hole in the center, then turned the edge so that it would be balanced on the lathe. I found some "no slip" kitchen shelf lining that appeared to have closed pores (think a 1/8 inch thick sponge pad that was airtight), and cut a circle to fit on the plywood faceplate. At first I used some two face tape to hold it, then went to spray adhesive. Still need to refine the glue process, but once I am spinning, no problem.

Before the first use, I touched the pad with a pen, while turning slowly, so I have a set of concentric circles to help center the work.

I have used two techniques to mount the work. With the lathe stopped, I hold the work on the face plate, carefully centered on the circles, then attach the vacuum and go. Or I leave the vacuum loosely attached, and slide the work around until it is centered with the lathe turning slowly - when it is centered, push the vac hose on fully. Don't try to slide the work with full vacuum... it tears up the pad.

I doubt if even a fancy vacuum chuck would be as strong as a four jaw, but I have had no trouble taking gentle cuts and sanding. But the amazing thing to me is that the shop vac holds as well as the vacuum pump. Since I have a continuous duty vacuum pump, all the air moved to make the vacuum goes through the pump immediately, so it is vulnerable to sawdust contamination (dust plugs the protective filter). Therefore I usually use the shop vac on the lathe.
 
Top