Vacuum Chucks.

To All:

I was just wondering how common the use of vacuum chucks on a milling machine is, and what might be some of the advantages over other methods of holding parts.

Reply to
BottleBob
Loading thread data ...

BOB-- Vacuum chucks are used quite a bit in the woodworking industry, ceramic indusrty, as well as a few others. They work quite well "IF" they are designed correctly and the seals are propeerly installed. The only issue I have seen is the if the seal starts to wear it can slowly leak reducing the holding power. I would not hesitate to use them myself. BTW-- Yes I am the same one you hace called, I just changed my e-mail addy.

Neal

Reply to
Neal

We use them every day. It allows us to do a part complete in one operation, all edges, and the top. These parts are made from 1/4" 6061 plate, and are full of holes. The gasket pattern has donuts around the hole pattern. The shop is plumbed with 1" pvc for the vacuum system, and the 1.5 HP pump is in the compressor room. Each machine has a vacuum tank made from 4" PVC with end caps. Plastic tube acts as a site glass, and coolant can drain back into the coolant tank every N parts. Another 4" pvc tank in the compressor room is the final protection from slugging the pump. It will hold at 25 inches of vacuum even with a small leak. The customer supplies and Shears(!) the plates. (non-negotiable) The plates have so much warp in them that the fixture can't be flat. maybe .060" I use a piece of UHMW 1" thick, and can warp it enough to grip the plates, I can't pull them flat and hold them. We've made tens of thousands of these, and tried dozens of compositions to get the right grip for the gasket, along with dozens of base designs before we got it to work as good as it does. One limitation is variablitiy of the material. Sometimes it is too "gummy" and the feed rates need to come down so that the endmil doesn't push it loose from the fixture.

I can't quite imagine a quicker or cheaper way to make these parts. Our quote was way less than the competition. We tried very briefly to clamp the parts, and use multiple clamps to machine the entire rim. TOO slow.

The tool paths are carefully planned to minimize side loads in the part, to keep it from "squirming" The holes are all interpolated, we can do all the holes in the time it would take to do a tool change, and we can compensate each hole, more accutrately than drilling them. The compensation is critcal since there is a certain amount of "squirm" on the fixture.

We also use vacuum for a lot of other parts, since we have the system plummed right into the shop, and into each machine.

I have a few aluminum plates made up with a waffle grid, that can take rope gasket material for any size or shape odd part.

Sometimes I use the vacuum not to hold the part, but to hold it flat. I made tons of aluminum parts that were milled to a large, thin, flat section in the middle. They were clamped down, and a vaccum was pulled under the part to hold the flat thin section flat, and not pull up from the end mill. This allowed... more feed rate! A bunch more stuff I can't think of right now. Pete

Reply to
Half-nutz

Pete:

What size are your parts?

I wonder if you couldn't put a couple of holes in the plates first in another machine an install some pins in your vacuum chuck to locate in the holes so you could increase your feed rates to the maximum without having to worry about the parts "squirming".

Reply to
BottleBob

Bob,

Sounds like much too personal a question....

Reply to
PrecisionMachinisT

When this job hits, all machines are tied up. For weeks. The "squirm" is in the tenths.. But, it is a consideration. Fer example, we tried soft neoprene, for a gasket. Parts could not hold tolerance in the .0005" for the hole size. And we push the endmills to point of either breaking, or moving the part. Lots of parts to do. The chuck needs both sealing and traction. They are 12" X 13" Pete

Reply to
Half-nutz

We use one for production, cutting foam cores. We use another for flat parts that can't be clamped effectively. We have a couple of smaller ones used primarily for small foam prototypes.

Advantage- air pressure holds your part in place, precluding the need for tooling tabs or clamps or screws or bonding agents.

Disadvantage- only air pressure is holding the parts, so you better not get too crazy without working up to it.

Should I say we've been known to cheat and screw the stuff down until the very last?

Later,

Charlie

Reply to
Charlie Gary

Beats screwing the stuff up...esp if it happens at the very last...

Reply to
PrecisionMachinisT

ftp.machiningsolution.com/DSCF0007.JPG

1' Dia. 1" DOC 400 IPM at .900 step over. I'd have taken deeper cuts, and did - 1.75. once I was into the part. Hannita WaveCut end mills work pretty well in aluminum. I roughed three parts and gave the tool to my customer to try out. They will probably cut the first .250 or so off the end.

On this particular part I had to insert a support under a big counter bore -

8 inches more or less - in the back to keep the chuck from collapsing/crushing the part. Do the math. I'm pulling and holding 29 inches and no, I'm not talking about my schwantz. Sucked the part down an eighth of an inch or so the first time I turned it on. I had four dowels in the material in the picture here. The vacuum connection is in the back of the chuck between the chuck and the bolster plate. I just silicone'd in a piece of pipe in a pocket cut between the plates. My pump does 5 CFM so leaks between the plate faces aren't a problem and the pump on this job runs with the vent open so coolant aspiration isn't a big issue.

The real need for a vacuum chuck on this part is the floor thickness and parallelism call out - .060 thick parallel to the back plane of the part within .002. Piece of cake . I cheated!

If you are wondering, the stock is 32 inches square. I'd post the project but that would probably be trouble if you know what I mean, and I'd like more of this sort of work from the customer. They take a casual interest in the doings here at AMC. LOL

Needless to say, I recommend magnets and vacuum clamping for just about everything except small stuff that hasn't much surface area.

Reply to
John R. Carroll

I have only used Vacuum clamping on a CNC lathe, turning Rubber and Polyerethane etc. in to seals.

Works fine, as long as there is enough vacuum.

Reply to
Petersen_Michael

I wonder if anyone has ever tried placing a milling machine in a pressure vessel to machine parts? With a pressure of 100 to 200 psi in the tank your 'vacuum' held parts wouldn't be going anywhere!

Gary H. Lucas

Reply to
Gary H. Lucas

PolyTech Forum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.