homebuilt vacuum press pumps?

[Andy Maldoror]

does this look like a decent pump for a vacuum press?
anyone know what the cfm is?
http://cgi.ebay.com/Gast-Vacuum-Pump...#ht_500wt_1142

[Andy Maldoror]

or is there a specific pump i should look for?
i can't afford the $320 for the gast 5.5 at joewoodworker right now...looking for a good alternative.

[Ben Hatcher]

A vacuum pump isn't going to draw a lot of cfm. What you're looking for is what kind of vacuum it will draw and this one said 24 hg which if I'm not mistaken is more than enough for doing veneer work. If you want a cheap/home brew version, find an old dorm fridge. As long as the compressor works you can use it as a vacuum pump. Just make sure you put the suck side into your bag

[Josiah Bartlett]

The refrigeration vacuum pumps at Harbor Freight are a pretty good deal. I have the 3 cfm version:

http://www.harborfreight.com/two-sta...ump-66466.html

I've used it to service my car A/C system and a couple other things. It pulls a good vacuum and you can safely run it for 90+ minutes at a time without it getting too hot.

[Andy Maldoror]

i was thinking more along the lines of gast or thomas model pumps...if there were specific models. i want to build something that will last for years for large sheet veneering and for some lutherie work.

[Will Blick]

Is there a reason why you would not buy a pump from some of the veneer vendors....I would think there pumps are proven well for this application?

[Bruce Wrenn]

Check with a couple of HVAC places. When their pumps no longer pull into the micron range, they are basically trash. A new pump is almost always cheaper than a rebuild. You could also use a venturi pump, operated by your air compressor. Check out the AVR093H ($30 plus shipping) from Air-Vac Engineering. This is the venturi that most of the premade systems are based upon. If you can find an old AC compressor (Borg Warner, York, Tecumshie sp?, Ford), these make excellent vacuum pumps. I'm refering to the two cylinder vertical kind. My first air compressor used one, and after thirty years it is still going strong. Because it has "Ford style service valves," I can "backseat" them and use it as a vacuum pump.

[Frank Drew]

Is there a reason why you would not buy a pump from some of the veneer vendors....?

Price; if you can find a good, used vacuum pump, as I did for $75 (some years ago admittedly), why pay retail?

[Andy Maldoror]

to be clear...i want to build a auto-cycling vacuum press along the lines of Joewoodworker's kits. something that will be quiet in my small shop. and something that will pull down 4x6 and smaller panels, lutherie work and form bending.

looking at the gast and thomas pumps on the bay there are a few that look like what i'm looking for, but the specs aren't listed and i was having trouble matching up the model numbers to the spec sheets listed on the gast website...probably because the pumps i'm looking at aren't being sold new anymore.

are there any specific models in piston pumps that anyone's had experience with or knows about that i should look for in a decent quality pump? i'm looking to spend around $100 or more depending...
if no specific models, what are the specs i should look for? just the Hg?
double pistons better? i need something quiet for a small shop connected to a retail store...seems like some of the pumps i've seen are probably pretty loud, but don't know how to tell.

thanks for the suggestions so far. i don't know much about salvage fridge compressors and if they'll be strong enough...auto cycle...quiet..etc. can they pull down 4x6 sheets with enough pressure? and i don't want to use venturi.

i actually have a cycling vacuum pump connected to a vacuum dry mount press in our picture frame shop, but sharing isn't going to be practical.

[Bruce Wrenn]

A rotary pump will be the quietest. HVAC pumps aren't that loud. You can buy vacuum control switches. You could do a set up using an air tank from a compressor as a reservoir. Look at a cheap compressor, like the 1.5 HP unit from Sears, often on sale for less than $100. Disconnect outlet line from compressor. Then remove inlet filter. Loosen barrel of compressor at the crankcase and turn whole assemble around. so what was inlet is now outlet. Reconnect lines to tank. At tank, remove guts from check valve. Replace pressure switch and gauges with vacuum switch and vacuum gauge. Instant vacuum pump.

[Dave Bell]

Here is everything about the Diaphragm Pump you need to know.

http://www.gastmfg.com/pdf/diaphragm/specsht/maa.pdf

Dave

[Dave Lehnert]

I have always been a little confused on vacuum pumps and such.

Is there not a valve or the like that one could just hook up to a standard shop air compressor. Not buy a vacuum pump with motor and all ?

[Jamie Buxton]

There are two salient specs about vacuum pumps: inches of mercury, and cubic feet per minute.

The inches of mercury is a measurement of how much pressure the pump can make. Basically, anything called a vacuum pump will produce enough pressure for a veneer press. There are applications where the difference between 28 inches of mercury and 27 inches is a big deal, but for a vacuum press is doesn't matter. It is just a few percent difference in the clamping pressure.

The cfm spec is more relevant for a vacuum press. A higher cfm rating means that the bag pumps down more quickly, and it means the pump can maintain good clamping pressure when the bag is a little leaky. Pumping down quickly is important if you use PVA for your glue. You want to get the piece clamped before the glue sets up. If you're using urea-formaldehyde or epoxy, which are slow-setting glues, speed matters less. Maintaining clamping pressure against leaks is quite useful. All bags develop leaks with time. They collect schmutz in the sealing surfaces, or get little holes punched in them by workpiece corners.

I veneer objects which are components in furniture, and have two bags -- a 25"x8', and a 50"x 9'. I find a 3 cfm pump is a good size -- mostly for the resistance to leaks. I also have a smaller pump that is probably less than 1 cfm, but is much quieter than the big one. I use it when I can.

[Andy Maldoror]

jamie...good info.
i've been looking at the gast 72R...the 5.5 cfm sold by joeww.
do you think that could be overkill?
basically what i'm doing is restoring a vintage airstream style camper trailer and i need to make the curved veneered walls.
i read that bent laminate stuff larger than 4x4 or so probably needs a 5.5cfm.
in my case i'll probably be clamping it flat and bending the whole bag over a form rather than putting a form inside the bag.
after that large project i'm mostly only going to be building 3 ply laminate body guitars and probably never anything bigger than 4x4.
so is the gast 5.5 too noisy and powerful for that?
also, can you regulate the Hg so i don't get too much vacuum on my smaller porous laminate projects

[Jamie Buxton]

i read that bent laminate stuff larger than 4x4 or so probably needs a 5.5cfm.

As I said above, the cfm mostly has to do with resistance to leaks. If you can keep the mouth of your bag clean, and it is 50" wide, my experience is a 3 cfm pump works.

in my case i'll probably be clamping it flat and bending the whole bag over a form rather than putting a form inside the bag.

That's a good plan.

can you regulate the Hg so i don't get too much vacuum on my smaller porous laminate projects

You can run a vacuum press with a pump that just runs all the time. That's what I do with mine. You get whatever pressure the pump produces. Or you can buy/make a controller. It acts like a thermostat, except for vacuum. It senses the pressure inside the bag, and turns the pump on or off at pressures that you set. Probably that Joe Woodworker site can sell you a complete controller, or sell you the parts for you to make one.