Vacuum Chuck

[Rob B]

We are presently trying to make a vacuum chuck. I have done a search for this topic here on the forum but not really getting any answers to my questions.

My boss is engineering this "vacuum plate" with no idea of truely what it takes to work. Can you guys give me some pointers.

 

We have machined an alum plate that is 4" thick with cavaity machined 2" deep and all cavaity's are interecting each other. I've got a top plate that is 3/4 thick that screws to the top. This "top plate is what I'll be machining my part on. We have an o-ring between the main body and the top plate. We have a vacuum pump that was used to pull vacuum on an AC unit. Will this work or will this get me "KILLED". Next what kind of air hose should I use? We got a settling bowl to catch coolant that we are going to put between the vacuum plate and the vacuum pump. What kind of fittings should I use?

 

Basically can you point me in the right direction before my boss gets someone hurt. Is there any web sites that I can go to for info on this subject. Any and all help is needed.

 

Thanks

Rob

[Surface]

Is you boss's name Alcoa?

[Rob B]

No. Does it sound like ALCOA?

WE are a small job shop.

[Surface]

That was my attempt at humor.

4 inch aluminum plate with a 3/4 top plate. I don't think I could afford to make a vacuum table from that. It's perhaps a little overkill.

What are you trying to hold?

[Rob B]

It was humor. We have ALCOA in our backyard. Thought that was what you were making refernce to.

[summit fever]

Rob-

 

Sounds like you are going in the right direction. We use vacuum fixtures all the time, and set some of them up the same way.

 

One thing to change in the future: you don't have to make your vaccum cavity so deep. We usually use a 3/16 ballnose and make 'veins' within the shape of the rubber o-ring.

 

By the sounds of it, the vacuum you are using should work. Having the coolant bowl is a great idea.

 

If you want to get fancy with it, you can also add a ball valve with an air line fitting on it, and reverse the pressure with a regular air line to "float" the plate for easier handling.

 

The lines we use for vacuum are the hard plastic type used for pneumatic machines. You can also use the fittings for these lines on your setup.

 

If you need pics, email me and I can send some to you.

 

Cheers

[Bruce Caulley]

www.horst-witte.de

[Keith @ Solid Code Solutions]

Cool stuff Bruce!

[RObert TImby]

Rob,

 

I had work with a vacuum plate a lot. All I've to say do not let your boss talk you in to using different sections or chambers to vacuum the part down like what happen here. Before I can here they made a vacuum plate to hold this production part down and it was made out of alum. also but they made it with 8 different chambers that sucked the part flat. the problem is the alum. would warp ever time we use it so we have to skim the fixture ever time we use it. Also, use a foam O-ring it work great. the surgial 0-rings are not to coolant friendly, and make sure you use a coolant bypass before you get to the vacuum pump so you don't fry the pump.

 

Rob

[Rob B]

summit fever

 

you've got mail

[summit fever]

Rob-

 

Back at ya.

[summit fever]

Mail and pics have been sent to those of you who wanted them.

 

Cheers

[b_daddy]

summit fever

 

you have mail

[Guest CNC Apps Guy 1]

For the O-Ring Groove(s), I usually used a .1875 Dia. Flat E/M to machine the channel the for the o-ring. I use O-Ring Stock from McMaster-Carr in .250 Dia. I usually went about .220/.225 Deep so the ring would compress and decompress as I loaded and unloaded the part. Good ideas so far.

 

Good luck.

[#Rekd™]

Hi,

 

What vacuum pumps are people using? 1 or 2 stage and what level of vacuum and how many Liters/min are required?

 

Thank you

 

John Ford

[summit fever]

We use a two stage vacuum at 10 - 25 in. Hg.

 

Depends on the setup.

[#Rekd™]

Hi,

 

Which make of two stage pump, edwards, welch, leybold, varian...?

 

John

[summit fever]

The tanks have been painted over, so I can't tell you the name.

 

In the past we've used the Norgren venturi style also. Kinda noisy, but they work for some of the very small setups. They'll pull up to about 15 lbs.

[LT_mechead]

I don't have experience with vacuum chucks but with any o-ring the size of the groove and the o-ring material is important. If you are using conventional o-ring stock (not foam) do a search using "o-ring face gland seals" or similar wordage. The Parker O-Ring handbook contains a wealth of information on material selection and design data.

 

With a vacuum seal on a rough or uneven surface go with the softest material you can get. The softer material will conform to the sealing surfaces better. At vacuum chuck pressures you shouldn't have to worry about the o-ring extruding itself out of the gap. I do like the idea of using foam o-rings, they are less picky about the sealing surfaces but they may be too bulky in tight areas.

[Jerry Crofoot]

We use a square cross section O-ring material sold by Vac-u-lok. (vaculok.com) and had good success with it. The square cross section allows for more surface area for a smaller groove width in the table. The foam material compresses easy and comes in different thickness. There is a grade for coolant applications and a non coolant. I would suggest installing a vacuum gauge that the operator can see or a vacuum safety buzzer that will warn you if you’re losing vacuum. We normally have 28” hg vacuum and try to stay above 15 when cutting through the material exposing the air vacuum holes.

[MLS]

We use a .125 e/m to cut the seal grooves then follow it up with a .156 dovetail so the rubber doesn't pull out.

 

The rubber we use is advertised at .125 dia, but is around .150 dia generally. Works well...don't know where the heck they get it though.

 

The fixtures we build are standard nest fixures with a bleeder groove pattern in the top about .020 deep. We plumb the fixtures individually...which means we have a fixture for every part that needs vacuum

[Bruce Caulley]

We use a Witte Claw pump. Have a look at the link I posted above. It is a wet pump and as such it doesn't mind sucking up coolant.

 

Bruce

[b_daddy]

New to this whole arena of vacuum chucks, so I have a few questions?

 

How big of parts do you guys run on the chucks?

How well do they hold the part down and wht kind of machining can you do without moving the part?

[Jerry Crofoot]

The larger the vacuum surface area of the part, the greater the holding. So for small parts, I start with a larger piece of material just so I can have enough vacuum surface area to hold the part. If I need to rough the O.D. profile, I keep the cutter up about .020-.030 from the bottom of the part and therefore do not losing vacuum and holding power. The last thing I do is finish the O.D. profile. If I’m afraid the part will move on the finish O.D. pass, I add tabs between the part and the excess material. By adding indexing pins and pusher blocks to your vacuum table you can hold the material from moving side ways and the vacuum only has to hold (suck) the part down.

 

B_daddy “wht kind of machining can you do without moving the part?” We machine heat treat 15-5 stainless steel using high speed machining techniques with rough and finish feed rates over 100 IPM. The key is getting enough vacuum surface area and blocking the material if needed.