Vacuum Fixturing

[Adam123]

I have zero experience with vacuum chucks.

 

I was hoping to start a discussion about the ups and downs of various methods. An issue I'm concerned about is how much ability does a vacuum plate have to pull a plate down flat once it reaches a certain thickness compared to size. I have a 3/16" thick plate that is 8.5" x 7.5" wide. I can have anywhere from .006 to .012 bow or twist in the stock. Will I have any problems pulling it down flat?

 

I see the various models that are available. Any favorite brands? I was even thinking about the benefit of making a custom vacuum plate that is job specific.

[FROZEN]

http://www.miteebite.com/products/vacmagic_vm100_i.html

 

Check them out. I have never used a vacuum chuck, but they look cool.

[Newbeeee™]

Big thing you got to remember about vac chucks, is they don't necessarily get the parts flat.

Parallel yes, but flat not always.

If you have a bowed billet and suck it down, then machine, as soon as you let the vac off it can bow straight back.

Flip over and vac down and machine, and vac off, and the part can stay bowed.

But parallel

[Adam123]

Thanks, Guys. I'm expecting the part to bow back but I want to make sure I can draw it flat because there is a local check that runs the perimeter which needs maintained. if the part is bowed and twisted while machining it throws the dimension off.

[civiceg]

3/16 plate will pull down no problem with that small bow over that large area. You start to have issues when the part is cupped over a small area. +1 to what newbeee said. But you can go back and forth between mechanical fixtures and a vac fixture to achieve flatness. We always make job specific vac fixtures. It allows you to maachine a pocket to not only locate the part but also to make sure it does not slide.

[Adam123]

That was actually the route I was thinking about, making our own. It looks like it would be pretty easy. The gasket material, is it standard or do separate suppliers make proprietary gasket material?

 

Civicegg, do you guys buy the gasket material in large rolls?

 

The other question is the pump. I've seen both the electric pump and also the cheaper one that you hook up to an airline. Is there an advantage to either? Our shop air is reliable. Besides our machines go down too if our air goes down.

[civiceg]

I hate the air/vac venturi blocks, because of the reason you mentioned. Yes machines will stop too, but if your part is mid cut and there is no solid locator, you lose position. A few summers ago we had 5 machines with them running. Our air compressor hated the extra load. This was a 100 hp compressor, but it runs the whole shop. 

 

I prefer smaller electric pumps that do not pull a whole lot of cfm for each machine. We have catch tanks inline with the fixtures to collect coolant that gets by. The vacuum gauge is also on these tanks. A large cfm pump will not show a drop in vacuum at the fixture because the pump draws so much. You could put a gauge on the fixture, but with coolant and chips its not ideal. Oil less vane pumps also are nice. Makes for no mess and no real maintenance.  Unless the operator has a leak and fills the 7 gallon catch tank and gets coolant in the pump. 

 

We buy foam sponge cord by the roll, 100/200 feet at a time in all different sizes. There are hundreds of different routes you can go with gasket material. Foam cord is ok, but coolant gets to it eventually and it swells. Depends on the job on how often it gets changed. If it swells too much your part will be sitting on the cord and not the fixture, not good.  I think vacuum fixtures are great, but there are some learning curves on how you set it up. Size of gasket, how much it sticks up, how you cut the vacuum grid.

[THEE THAINZ™]

I've used "o" ring material before and it also works very well. You can cut a groove with a ball endmill about 60% depth for the diameter your using. Just buy a roll and cut it to the desired length and glue together.

[Newbeeee™]

If you use neoprene sponge cord, cut and glue with something like Loctite superglue (or 406 if we're talking 'engineering adhesives' )

We never use ball nose either - just square bottom cutter and for a 4mm dia cord, we use a 4mm cutter and go 3.5mm deep.

Because it's sponge you don't get compression set and can get away with a size for size cutter/oring (obviously if you were using a solid nitrile type ring, then this won't work).

[Tim Johnson]

I hate the air/vac venturi blocks, because of the reason you mentioned. Yes machines will stop too, but if your part is mid cut and there is no solid locator, you lose position. A few summers ago we had 5 machines with them running. Our air compressor hated the extra load. This was a 100 hp compressor, but it runs the whole shop. 

 

 

What compressor are you using? We used to have 2 Ingersoll 75 hp compressers that would run at around a 80% load together and 2 machines running vacuum fixtures would overheat them. We switched to two 100 hp Sullairs and now with only one running we have a 25% normal load and around 30% load with two vacuum fixtures.

 

We use surgical tubing for our fixtures.

[civiceg]

It wasn't just the vacuum fixtures causing an issue, 20 or so machines and respective operators using air. Not to mention other departments also using air as well, weld, assembly, paint etc. I don't know the brand but it just went up last week after almost 2 decades of use. Probably about four years ago we switched over to dedicated electric pumps for each machine. 

[Guest]

http://www.miteebite.com/products/vacmagic_vm100_i.html

 

Check them out. I have never used a vacuum chuck, but they look cool.

I've personally used them and they do work well. Extremely versatile. I was bummed when we had to give it back. (Was on loan for a tool show).

 

+1 on square corner for o-ring grooves. It gives the o-ring a place to swell before affecting part height. I use the ball e/m for air passages though.

[jeff]

Anyone got a ballpark price range of those mitee bite vacuum chucks?

[T_MALENA]

I've used quite a few of them here.  Made all myself except for 4 of them.  Also used everything from large vac pumps to the air pressure venturi style. The vac pump is the way to go for any type of production &/or expensive stuff.  What I mean by that is all of the vac pump styles, the oil ring type the venturi type even a hand one will all be a max of 28-29 inches of Hg. The diff is how much free flow CFM they have. So all the pumps rated at 28 in of Hg will have the same holding power. The venturi style will have a harder time pulling down a out of flat part because its not flowing enough air(venturi styles are typ 10-20 cfm max) so you wont feel the air sucking past a "leak" in the seal. Now a vane or oil pump, like what I have here, will have the same vacuum of 28-29 in of Hg BUT if flows 250cfm. I have taken out of flat parts that are 20"x20"x.6" and laid them on the vac table and even though they were not sealed it still held the part!  So the smaller the cfm the less leakage you can have.

 

Hope that all makes sense.

[Newbeeee™]

^^^100% correct + good analogy ref the large cfm for the initial pulldown/seal.

.

we use these 5cfm which work well for us

:http://www.ebay.co.uk/itm/JAVAC-AIR-CONDITIONING-A-C-REFRIGERATION-VACUUM-PUMP-CC141-/400027351660?pt=LH_DefaultDomain_3&hash=item5d237cfa6c

[Adam123]

At this point, I'm leaning towards building my own but does anybody have any experience with Pierson's products?

http://www.piersonworkholding.com/vacuum-chuck.php

 

I'm planning to use their air powered vacuum kit plus their gasket material.

 

 

[shazam/TPP]

check out these guys, we bought the large plate and doing some dynamic milling in some 7050 aluminum. holds it down no problem.

 

http://www.piersonworkholding.com/vacuum-chuck.php

[Adam123]

Shazam, are you using the air powered vacuum unit like I linked above?

[shazam/TPP]

yes we are the 13.5 x 20, inexpensive compared to the others. working good thus far.

[Adam123]

Just to be clear... you are using this...

 

[Newbeeee™]

If using a vacuum, you'll need a water separator. We use one of these fixed to the vac pump http://www.ebay.co.uk/itm/DIESEL-FUEL-WATER-TRAP-SEPARATOR-ASSY-DEEP-BOWL-TYPE-CAV-296-FUEL-FILTER-/281569178560?pt=LH_DefaultDomain_3&hash=item418ed4b3c0

Coolant WILL get sucked through at one time or another and this will protect the pump.

[Adam123]

According to the guys at Pierson, their shop air driven vacuum pump can handle both coolant and minor debris passing through it.

[shazam/TPP]

that's exactly what we are using on our Fadal vmc 4525.  we actually connected it directly into the machine where the fourth axis plugs in, there is a push on fitting in the back upper right of the machine. we turn it on with M60 (air brake) and then just use the valve after that to turn on and off.

[Adam123]

Awesome! Shazam, you and everyone else has been super helpful!