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  • Older threads on making a air table

    I was wondering if anyone knew where this older post thread was> I looked searched for it but couldnt find it?? thanx Mike

  • #2
    I know I made that suggestion but it may have been on PM and I don't go there under any conditions any more, PERIOD because of the Nazi running it.
    It's only ink and paper

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    • #3
      An air table or a vacuum table? There were a few threads on vac. clamping but I don't recall one on air tables.

      Steve

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      • #4
        My memory isn't perfect but I don't remember an air table discussion on this site either. There's been discussion of air bearing design on the Yahoo Quorn group and the basic principles should transfer.

        If you're not just blowing air up it's dress (which isn't really an air bearing) you'll need to make an arrangement of air distribution holes on the underside. These holes should have a slight recess dimple around them to provide a pressure area for startup and in the event the block is pushed down to the table by weight or force. That is, the air pressure (lb/in sq) times exposed hole and dimple area (sq in) equals the force lifting the table back up. Tiny hole equals tiny force.

        Then you also need to consider the size of holes feeding air to the underside. In order to keep the table on an even keel there has to be some differential force between one edge and the other to raise the side that's being forced down. If the holes are too large the ones on the raised edge can supply air to the opposite side resulting in zero righting force to get it back even.

        There are some places that supply a porous carbon that can be used for metering plugs but it gets pretty pricey. I think it can be approached empirically with some experimentation of hole sizes, some pressure gauges to see how pressure underneath changes with changing down force etc.
        .
        "People will occasionally stumble over the truth, but most of the time they will pick themselves up and carry on" : Winston Churchill

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        • #5
          Here is a link to a company that manufactures air bearings for all sorts of industrial applications. I work on machines that use hundreds of them to support a large metal belt that travels in excess of 180 MPH! These are a porous carbon design, where the entire surface of the bearing has a metered stream of air flowing out of it. They work very well, are very sensitive to contamination in the air supply, and are VERY expensive! A 2.5 x 12" bearing costs us around $200, and we use over 750 of them on one machine! The bulk of the bearings run at 70 PSI, but a small amount are supporting heavy loads, and run at 325 PSI. The high pressure ones are custom made, and insanely expensive. Some of their smaller, standard products are pretty reasonable.

          TGTool pretty much covered the main aspects of floating an object with air. One simple approach I have worked with, is to machine an array of "lands", or shallow pockets on the base plate of the object to be floated. Each of the lands are supplied with air through ports that are threaded, and have brass set screw orifices installed in them. This design works well, as it is a simple process to change the orifice size until acceptable performance is achieved. Precisely metering air to all lands is the most important aspect, to avoid oscillations, or simply tipping to one side, and losing all the air out the gap on the opposite side. Also, flatness and surface finish of both surfaces is very important.

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