Double Sided Gasket vacuum Fixture

[diyengineer]

[nomedia="http://www.youtube.com/watch?v=GwUKAydYLaA"]YouTube - Double Sided Vacuum Clamp.avi[/nomedia]

Above is the double sided concept.

I would like to use gaskets like these:
All Star Adhesives - gasketing products for CNC routers and v-groove tape for v-grooving and coving applications

My table size:
The tables overall length is 178" (y axis).

The width of the table is 82.5" (x axis).

The table is made out of flat aluminum that the gasket should suck down to nicely.

I would like to do small production runs.

I plan on cutting .063" aluminum sheet. I will nest many pieces onto a 48"x144" sheet. Each "piece" will have a small gasket that holds the item in place. this fixture will also double as my spoil board, since i will be making the same exact parts, it wont destroy anything. I was told a much smaller vacuum pump/s can be used with this gasketed fixture method, and also allow me to swap out different fixture for different runs. If you look at the second picture i attached i would gasket each part like that, but the rear of the fixture would have a overall gasket to suck it to the table.

I currently do not have a pump at all. I have $1100 dollars to put towards a pump.

I need help selecting the best pump for the $$.

Just a few options i have found for pumps.

Grainger

Regenerative Blower: $986.00
Blower, Regenerative - Regenerative Blowers - Air Compressors and Vacuum Pumps - Pneumatics : Grainger Industrial Supply

Vacuum Pump: $738
Evacuation Pump, 1/2 HP, 9.53 CFM, 3440 RPM - Vacuum Pumps - Air Compressors and Vacuum Pumps - Pneumatics : Grainger Industrial Supply

MotionTek
Regenerative Blower: $381-$584 (USD converted from Canadian)
Vacuum system table Air blower pump holddown CNC Router Canada USA

Harbor Freight
Vacuum Pump: $99
Electric Vacuum Pump - 2.5 CFM

Vacuum Pump: $149
Air Conditioning Vacuum Pump - Two Stage, 3 CFM

Air tanks: 11 gallon $34.
11 Gallon Portable Air Tank

I'm limited to single phase 240VAC (amperage doesn't matter), and $1100 dollars. I also can acquire 100 gallons (or as much as needed) of air tank storage for holding surplus vacuum for faster fixture "snap down".

Thanks for all the help!! Shoot me any pump/info that you feel is necessary!
I don't know much about those pumps or how to compare them for what i will need.

[ger21]

You might want to look at the Joewoodworker site and build your own pump system. Joe Woodworker - Woodworking, Vacuum Pressing and Veneering Information Website

From my experience, it's very difficult to hold thin, flexible material with vacuum. To get a good seal, the gasket needs to compress a little, and if the material is too flexible, it won't compress evenly, which causes leaking.

[LeeWay]

That material can also cause chatter in aluminum.
I experimented with a small vacuum block using an old air conditioning comp. It isn't man enough for the job, but would have worked okay if it always maintained a perfect seal.
I didn't use the gasket like you intend though. I had one guy doing some work for me cutting .125 aluminum by hand using a router and the gasket seal method that held the stock to the template. It worked great, but he was just profile routing. Not through cutting and the seal never broke.

Can't help with the pump type, but in this case, bigger is better I think. It needs to be able to recover almost instantly from an incidental leak. To do that it needs volume. I think the air tank will help there.

[Geof]

In my opinion none of the ones you list would be ideal.

The bottom two have a cfm rate that is too small, they would not be able to handle any leakage. Also the ultimate vacuum they develop is way more than needed down in the micron range.


The regenerative blower from Grainger develops a maximum vacuum of 70 inches of water. Don't get fooled by this number. It might sound impressive but full vacuum is equivalent to about 384 inches of water. Seventy inches of water is worthless as a vacuum for holding purposes unless you are dealing with entire 4 x 8 sheets of plywood.


In the specs for the CNC Router Vacuum System Air blower I can find no mention of the vacuum it develops. Being a blower it is probably as worthless as the one from Grainger.


The Evacuation Pump, 1/2 HP, 9.53 CFM, 3440 RPM is getting closer with 9.5cfm and a vacuum of 25" Hg but I think it would be marginal.

Using good gasketing this one would hold your full sheets of very effectively because you will have a large total surface under vacuum. Once the parts are separated it might be another story judging from the apparent size and shape of the parts (if I am interpreting your picture correctly) and the parts may slide sideways or lift if you do a perimeter cut using a cutter with any helix.

Actually looking at your parts they may have insufficient surface area for holding by vacuum no matter how good your vacuum is.

The maximum holding pressure per square inch using vacuum is one atmosphere, approx 14.7 lbs per square inch. Less if you live in Denver.

To get this holding power you need a perfect (un-obtainable of course) vacuum of 30"Hg (To be picky it is 29.something). Low volume good quality vane type vacuum pumps will give you this sort of vacuum but at a fairly low cfm so they cannot tolerate any leakage. With these pumps even a pinhole leak can overcome their cfm capacity so they cannot develop any vacuum. Low cost pumps with a higher cfm rate will probably develop less vacuum but will be able to do so with leaks that would overcome the better vacuum rated pumps. Realistically you cannot expect to get much better than 27" Hg unless you have an enormous pump. This vacuum is equivalent to about 13 lb per square inch of holding power. If you have this acting on a square foot of surface you have an impressive 1900 lbs holding the material down. If the material is rigid it will be very difficult to lift or slide with this type of holding force. However if the material is flexible it is not difficult to peel up and edge to create a leak and then the entire holding force is gone. Naturally when you start moving to smaller areas the total holding force is reduced and this is when sideways movement becomes a possibility. The cutter exerts the same force whether it is running a cut down the side of a piece one square foot in area or five square inches. But the five square inches is only held down by about 65 lbs of force so it slides sideways.

Do your parts have holes? If so you may be better off considering holding them down with screws. You could use a low vacuum to hold the enter sheet of material down onto a sheet of 1" MDF spoilboard for drilling all the holes. Then insert screws while the vacuum is still on and finish cutting them all out. The cut tracks in the MDF would actually serve as vacuum channels for the full sheet meaning you would be able to get by with low vacuum rather than having to suck through the spoilboard.

[diyengineer]

Those are not my exact parts at all, it was just a fixture that used gaskets the way i intended to.

My parts will be fairly square and a bit larger like panels. 20"x20" etc.

.063" 6061-T6 is fairly tough stuff, its tempered so it doesn't flex very easy.

I saw a guy online use shot filled bags over each part on a large surface to hold down his sheet to get the initial suction. He also used a large air tank to hold the vacuum. I saw another guy throw a 1/2" sheet of surfaced plywood ontop of a sheet so he could get some weight ontop of the sheet and grab suction.

For doing this type of work i could use a reverse style end mill (hope thats correct) to push the material down, instead of lifting it up. I could also use the direct over the spindle mobile clamping from widget works, pictured attached. They have successfully cut out .010" aluminum just by using that attachment alone (and double sided tape i believe).

I was also thinking i could use a small amount of petroleum jelly or alike on the gasket seals to help with the sealing. I would obviously have to ask the provider of the seals if this is necessary, and would it benefit me in anyway.

Is there a way to calculate my side forces i will produce onto the aluminum?
Spindle is capable of 24,000 rpm, i will use carbide tooling probably less than 1/8" in diameter and 2 flute, and i will probably cut the .063" in multiple passes (2-3).

If i cut a panel that is 6"x6" that has 36 square inches, that should give me 36 square inches x 14.7 pounds per inch= 529.2 pounds of down force.

That sounds more then realistic to myself since i'm going to machine this stuff in multiple passes.

I'm shooting All star adhesives an email to see what there thoughts on the matter are.

[diyengineer]

$488.25
Evacuation Pump, 1/2 HP, 7.0 CFM, 3440 RPM - Vacuum Pumps - Air Compressors and Vacuum Pumps - Pneumatics : Grainger Industrial Supply

2 of these would give me 14CFM, for $976.
3 of these would give me 21CFM @ $1464.75

Ideally if i already had my "fixtures" made i could calculate the air volume inside and then know how many cubic feet of air i have to remove correct? That would give me some ballpark time on when it would snap down, assuming a perfect seal. By using a large vacuum storage tank/s (which i think i will have to use, not a problem) it would give me a greater volume of air removal to snap down the fixture.

[Geof]

It is not likely you will ever 'snap' things down using only a pump unless the pump was huge. Which is then overkill once things are snapped down. A tank is almost essential and also a large bore valve between the tank and the vacuum fixture so the initial flow is a real surge not a dribble.

One of the Dayton pumps with a decent sized tank is likely to work okay if you can get good sealing.

Using a down helix cutter is debatable in aluminum because it does not clear the chips as well.

All those ideas to hold the sheet down for the initial grab work. Also just taping around the edges of a full sheet will provide a total seal and the plate will pull down and the gaskets take over the seal.

Petroleum jelly on the seals will help but then chips stick to it and are a pain to clean off.

Don't use 14.7 for your calculations you will never get that differential pressure. Be conservative and use 12psi. Which still gives over 400 lbs on a 6" square.

You can probably guess that your sliding friction coefficient will be better than 0.2 so your 400 down gives 80lbs side resistance. . . probably enough that a 1/8" cutter would snap before moving the part.

[diyengineer]

Thanks Geof. Any input is highly appreciated.

How many gallons would i need out of a tank? Could i get by using multiple 11 gallon tanks all connected to 1 valve through a manifold?

Good idea about the tape around the edges.

It is not likely you will ever 'snap' things down using only a pump unless the pump was huge. Which is then overkill once things are snapped down. A tank is almost essential and also a large bore valve between the tank and the vacuum fixture so the initial flow is a real surge not a dribble.

One of the Dayton pumps with a decent sized tank is likely to work okay if you can get good sealing.

Using a down helix cutter is debatable in aluminum because it does not clear the chips as well.

All those ideas to hold the sheet down for the initial grab work. Also just taping around the edges of a full sheet will provide a total seal and the plate will pull down and the gaskets take over the seal.

Petroleum jelly on the seals will help but then chips stick to it and are a pain to clean off.

Don't use 14.7 for your calculations you will never get that differential pressure. Be conservative and use 12psi. Which still gives over 400 lbs on a 6" square.

You can probably guess that your sliding friction coefficient will be better than 0.2 so your 400 down gives 80lbs side resistance. . . probably enough that a 1/8" cutter would snap before moving the part.

[Geof]

If your manifold has large diameter connections then several tanks ganged up are equivalent to a single larger tank. I can't really predict how much volume will be needed because again it all depends on how much initial leakage you have until the gaskets start making a full contact seal.

[lgalla]

Fixtures and zoneing is probably the best way to go if your pump is small.If you use a grid,it can be the first thing you route.Sorry I only know how to use the full table vacuum with the huge pumps.
I use a Bush R5 pump which can pull near 29.7Hg.At this negative pressure it will crush the air tank you are looking at.I think propane tanks can handle the negative pressure.
Larry

[diyengineer]

Fixtures and zoning is probably the best way to go if your pump is small.If you use a grid,it can be the first thing you route.Sorry I only know how to use the full table vacuum with the huge pumps.
I use a Bush R5 pump which can pull near 29.7Hg.At this negative pressure it will crush the air tank you are looking at.I think propane tanks can handle the negative pressure.
Larry

WOW crush the tank huh? That is some intense vacuum. I would want to buy a cheap tank just to see it crush, that would make for a sweet video!!

I will run up to home depot and get a price on a large empty propane tank. I think they sell 20 gallon up to 150 gallon. I could always call airgas, im sure they have some type of spec they are good up to.

I wonder what kind of manifold i would need.

[LeeWay]

I have seen some large table use only 5 or 6 inch PVC for manifolds. That would hold a good volume of air and be far less prone to collapse than a cheap tank.

They then run zones off that main with valves for each. I have seen several different styles of these back when I was researching them. I think the bulk was on Youtube. Some where here at the Zone.