Interesting point about the ceramic bearings. Why are they so guarded about them? Hmmmm odd.

-Bob

I wonder if there are problems with the non-graphite porous air bearings. Several years ago when we were building the machine with the porous graphite pucks, New Way was pretty open about the ceramic air bearings — now it looks like they don’t want anyone to know about them.

Agreed, they are quite reasonable costs when you consider their performance and application in industry.
I had no idea New Way was selling ceramic version, amazing. Thanks for the link.

BTW, I have only recently found, to my delight, that NewWay have been posting very nice vids on YouTube;
http://www.youtube.com/results?search_type=&search_query=New+Way+Air+Bearings&aq=f

Yep, love the piezo motors myself. We can only dream of playing at the moment although I did recently find this actuator by Elliptec which does not require (apparently) a complex amplifier/driver;
http://www.youtube.com/results?search_type=&search_query=elliptec&aq=f

Cheers,
Bob

From my perspective as a system integrator, air bearing costs are already reasonable (given the cost of the rest of a high precision system). However, if you’re paying out of pocket for personal use, it’s a different matter.

New Way Bearings sells three types of porous air bearings: graphite, ceramic, and silicon carbide. Right now, they only seem to mention graphite, but if you google you can find part numbers for the others.

BTW, another technology that’s really cool and fits very well with air bearings is Nanomotion’s piezo motors. IIRC, it’s about $1000 for a motor and analog input servo amp — I’d love to use them at work, but haven’t found a good match yet (I can’t spec stuff just because it’s cool).

Yes I’ve been thinking about the replication idea you mention. No way around it, I’m going to have purchase at least an 18″ surface plate or parallel for that. Also thought about epoxy coating some steel for my guideways to cheat my way out of precision grinding. Looks like in reality I either I have to get them specially made from steel or I need to think about vacuum preloading. Float glass is another idea one I’m looking at too.
I have also seen the Axtrusion concept in your link, interesting idea.
I too have seen some patents and papers that show porosity is the critical variable and made vague suggestions of how it is adjusted. Sound quite laborious and somewhat explains their cost. Kudos for getting a hold of the procedure documents and Matlab sim! I’ve wondered too if it’s possible to use porous ceramic or even plastic instead.
For conventional bearings the only really useful info I found was this; http://www.nsc.co.jp/en/tech/report/pdf/n9304.pdf
It has dimensions of the layout and basic performance. I’ve wondered if laser machining could be used to make a copy if it was economical. Anyway all interesting stuff to think about, one day I would love to try it.

I recognize you daedalus from CNCZone. My nic is Zathras BTW.

Tony, thanks for the search link. I’ve found some prices for surface plates here and I’m looking at 2.5K for 39″ x 25″. Youch!

Cheers guys

I have done some research into running surfaces for such bearings, and one option that seems to be the best bet for low cost one off parts using epoxy replication.

This is a process where a mold release is sprayed onto a conventional surface plate, then the epoxy is poured with contact to the plate, the resulting surface is very close to the flatness of the granite.

You can also use replication techniques to attach the air bearings to the moving truck whilst maintaining parallelism between the truck and the track, without having to precisely machine the bearing mounts (see link).

Check this out, i think the approach has quite a few benefits: http://pergatory.mit.edu/perg/research/Cortesi/index.html

As for porosity, i have a mathematical simulation of a porous air bearing in matlab, and the critical value is porosity over thickness of the material. Also i have a step by step process for decreasing apparent porosity of the material, as well as measuring flow, this all used to be done by hand in the past.
The critical choice seems to be getting high enough porosity in the first place.

Poco graphite have a product called TM which looks like a good contender, i have emailed them to see if they have porosity information (there is a small amount available for two other products in their guides).

Tony, one improvement that would be very welcome here would be the option of email notification of further comments.

I am on CNCZone by the way, nickname is daedalus

Regards,
Tom

I’m always checking out eBay. Thanks for the links. I had a quick look but they don’t seem to ship to Australia. Besides, the weight is the problem when shipping Granite and The fact that they use UPS is the other problem, very costly indeed. I envy you guys! I have looked for some large Granite parallels for the axes to run on (4 bearings). Also trying to find some steel parallels for the guideway since I would need the bearings (2) to be magnetically preloaded. I need about 150mm travel on one axis, say 100mm on the other so I may need 18″ parallels to do it. The air bearings are large @ 2-1/2″ you see? God I’m starting to think “float glass” now. Anyway, just a little more patience & luck is needed right now. So close! Forum sounds like a good idea to me Tom. Can’t wait to hear more of your project too.

Also, as I’ve mentioned before, I appreciate all your updates; I am very open to adding new ways to keep in touch to this site (such as improving the comments, mail lists, forums, or such).

On the porous bearing I have, I was extremely lucky to have purchased 6 of them from an engineer in the US who actually designed ultraprecision machines ( http://www.precitech.com ).
He was interested in my project and graciously decided to sell what he had to me. That’s the only way I could possibly afford these babies. Luck! He also sold me 7 other non porous bearings as well. Some of them had been obviously crashed and repaired and I hope they still work OK as I’ve had no chance to test them yet. Until that time, I had considered making them (porous or slot) myself. This engineer I mentioned suggested that it is possible to make them with EDM graphite but admitted that he never managed to find out what type it was. One can never have enough bearings and I’m still thinking of trying one day. But as you point out Tom, where can one find porosity info of these materials? The prospect of being able to make them is irresistible though.
Anyway, my biggest challenge with these air bearings will be trying to get a surface plate of some description. They are no where near as cheap here as in the US sadly. I’m getting desperate now and considering table top Granite. Tried self leveling Epoxy but doesn’t seem to be anywhere near as good as promised.
Many challenges (and money) ahead!