Vacuum Pumps ?

[pdinter]

I want to get a vacuum pump to hold down material on a 4 ft by 8 ft techno CNC. I'm looking for advice on what size pump to get?

[crazy^millman]

A really big one. I am thibking you will need a pump that will pull atleast 3-5 astomspheres of Pressure. If wanting to hold that big of a piece I would also look at the size of the line in which you are pulling the vacum through. I would problay use atleast a 3" line and also give myself the ability to section off the table so you do not need to pull vacuum on a 4 x 8 are all the time if you do not need to.

 

Here are a couple Links:

 

Link1

Link2

Link3

Link4

 

 

There are all types of of Vacuum Pumps todo all kinds of things it really up to what you decides fits. I would talk to the people who make them tell them what you are trying to attempt and let give you the best fit for your application. Vacuum is a funny thing and you would be supried what as little as -30 psi can do.

 

[ 05-30-2004, 06:54 PM: Message edited by: Millman^Crazy ]

[Karl Oram]

Hey Pdinter,

 

Have your dealer put you in touch with some other wood shops using vacuum to hold down.

 

This process is very common and typically will have an MDF sacrafice board with a grid of holes

drilled thru. The MDF is also porous and helps with the vacuum. I would also get a tank to put in line to act as a resevoir this way you will find a smaller pump is required.

 

Talk to the guys Selling either Biesse - Thermwood - Mordibelli or even Anderson these all offer machine with Vacuum solutions so may be able to put you on the right track.

 

Hope this helped a little.

 

Regards

Karl

[Chris Rizzo]

Funny that this topic just came up...yesterday a friend gave me an air-operated vacuum pump. 100 psi shop air in one side, -27 inHg vaccum out the other. It's a small little unit that certainly won't work on anything big, but I'm dying to try it out on an order of some small parts we've got here. I've never worked with vacuum fixtures before, so we'll see.

Here's a link

[George_Gerhard]

pdinter

Could you elaborate a bit more on what material, you will be cutting, Is it furniture grade plywood, or is it the cheaper cdx ply that is badly warped. Becker makes good vacuum pumps, I personally like Kaiser I use these quite often for my customers they come in many diferent hp

This is a rotary screw type, it also is expensive

Another one is Decker this uses fluid to make the seal

 

rgds

George

[STKSHFTR]

This is my first reply to this excellent forum, so please bear with me; I,m employed in the wood furniture and have a few years experience with vacuum work holding. Unlike compressed air where a small leak in the general scheme of things is of no consequence, dealing with leakage in a vacuum system is. A large component of this is leakage thru a breathable workpiece. Furthurmore, vacuum measured in atmospheres never exceeds a value of 1 bar ( which at sea level may approach 29" of mercury or approximately 15 psi ). For these reasons workholding, as it relates to woodworking, becomes something of a balancing act. Place a 1 1/4" MDF workpiece (prehaps 2' sq.) on a breathable spoilboard and attempt to part it off in one pass with a 3" dia. cutter and you may end up finding it in the next county (even with a 40 HP vac pump) !! On the other hand, if you are cutting melamine clad particleboard with a 1/2" dia.bit on a well gasketed fixture, then a 1/2 HP pump may be all you need.

Generally, you'll want to size your pump to accomodate the largest workpiece you commonly run on fixturing that you are willing to replace fairly regulary. As a point of reference; we run the gamut of wood products on our 5 x 10 router (15 HP spindle), equipted with 2 - 9 HP pumps without problems. Much of the time 3 HP would be overkill.

My recomendation would be to buy a 1 1/2 to 3 HP rotary vane pump off ebay, do not run it through a receiver tank, valve it to cycle between 18 to 22" Hg, use 3/8" braided hose to your gasketed fixturing and cut some parts of two square or larger. Initially put a vac guage at your fixture to verify the values. After some experimenting, you'll begin to get a sence of what you need to work with before spending your hard earned cash on pump capacity you may never really need.

Lastly, I'd like to appologize for the length this and say that as a CNC greenhorn, I read this forum daily and have learned a great deal.

best regards

Marv

[MATT Q]

That is what this forum is for Marv welcome to the forum. Nice 1st post.

 

I would zone your vacumm areas also this helps in more holding power than one huge area cause if you get a little leak the part will lose all holding with a large area and reject part. I use the 1/4" round gasket and cut the track with the machine about a 1/4" from my trim and leave a little of the gasket sticking up above the surface

suction cups are nice too.

[Keith Graydon]

quote:

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Furthurmore, vacuum measured in atmospheres never exceeds a value of 1 bar ( which at sea level may approach 29" of mercury or approximately 15 psi )

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+1

 

And Welcome to the Forum Marv

[Harryman]

Go Marv!!

 

Welcome to the forum.

 

Conductance is a big deal with vaccum and it is proportional to cross section of the plumbing and also affected by length. I think that one 3/8 line on a 4'x8' fixture would be very short on conductance. Go big on the plumbing.

[Thad]

Marv,

 

Welcome to the forum! Way to jump right in there.

 

Thad

[crazy^millman]

Well cool I never knew that and the owner of a company I worked for use to always throw that out there for the Carbon Fiber molds that we use to do. I use to always ask him for that is psi and could never get answer that made sense to me.

 

Welcoem to the forum Marv

[George_Gerhard]

Good answer Keith

many people forget this fact, in high altitude locations it is impossible to obtain 29' hg. Places I have been to in Mexico, I was lucky to get 22" hg. The temperature is also a factor.

However as someone who works with cnc routers daily machines with large tables the idea of a 3/8 hose will never work. If you are looking to evacuate a 5'*10' area and hold the parts with flow through (that is the ability to put a waste sheet on the machine then hold your parts with the vacuum drawing through that sheet, no pre drilled holes.) If your cutting hard wood on pods, then that would work

 

rgds

George

[The Iron Chef]

quote:

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Good answer Keith

---

I was just quoting Marv. I agree withh him 100% tho.

So i gotta give credit where credit is due. way to go Marv!

 

 

-Keith the Iron Chef

[Travis_Buchanan]

You need volume & strength. We have 2 50hp Sulair pumps here pulling 3 routers. That is 2 5'x10' beds, 2 5'x6' beds and 1 5'x5' bed. Our vacuum is run throut the plant through 8" PVC. We get 25" Hg + consistently. But remember that no matter how strong the vacuum you still only have 15psi max pressing down on the part, so dont try to cut a 2" x 2" x 2" block out in one depth pass like most "engineers" think you can.

[MATT Q]

We have 13 four station rotary vacuum formers and 17 CNC trimming machines in the plant that I work in and we run the entire plant with 8 30 h.p. pumps, with 4" pvc line, and a surge tank on every rotary and an extra couple of tanks in the back of the plant just to give you an idea how the big suckers make it work:) and we hold 28" hg on a consistant basis have to have tight molded parts.