support method: floting

[ML1]

for some time I have been thinking of my own cnc-machine. and while thinking and discussing with a frend and theacher we came up with a idea.
Instead of used standart bearing and rail, whe want to construct a cnc machine with is floting on air or oil.

the priciple is simple you take two plates. one is the tabel witch moves, the other is a groundplate. in the tabel you drill a lot of tiny holes (0,1-0,5mm) en trouch those holes you pump air or oil. so the oil or air creates a film between the table and groundplate. so what you get is a table with little friction, and it can withstand a lot of force, becease It cant bent becease it is supported at al the surface.

please give me a reaction what you are thinking of this idea, or maybe there are already cnc machines build in this way....

Gr. Maarten

[trubleshtr]

what will move the "plate"??? how will you maintain positioning without rails? A plate on a ball screw alone will deflect and bend under cutting force. Can you provide more information on your idea???

[ML1]

all this was just a idea, and really didn`t have much time to think about it, or make drawings.

to guided te plate, I have two options: 1 is to use standard ball bearings on the side and top of the plate so the bearings keep the plate down and centered, and the second option is to use the system( so the air or oil film) also on the side`s and on the top.

personaly I like the first one more, but no doubt that I come up with some more solutions.

and to move the plate I was thinking of using a toothbelt. not sure yet.

but I do`nt have time now to make some drawings, maybe tomorrow otherwise sunday. and I want to make a test. just a small size steel plate,drill some holes, put some air between it, and see what happens. results probaly sunday.....

Gr. Maarten

[jkeyser14]

There are air tables that exist. They use air to keep the table flat and motionless. One of the teachers at my school has one in his lab for research, he does a lot of work with MEMS, which is basicallly mechanical engineering on a nano-scale. So he needs a table for his instruments that doesn't move or vibrate. I believe the table was about $50k when bought commercially, and it runs on tanks of Argon.

I'm not quite sure what the benefit of this would be on a mill, since the mill itself will cause huge vibrations. Even if you decouple the table from the mill, the bit will transfer vibrations and a lot of loads.

[jkeyser14]

They also make air bearings. They are the coolest things on earth. Check them out if you ever get the chance.

[cncmek]

Take a look at a CMM.

[DareBee]

Air bearing systems are pretty cool but my vote for cool has gotta be Mag-Lev.

[CNC Pro]

When I was in school, we had a cylinder boring machine that used a cushion of air to position the upper 1/2 of the machine (about 1000-2000 pounds).
It was two polished surfaces with air channels machined in one of them. It work very smooth, but had a range of motion of only a couple of inches at best. And once the boring bar centered over the center of the bore, the air was turned off and the weight of the machine kept it place.
I wonder how much air would be required to keep a cnc machine aloft thru a machine cycle?

[ML1]

I`m not woried about the quantity of the air. I only was wondering if somebody of you guys ever have seen/ heard of such a thing. but not in the profesional buissnes, I don`t want to spend a lot of money to it.

I still havent made a test, really didn`t have time, but I will keep you posted.

And what sre you thinking of oil instead of air. I thought it was called a hydrostitic bearing.

Gr. Maarten

[jrc347]

I think a liquid would be best. How about using a mini- water bed as a prototype. the liquid would have to have a fixed volume so the machine can "sit" on top of it.

liquids cant compress - air does

[ESjaavik]

You will need a carefully measured amount of air to each pocket. The cheapest way is to use capillary tube chokes. But how to calculate the airflow and make it happen is not easy. Start with buying a book on machine design. It will probably lead you to a method more suitable for a hobbyist. Look for cast resin bearings instead, they have very nice properties. And can be done with amateur means. They are even superbly suited for refurbishing old worn machines.

[HuFlungDung]

You still need some sort of rail to guide the motion of the machine elements, there is no getting around it.

You'll still need a mechanical feed system (such as a ballscrew or rack or belt or chain) to maintain cutting positions against cutter forces and mechanical feedback to determine positions (such as encoders or scales).

But, it is practical to make air bearings for the rails, to eliminate having to use rolling carriage rails.