Filmatic Bearing repairs

[madman]

Im thinking (OH OH) of doing a filmatic bearing repair on friends enterless grinder. Basically it is just the reg Wheel side (giant rubber roller wheel moves slowly) i thought turn and grind ashaft the same diameter as the bearing housing, Then lightly oil the shaft moglice the crap out of the sheell bearing faces after degreasing them. Then clamp tightly to the finish ground shaft and then perhaps scrape blue scrape ect. until proper amount cleanup, perhaps a bit opener at the oil intake side or end?? Any thoughts on this you canny bunch of machinists?/ i think it may work out well?? thanx Mike

[lazlo]

From your other thread Madman:

I had to Google "Filmatic bearing" and the first hit is this thread Apparently a fluid-film (hydrostatic) bearing? That sounds way out of the realm of repair in a home shop.

Here's a cool diagram of Cincinnati's Filmatic bearing:

http://books.google.com/books?id=QrQ...um=6&ct=result

[mochinist]

This is just my opinion but if I had to ask how to repair a machine other than my own, I would probably not do it. I guess if you're working for free and your friend doesn't care if you eff-up his machine then go for it, otherwise pass. There is exceptions of course, like if you have done similar repairs on other machines, but it sounds like you have never done anything like this before.

[pcarpenter]

Along the lines of what Mochinist posted....

if the repair could involve only the moglice "rework" of the existing worn out plain bearing (something that is by definition trash since its now wallowed out), I would be more apt to say "go for it, you have little to loose". Since it sounds like the shaft is out of round or something, then you are now talking about cutting on a part that could be big dollars to replace. On the other hand, it sounds like you may be set up to do precision grinding so it may not be that unreasonable. Edit-- nevermind....I see you are talking about turning and grinding a dummy shaft.

All oil-lubricated "plain bearings" are "hydrodynamic bearings" in that the real bearing surface is supposed to be the film of oil involved. If a shaft spent much time touching an unlubricated babbit bearing, for example, you would have tin galled onto the shaft. Tin seems to be rather "sticky" stuff. They line the bores of starter solenoids and I have seen cases of sticky solenoids fixed only by wiping off the rubbed-off tin off the slug.

In any case, the key will be getting the fits right such that the film is kept constant given the original oiling system. The other issue I would think, would be preserving alignment????

Paul

[tdmidget]

As has been said it is basically a pressure fed plain bearing. Alignment wise is not a real big problem because although you might not match up to the machine's graduations a centerless has more adjustments than you can shake a stick at. I'd be more worried about longterm compatibility of the repair medium with the oil. Also the speed of the regulating wheel may be low but it is heavily loaded.

[lazlo]

As has been said it is basically a pressure fed plain bearing.

A plain bearing is a hydrodynamic bearing. It relies on the rotation of the two halves to create an oil wedge.

A hydrostatic bearing, like the Cincinnati Filmatic bearing, or an air bearing, uses a positive pressure supply that maintains clearance between the rotating elements. Like an air bearing, hydrostatic spindles have very high stiffness and long bearing life, and are used in high-end machining and finishing.

So Madman is basically trying to repair an air bearing (that uses oil instead of air for the fluid), not a plain bearing.

[kf2qd]

It would seem that the fit & finish of the shaft and bore are important. It is probably a bit tighter tolerance work than the home machinist is used to. It shouldn't be all that difficult. The backer wheel is probably trued up by grinding it in place. As long as the clearances are correct it will work. SOunds like a fun project.

[Rustybolt]

There is adjustment for those bearings. Everybody is right. They ride on a film of pressurized oil. If he has oil pressure,unless the line to the bearing is blocked, they should be alright. If I remember correctly oill pressure should be around 12 psi. Remember to change the filter. There were factories where the centerless grinders ran 24/7 for months on end. I even ran into one that had water in the oil. A lot of it. The Cinncinatee rep asked if it was rusty water. Nope. Just change the oil then and keep running it.

Why does he think the bearing needs to be rebuilt?

[lazlo]

They ride on a film of pressurized oil. If he has oil pressure,unless the line to the bearing is blocked, they should be alright.

Right, like an air bearing, if you provide enough fluid pressure to maintain the proper float, it should never wear, and it also has the same huge benefit that conventional air bearings do that the positive pressure displacement flushes out any grinding grit that may have gotten in between the bearing halves.

But from his description, it sounds like someone crashed the bearing.

If you can find the Cincinnati Filmatic patent, it probably describes the clearances necessary -- I'd imagine, like an air bearing, it's really tight...

By the way, I seem to recall that large ships use hydrostatic bearings in the props because it dramatically reduces vibration over plain bearings, and retains it's float at very low RPM (due to the positive pressure displacement).

[madman]

My Friend had a ??PRO?? come in and charge an ARM AND A PIT to adjust the filmatic bearings in his Grinder and it didnt really work any better, At best now its a roughing machine??? Well i dont think i could screw it up much worse and i think my idea has some merit. Also the reg wheel does NOT turn very fast? I was even thinking (dangerous act) of a pair of pillow block bearings to mount the spindle in?? ) We shall see what happens. I love doing things that people tell me i shouldnt LOL. It seems to work out USUALLY yet i have done some dumb ass stuff at times. Its the best way to learn i guess. Remember the Motto THOSE WHO DARE WIN???