Deassembling air float rotary table. . .tips or precautions ?

12" diameter CMM Rotary table is drawing high amps and frequently blowing fuses. It is an air floatation table and there is air to the machine.

It is an M&M Precision model 3000 , I'm guessing 18-20 years old.

Works well except for this

David Lawrence

I assume this is a motor-driven air-bearing table; is it connected in any way to the CMM control and power circuitry? It isn't real clear what the setup is. In any case, it may be that the air supply to the rotary table has been bringing gunk into the air bearing assembly, either in a recent slug, or little by little over time. The typical clearances for these air bearings are in the neighborhood of < 1 micron, so disaassembly and cleaning can be a dicey proposition. I had the above problem with a Precitech/Pneumo Precision 8" rotary table, and it went back to Precitech for cleaning. Cost me $500, as I recall, but the air bearing is about $12K new, so not so bad. This kind of problem could easily cause the symptom you see.
If you do choose to try it yourself, set up for surgical cleanliness at the point of reassembly. And ideally you have a way to check the air bearing accuracy when you're done. I use a grade 10 ball bearing, about 1.5" for sanity checks on this kind of equipment. The factory would typically use a 2 microinch gage ball for calibrating.

The table rotation is directly controlled by the CMM , Its part of it , To check a helical gear there is simultanous motion of the rotary axis and several of the linear axises . We have heard of running isopropal alcohol into the airline , are getting ready to try this .

How do you use the ball bearing in checking this type of table?

David Lawrence

David --

M & M Precision has changed hands a couple of times since I last dealt with them, but in my experience they've provided exceptional telephone support. Unless you've already run into the proverbial brick wall with them, I think you'd be smart to sink a bit of time and money into a telephone call. The telephone number I have for them is (937) 859-8273.

John

If the bearing turns freely the problem is likely not with the bearing. The clearance is more like 5 micrometers, not 1 but any real metal to metal contact will really stick the spindle and it definitely will not spin freely. If it is belt driven you can take the belt off and the spindle should spin for many minutes after just one good hand spin. If it spins like that the problem is definitely not the spindle. If you have a good air filter and dry air you shouldn't have a problem with the bearing. The alcohol may or may not flush debris out. Use alcohol with no water in it or as little as possible if you try that. Oil, coolant, water wicked back into the clearance when the air supply happens to stop will stick an air bearing. I like the suggestion of calling the manufacturer first. Easy to fix if you know what you are doing and easy to ruin if you don't.