My bearing castings were a little rough. Corroded too. I was hesitant to
clean up much of the "rough cast" in the middles of the top
and bottom halves of the air bearing, as I read a looong time ago (Lumley?) that that very roughness helped by making the air more turbulent. As that memory is vague at best (I wasn't even doing analog at the time) I opted to not mess with that rough cast, thinking I could always clean it up more later. Turns out it works pretty well.
However, the wide surfaces that make contact when there is no air pressure can be cleaned up with good results. I used jewelers rouge on the flat surfaces and spun the top plate relative to the bottom plate to effectively polish those surfaces. Grit from fine sandpaper would work as well, but it's important to not sand them, you need to use the powder/grit/rouge between the plates to insure they stay consistently flush relative to each other. That seemed to allow it to float with less pressure, however it requires the table to be level
to do so efficiently and effectively. It will obviously still run at higher pressure as before, but it's not as critical to have the higher pressure to float the platter.
I also drilled and tapped two more holes in the base at 120 degrees apart the same distance as the original air inlet from the center to spread out the incoming air more evenly. That requires a little more drilling/relieving from the underside of the chassis to run the split hoses to from underneath. Make sure to re-level the bearing relative to the table upon re-assembly. Check to make sure the rubber washers between the bottom plate and the table are in good condition while you're putting it back together- you'll need them supple to take up the difference when you level the bottom bearing plate. Although a bit rough and crude, the original design wasn't too bad, but can be improved upon in these ways.
If this is "clear as mud" you can email me outside the forum.
I haven't contributed much during this thread as it has been concentrating mostly on fighting the original air arm
which I don't use for some of those same reasons. I do think the 'nolls are a neat platform that can be used as a
quite capable table, for pennies on the dollar compared to cost no object tables.
RFG
clean up much of the "rough cast" in the middles of the top
and bottom halves of the air bearing, as I read a looong time ago (Lumley?) that that very roughness helped by making the air more turbulent. As that memory is vague at best (I wasn't even doing analog at the time) I opted to not mess with that rough cast, thinking I could always clean it up more later. Turns out it works pretty well.
However, the wide surfaces that make contact when there is no air pressure can be cleaned up with good results. I used jewelers rouge on the flat surfaces and spun the top plate relative to the bottom plate to effectively polish those surfaces. Grit from fine sandpaper would work as well, but it's important to not sand them, you need to use the powder/grit/rouge between the plates to insure they stay consistently flush relative to each other. That seemed to allow it to float with less pressure, however it requires the table to be level
to do so efficiently and effectively. It will obviously still run at higher pressure as before, but it's not as critical to have the higher pressure to float the platter.
I also drilled and tapped two more holes in the base at 120 degrees apart the same distance as the original air inlet from the center to spread out the incoming air more evenly. That requires a little more drilling/relieving from the underside of the chassis to run the split hoses to from underneath. Make sure to re-level the bearing relative to the table upon re-assembly. Check to make sure the rubber washers between the bottom plate and the table are in good condition while you're putting it back together- you'll need them supple to take up the difference when you level the bottom bearing plate. Although a bit rough and crude, the original design wasn't too bad, but can be improved upon in these ways.
If this is "clear as mud" you can email me outside the forum.
I haven't contributed much during this thread as it has been concentrating mostly on fighting the original air arm
which I don't use for some of those same reasons. I do think the 'nolls are a neat platform that can be used as a
quite capable table, for pennies on the dollar compared to cost no object tables.
RFG