milling with vacuum table

[TREV]

morning all,

 

i have some aluminum parts aprox.1"x4"x.187thick

what is the feasability of using a vacuum table to hold them down? we need to do lots of these

parts and i want to be able to set up a large group at one time.

not a bunch of heavy cutting but it needs to be

secure to make me sleep at night

 

so any one with expeirence using vacuumes please advise

 

thanks,

trevor

[Guest]

Vacuum chucks can work, if there is a fair bit of radial milling, you may be able to design a chuck that uses vacuum and hold down tabs with screws, that can be machined off at the very end.

[TREV]

john,

thanks,

 

what i was thinking is my first set up would be in a vise. at that time i will be putting some holes in the parts, the second set up would do work on the opp. side so i thought about having posts standing on the vacuum table to locate and

help keep parts from potential shifting.

how much vacuume pressure would i need to be looking at, ballpark number wise?

[Guest]

14.7 lbs per sq/in is going to be about the best you can get./ A mercury gauge would be a 29.9 inches. 30 being a perfect vacuum

[TREV]

john,

 

thanks alot.

i will let you know how i make out with this project.

 

trevor

[35K chipper]

trev,

i use air venturi vacuum generators for my vacuum fixture plates. they create about 22>25 in of mercury at sea level. i use as many as i can just in case i loose a part i don't loose the whole table. i get the generators from reed supply.

they are cheep and coolant won't weck them.

 

35k

[Rob @ Target Machine]

+1000 For the venturi pump.

 

I use them for .015"-.062" 4047 Alum laser weld covers. The venturi pumps create way more vacuum than the centrifigul pumps, and like mentioned, are "coolant safe". I can't say how many times I've cleaned out a centrifigul pump.

 

You can buy O-ring stock by the roll for sealing the edges of the part shape, and use standard O-rings for sealing around thru holes.

 

You can drill the thru holes, M00, add screws, then finish in one operation if all the work is on one side.

 

Beats using double sided tape if you are going to make alot of parts.

[K10LT1]

Are there any sort of guidelines or rules of thumb for vacuum fixturing. I had a nylon job that was 1/2" thick and about 12x3". I figured that there would have been about 12in.2 area inside the o-ring it come out to like 120-180 pounds of force holding the part. Would this be enough to keep the part from moving while side milling and drilling from the side (on a tombstone in a horizontal). Also is it a must to have a constant supply of vac. from the pump to the fixture or would a vac. resivour be suficient to hold the parts for the machining cycle.

[35K chipper]

K10Lt1

I'd still pin it to keep it from being pushed when you drill. the vacuum venturies i use are mounted to the plate and always on. remember when you have a vacuum any coolant in the area under vacuum will boil ie out gas even at room temp and there goes the vacuum. not good!

 

35k

[Superman]

A++ for having it pinned / dowelled,

as they stop the sliding action, vacuum stops the lift ( all axes are controlled )

 

Thin irregular forms receive tabs with location holes in a previous operation. ( depends also on surface area for the vacuum )

We also create a 2" grid ( approx with 0.08" ballnose X 0.01" deep ) on the vacuum surface to get an even "suck", and use a 0.2" soft foam type o'ring for the vacuum boundary ( 80% depth ). O'rings are used but as they are harder may need 90-95%, and can push back.

 

All machining is completed up to generating any holes using vacuum ON, Over clamps used with vacuum OFF, to generate holes, part can be removed for inspection and replaced ( with no loss of position ) , then tabs removed to finish the part.

[Toonz]

(shaking head) You metal workers....trying to work like woodcutters.....

 

OK....first your parts are quite small, and even a large vacuum pump will have a hard time holding them down depending on what operations you need to do to them. Can you describe a little more detail of what you will be doing?

 

Aside from that, potential options include masking off unused area of vacuum table spoil board, taping all edges of parts to increase vacuum. Reduce feed rates use smaller dia. tools.

[Guest]

quote:

---

You metal workers....trying to work like woodcutters.....

---

Some of us have been VERY successful using a vacuum system, it's not just for wood.

 

[35K chipper]

i cut metal parts on a boss3 bridgeport under vacuum! i am sure that was way before you wood people had cnc routers. so who's trying to be like who?

 

35k

[Rob @ Target Machine]

quote:

---

i cut metal parts on a boss3 bridgeport under vacuum! i am sure that was way before you wood people had cnc routers. so who's trying to be like who?

 

35k

---

True...I've been doing this for 20 years. As small as .300 x .300 square by .008 thk lead shim stock.

How else would someone hold something like that?

[RobertELee]

And us "metal workers" are capable of making our own vacuum tables without having to buy overpriced boards with small holes in it.

 

[Rob @ Target Machine]

Yuppers.....2 minutes to write a toolpath for the O-ring grooves.

No biggie.

 

BTW We have one of those vacuum fixtures.

 

The layer of dust on it is 10 years thick. LOL

[35K chipper]

the machines that make cnc routers are metal cutting machines mills, lathes, grinders! did i say grinders? way to much precision.

 

35k

[bogusmill]

We are machining 24" X 48" aluminum coupons for a customer from 8" thick to .300 through the center to test heat treat in center of thick aluminum. Also for 2" thick SS and Ti64. We hold it with a venturi pump on a Fadal 8030 and a vacuum table about the same size as Fadal table.

[35K chipper]

24 X 48 now that really sucks i think about 16000 lbs. worth. now that will hold it!!!!!!!

[K10LT1]

Anybody have any advice for designing a vac plate. I have some designs that I would like to perfect before the opourtuinity to make them ever comes around.

[b_bengineer]

I have been building machined parts for 20 years in Vertical and Horizontal mills using vacuum!!! Most of what has already been discussed is what I've used, venturi vacuum generators, build your own fixtures with a grid pattern, pin or sink your part into fixture, adjustable rails to slide in and capture part. The product I've had the best luck with is called flap seal. It is a square shaped rubber gasket with a "flap" on it. You mill a " precision" track, cut and fit the gasket into the tack, silicone the ends together, introduce vacuum and CUT CHIPS!!

--------------------

 

Ben Benjamin

[#Rekd™]

Hi,

 

What type of material and cross section of orings is the most used or suggested? What type of glue is used for splicing (crazy glue)? What type of hose or line is being used to transfer the vacuum from the pump to the vacuum chuck?

 

Any photos or sketches of vacuum chucks that are being used?

 

Thank you in advance!

 

John

[b_bengineer]

The gasket material is flexible black rubber (buy it by the foot) Dunham Tool Inc. - I don't know why they don't advertise it? Contact them though - they sell it, or I can provide contact info where I buy it through a rep. It is square by nature with a small flap on top. You machine a defined width and depth groove and push the seal into it, no glue to hold it in place. Cut the joining ends and silicone seal them togther. The flap faces OUT away from your vacuum area. When vacuum is introduced, this little flap raises up meet your material and provides an effective seal. The hose I use is braided rubber hose from McMaster. I also use a tank from Dunham that collects coolant that may get by your seal occasionally. The vacuum unit is installed on top of it, and on opposite end of line so coolant doesnt get to the vacuum unit. It will collect about 2 gallons before it needs to be emptied.

 

Hope this helps

 

Ben Benjamin

[Bob W.]

I buy my vacuum seals from Mitee-Bite and it works really well. My vacuum system (self built) has a sub plate that stays in the mill with interchangeable top plates. I have a generic top plate with a grid pattern (.16" wide x .125" deep grooves for seals) and several other custom plates for specific jobs. When designing a plate there needs to be another groove just inside the sealing groove to allow the air to get pulled out.

 

If there is just the sealing groove with the o-ring and a hole in the center you will not get good results. I had originally tried this and had a big problem with lifting around the edges.

 

I use my vacuum chuck all the time but there are a few things I really look out for. I typically use smaller cutters that can't really throw the part if vacuum is lost. Imagine losing vacuum with a 3" face mill at 4000 rpm in a heavy cut :-) I also use it only for larger parts. The best you can do for hold down force is atmospheric pressure (14.7 psi?) no matter how good the vacuum pump is.

[Rob @ Target Machine]

Bullet Bob - I have pumps that can pull air through .015" stock. Originally used for Helium Leak checking hermetic housings, they definitely "Hold" better than the standard pumps.

 

Unfortunately they are too powerful. They will deform .062 thk stock. So I guess you could say "they really suck". LOL

 

If you don't already have venturi pumps, they really are ideal. They hold better than "Standard" centrifugal pumps, and are impervious to coolant "pull through".