Air handling, fitering etc. for air spindle bearings?

[PekkaNF]

I have been offered an used air bearing spindle. It is odd, because it has 1:10 speeder and 115 VAC motor. Not that cheap and it comes without air handling system.

I don't know much about these systems.

1) How do I check used spindle that the bearings hasn't been contaminated/crashed and that they are functional? If the seller ever has plugged them into normal shop air, is it a big no-no?

2) If I understand air quality requirements at all, they look pretty steep. Is there any "normal" components I can hook up and get away with it or it really is that specialized and the whole works needs to be specific for air bearings?
http://www.loadpoint-bearings.co.uk/about/how-air-bearings-work/

3) What sort of consumption/pressure would 57 OD diameter and about 350 mm long spindle have. WAG-value is a good starting point.

I may skip this now if it looks too chalenging. I try to learn one thing at the time, but this has several unknowns to me.


Thank you,
Pekka

[hanermo]

Some people have built them.
They used shop air, and they worked very very well.

The pressure needed was quite small circe 0.3-0.5 bar, and air usage is pretty low.
My wag, about 1/5 that output by a 2 hp std cheap compressor.

I think the cleanliness specs is so that very expensive spindles dont fail due to contamination even over time.
Just dry, and sort of clean.
Maybe an extra filter, or dryer, these are cheap bits, and thats it.

Its what I have seen .. but no real personal experience.

[PekkaNF]

Thanks. I just talked here one pneumatic systems designer and he knew about this stuff, but never ordered these components. Industry standard here seems to be 5 um, so prefilter is no problem. But 1 um oil separating filters and rest of the stuff is definately nonstandard and not available on local normal industry shops.

I'll try to find out a bit more, but if I can't easily find parts to make this work, I think I'm going to pass it.

Pekka

[NeoTech]

Been curious about larger air bearing applications, for like a lathe and such..  Seems so simple and bloody complex at the same time..

[hanermo]

Air bearings work well, for lathes.
They can be made very stiff, and very accurate.

And I have NO clue why they are not more common- probably just lack of new thinking.
There are videos on youtube of airbearings on lathes.

[NeoTech]

one of those airbearing spindeles from precisioninstruments, is round and about 45000-80000 euros.. ;)
you can sometime find a used one on ebay and in surplus stores for around 20000 euros.

If you not find and take care of a "crashed" one which usually means alot of grinding or relining it. =)

[SwarfnStuff]

Hi Pekka and all,
      I recalled seeing a thread on here regarding a build around this topic. This is the one.

  http://madmodder.net/index.php/topic,9283.msg103034.html#msg103034

An air bearing for his Floating End Mill Holder.

Regards,
John B

[NeoTech]

Yeah in a small application like that you dont really need alot of air.

[PekkaNF]

I decided to pass. It was build for 30000 rpm and 1/10 hp, bit fast and bit small for what I had in my mind. BUT I'd like to learn more about this technology.

Last ten years I have bumped into some air bearing applications. Real life and virtually.

First one was a laser interferometer measurement unit. That was impressive thing and ease to move "rock" on the way was incredible. I remember that measurement principle and air bearings were treated very cursory in the technical college, but very it wasn't something really unkown.

Then I have seen them on coordinate measurement systems, but everything about them is out of reach and also bit too involved.

Then I have seen articles about air bearings in conjunction of drill/endmill sharpening with TCG. This was first time, I think middle of 90's when I read some construction articles on US Home shop machinist mag (or something of that kind of title). Then I thought that maybe these can be build by HSM. Reading little bit further, but I still didn't got first hand experience. I do see here benefit of very low friction, which is the very reason on this application. But I had serious doubts about load carrying ability and stiffness.

It was't until Dan Gerbards YouTube clips I started to reconsider building "something".

The more I read about it, the more I see issues with it. I found one online calculator for load carrying and pressure/puck size and I think it had something on orifice size too. But even though underlaying idea is simple, real life product is not.

Then I got sidetracked and started reading about porous material pucks/sleeves....so far they look like most promising road for quick success. However I haven't found a source of reasonable price pads or bushes nor source for porous graphite to try make of my own.

I would like to test linear motion over granite surface plate. Just something for quick testing. Any ideas?

Pekka

[NeoTech]

The big problem ive had with this subject is getting my hands on enough brass to cast some of the bigger parts of a spindle.

[sparky961]

Maybe you can fins a bar (pub), have a few drinksdrinks, and play around with an air hockey table for a while.  Or is that just a Canadian thing?

[PekkaNF]

Those air hockey tables and most of that stuff has it all wrong.....

Normal consumer gets close to air spindles on hard drives and processor cooling fans. I did some more reading and there seems to be some issues that are hard to solve easily on DIY resources. Orifice type needs some real knowledge and experimentation, not to mention making orifices....but I have an idea on that one. Porous type would be a magnitude easier IF you had the porous (graphite) material.

Having low friction is one thing. Getting it stable and rigid/stiff is another altogether. Let's see, maybe I'll never get out of armchair with this topic.

Pekka

[Sid_Vicious]

I would like to test linear motion over granite surface plate. Just something for quick testing. Any ideas?

Pekka

The inventor of hoovercraft vehicles supposedly used a shoebox and a vacuumcleaner in reverse when he tried out his ideas. Don't know if it helps you with your idea?

[PekkaNF]

There is quite a bit of industrial applications where material is moved by applying a film of air underneath. This is to reduce friction. No concideration on how far and how stable the surface is moved.

Intended use of air bearings is a little different matter. Challenge is in metering and distributing correct air flow/pressure profile between two layers and keep them at nearly constant distance. Oldest for is to make two surfaces very flat and smooth and meter air flow with an orifice. Lifting tendency is moderated with an opposing similar arrangement.

There is a short application guide:
http://www.newwayairbearings.com/design/application-guide

Pekka

[PekkaNF]

Found some calculators.
http://www.tribology-abc.com/calculators/c12_4e.htm

Like this one too:
http://www.nelsonair.com/NA_primer.htm

Pekka

[hanermo]

I dont know, but read a lot about this and have the pieces already ..

Many working spindles have been made, by amateurs.

From memory, the hole needs to be about 1:1 - 1:2 in diameter-depth, and 2-3 x D of conduit.
Ie
conduit 1 mm. Hole 2-3 mm D, and 4-6 mm deep.
The hole acts like an air reservoir, and the pressure-cubed law makes it very stiff, as the air in the whole hole gets compressed.
Just like citroen suspensions.

With grooves, it was 2-3 mm wide groove, 4-5 mm deep.
2 grooves at each spindle end, in the approx 25 mm D sizes.
Seemed it does not much matter, on sizing.
Affects rigidity and efficiency, but wide variance seems to work, by several examples.

Did not need super small clearances .. just that smaller might be more efficient, as I understood it.
Ie air bearings work with both 0.1 mm and 0.002 mm clearances.