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Vacuum Table

Kaza

Plastic
Joined
Oct 13, 2015
Looking to build a low budget vacuum table, will be using it for 0.125" aluminum and plastics, mostly engraving very little contour end milling. The table itself is easy enough to design and build I need help with choosing a vacuum pump. I'm pretty sure a 9 cfm 3/4 hp is way too big for my applications. Table size would roughly be 13x13. Anyone have any input on what I should look into?
 
I can tell you what not to buy- any oil-type high vacuum vane pump used for lab work. They're designed only for high vacuum work and will send out oil mist if allowed to run at higher pressures for any length of time.
 
A simple vacuum pump with a 1/20 hp motor will do as long as the part remains sealed to the table for the entire process.Maybe $200.00. The Piearson unit uses a simple venturi to generate a vacuum from compressed air. A continuous supply of compressed air, not sure of the cfm requirements. I can tell you that if you look at what is inside that unit you will realize that $50.00 worth of parts can do the same thing.
Are you running wet or dry? If wet then you will need an inline tank to catch any coolant that gets by your gasket.
 
A simple vacuum pump with a 1/20 hp motor will do as long as the part remains sealed to the table for the entire process.Maybe $200.00. The Piearson unit uses a simple venturi to generate a vacuum from compressed air. A continuous supply of compressed air, not sure of the cfm requirements. I can tell you that if you look at what is inside that unit you will realize that $50.00 worth of parts can do the same thing.
Are you running wet or dry? If wet then you will need an inline tank to catch any coolant that gets by your gasket.


Sure, in our line of work you can always make instead of buy. If you have more time than money go ahead and make one.

With the venturi you dont have to worry about coolant. It exhausts with the air.
 
If you're going to use a venturi system I recommend doing what some local shops around here do: Run the venturi into an empty propane tank or similar vessel and use that as a vacuum reservoir so you don't need to use the cfm all the time. A couple ball valves or a push button to break the seal and you're golden.

We use a multiple HP, vacuum forming table pump that is total overkill but we never need to worry about flow.
 
The inline catch tank can help to seal the part.
With the plate vacuum valve closed, you build a "reservoir" of vacuum in the tank.
When you open the valve, it helps to slap the part down and form a seal before you have enough leakage to lose your vacuum.

So, getting the part sucked down, or a leaky gasket are the only reasons for a bigger pump.
An electric pump will be much cheaper to run than the venturi, and maybe cheaper to buy...

I got this pump from Ebay from one of our members here, for much less than a venturi solution.
It supplies vacuum to all the machines in the shop. Thanks again Gary.

PN 4299K7
McMaster-Carr
 
Those of you using venturis, what kind of vacuum numbers are you seeing? I know my two stage 5cfm rotary vane pump will pull 29", and I need every bit of it. Everything I use it on is sealed very well though... most setups will hold 28"+ overnight.
 
Those of you using venturis, what kind of vacuum numbers are you seeing? I know my two stage 5cfm rotary vane pump will pull 29", and I need every bit of it. Everything I use it on is sealed very well though... most setups will hold 28"+ overnight.

No clue. As far as I understand it the venturi works entirely on atmospheric pressure difference. area X 14= lbs of pressure. It won't hold anything once you kill the air.
 
Those of you using venturis, what kind of vacuum numbers are you seeing? I know my two stage 5cfm rotary vane pump will pull 29", and I need every bit of it. Everything I use it on is sealed very well though... most setups will hold 28"+ overnight.
Depends on what you get. I use the 28" model using .5 CFM at 60 psi, just because that works for me. Being the control freak that I am I buy the venturi and make the rest. Photo on the left shows the venturi from Vaccon with the body. Photo on the right is the assembled unit with a back to use without bolting to the fixture, the square brass is my first attempt at a valve. It is far more refined but I don't have any new photos of it. I went this route after finding out I couldn't disassemble the Vaccon body to clean it out, and if you screw the NPT nipple too far you will drive it into the venturi section damaging it. I think the venturi cost around $20, cute aren't they?

From what I have read about my 2 stage oil filled pump DO NOT use it with coolant!!! You are supposed to change the oil after very little use anyway and using it with any water it will ingest it since water will boil away at those vacuum levels. I use the 2 stage pump to degas resin. I used to use a rotary vane pump at my last employer but dealing with keeping it from ingesting coolant was a total PITA. Venturi pumps are not perfect but I think they are by far the best compromise for part holding on a VMC with coolant.







Vac-4.jpgVac-3.jpg
 
Here's a photo of what it looks like now. The body block has a built in valve, holds the venturi body, and measures 5/8" x 7/8" x 1-1/4". Red tube is air, clear tube is the exhaust/muffler. It takes about 2 minutes to pull it all apart to clean and lube.


Vac-5.jpg
 
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Those of you using venturis, what kind of vacuum numbers are you seeing? I know my two stage 5cfm rotary vane pump will pull 29", and I need every bit of it. Everything I use it on is sealed very well though... most setups will hold 28"+ overnight.

I have two of the Pierson units and based on my cheapie gage from mcmaster (McMaster-Carr), it pulls -28"Hg. Although, once you turn if off, your vacuum is boned. Gasket cords don't seal perfect, plus the air just goes backwards through the valve. I suppose a check valve there might improve, but the fixtures I use leak too much.
 
The inline catch tank can help to seal the part.
With the plate vacuum valve closed, you build a "reservoir" of vacuum in the tank.
When you open the valve, it helps to slap the part down and form a seal before you have enough leakage to lose your vacuum.

So, getting the part sucked down, or a leaky gasket are the only reasons for a bigger pump.
An electric pump will be much cheaper to run than the venturi, and maybe cheaper to buy...

I got this pump from Ebay from one of our members here, for much less than a venturi solution.
It supplies vacuum to all the machines in the shop. Thanks again Gary.

PN 4299K7
McMaster-Carr

I like that approach, and having a larger tank already at vacuum sure makes the parts suck down fast. With the venturi I'm using, it can be a bit slow if you have a lot of dead space between the valve and fixture.


Do you run coolant on the parts you're running with your vacuum? If so, how do you go about emptying it if the vacuum is always on?

I've found coolant running through the venturi pretty much kills the vacuum on my setup, and then the parts move around. I use a little jar on the table to catch coolant, if the fixture is leaky. It works great at maintaining vacuum, just don't forget to empty when it's near full.

20160909_211852.jpg
 
Sure, in our line of work you can always make instead of buy. If you have more time than money go ahead and make one.

With the venturi you dont have to worry about coolant. It exhausts with the air.

I make my own venturies because I usually need several thousand over the course of a year. Smallest one uses .4 cfm and generates 27" minimum from 100 psi. They will pull 27" at 70 without filter, but as the nozzle opening is .016 it takes very little to clog it, hence the inline filter.
 
I'm very glad I went with the vacuum pump over a venturi setup after reading all of this. Plumbing a reservoir before the pump eliminates coolant issues (I used a 3 gallon air tank and mounted the pump right on it). Ball valves at the fixture, before and after the reservoir lets you service the system from any point without completely shutting it down. And I'm betting my vacuum pumps' 1/3hp motor running all day uses less electricity than a large-ish venturi kicking my 7.5hp compressor on and off all day.
 
I'm very glad I went with the vacuum pump over a venturi setup after reading all of this. Plumbing a reservoir before the pump eliminates coolant issues (I used a 3 gallon air tank and mounted the pump right on it). Ball valves at the fixture, before and after the reservoir lets you service the system from any point without completely shutting it down. And I'm betting my vacuum pumps' 1/3hp motor running all day uses less electricity than a large-ish venturi kicking my 7.5hp compressor on and off all day.
I don't really notice my 4 hp compressor running any more using the vacuum pump, maybe it cycles 2 more times a day but goes an hour between cycles anyway so no big deal. It is true that compressed air venturi pumps don't work very well pulling straight coolant but a little doesn't bother mine. What you see bolted to the pallet receiver in my last photo is all of it, no tanks, no reservoirs, no extra crap and clutter. I push the knob in and I have full vacuum in about 3 seconds, pull the knob and I can remove the pallet right away. With foamed o-ring cord stock in a good fixture I never have a problem getting it to seal, even bowed parts. If I just want to use some rubber sheet on a flat plate then my little venturi pump doesn't flow enough and the rotary vane pumps would be the way to go.

Is your 2 stage pump an oil bath? If so does it not boil the coolant away in the reservoir?
 
If I just want to use some rubber sheet on a flat plate then my little venturi pump doesn't flow enough and the rotary vane pumps would be the way to go.

DavidScott, nice setup! I might do the same. Q: why would this not work for holding down a sheet of rubber? Also, what size venturi did you use? I'm seeing sizes from 60-150. I was looking at the Pierson, but if I can make my own, I will.

Configure Product On Vaccon Co., Inc.
 
I got a venturi off amazon for $19
, took it out of the enclosure and routed the exhaust back into the coolant tank.

Pulls 24"hg and uses 4 cfm of air at 90psi. It works but is loud. I bought the cheapo venturi as a quick "proof of concept" test before committing to a production level setup. I was testing a multi part fixture for small flat parts. Lots of good ideas here. I'll probably end up going the pump route to knock down the noise level.20200420_180534.jpg
 








 
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