Plain bearing sapeed limitation

Machines with anti-friction bearings can run faster than the old plain bearings, so it is said.

But, why? Engines running at 7,000RPM and turbochargers going much faster use plain bearings, albeit with pressure lubrication.

Why could not an old lathe be run at carbide speeds, if you ran enough oil through it to keep the bearing temperature reasonable (might be messy!)?

You want to run an old engine lathe at 7000 rpm?

Hit the button and stand back!..........wayyyy back! Haha

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You need to think to that those (high speed) lathes also have chiller units to keep the bearings cool. And there is a difference between regular and high speed bearings. Not sure exactly what, (I'm not a rocket scientist)

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As the others have said you can You will probably fail if you do it. You will create a lot of heat. You should look it up in the Machinery Handbook where it has charts on plain bearings and clearance. It all depends on the diameter of the shaft and bearing size or contact area. I would suspect you will have to have the clearance at least .010" as it will get hot and expand. So you won't be able to use it at lower RPM's. Many of the old machines needed a warm up period so the clearance became right. Also we used to start the motor and shut it down and on again to ramp up the machine to speed otherwise the power draw blew the fuses.

I have seen lathe owners that have ball bearing head-stocks that have ruined the bearings by changing the motor RPM. If I were you, save your self a major accident and buy a lathe made to run 7000 RPM. Remember there are sorts of other bearings and mechanics involved in the machine that need to turn at the higher RPM. Very Dangerous if you do it. As the other guy said..."STAND BACK"....lol

Many old plane grinder spindles ran at 3 and even 6k..

Discipline, technique and design would require a guaranteed oil supply, a slow roll start, a higher electric (power source) need and a warm up period.. But would/may offer better surface finish and size holding and likely longer life..IMHO.

A plane bearing will sag out the oil so running up to speed at the get-go will/may harm the bearing. A machine that may need 1/2 hour (perhaps more) to get to final tempature will lose that time at every cold start. Don't remember the increased power need but for a shop full of machines it can be a lot. I may find some notes on that but might be 20 to 50% so one might need to go from a 1 hp to a 1.5 hp motor , or 5 to 7hp (?)..

When you get to about and above 3000 rpm a spindle can act like a giroscope and tend to try to lean, travel or twist in a certain direction...so if not properly balance can lean out the oil on one side..

Some of the heavy chuck big old lathes should not be considered with everything not balanced for such speeds.
Here find a paper on the same (it misses a few important points)
Plain Bearings Outperform Rolling-Element Bearings | Machine Design

Simple comparison is a scraped oil way machine and a ball(or roller) travel way machine. The ball and roller travels much easier but not near as smooth as the oil way machine and the oil way machine may need a warm-up..

Engines can run at 9k RPMs (in some cases) because of forced lubrication and proper clearances. That's the "secret".

Research hydrodymanic bearings. They're also used in conventional hard drives.

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Once saw a guy trying to blow the engine of an old Packard straight 8, it was about a 1952 or so(?). Flat out it must have been running 5K perhaps better..he got tired of holding the petal down and gave up before it gave in...Don't ask me why he would do such ....he just said I want to blow it up.
Don't think it had super oil pressure but it did have oil..

likely it took us 10 minuets to walk down the street and perhaps another 10 minuets waiting for it to blow a rod. so it may have run that way for a half hour..

Wow Packard plane bearing 12 1932-1939 Packard Twelve | HowStuffWorks

Thanks for the thoughtful replies..and the others.

I'm not planning to run my old New Haven at 7K RPM.

But there is nothing very different between the plain bearings in an auto engine capable of sustained running at 3,000RPM, and those in the New Haven, the materials are similar , so are the clearances. The engine does benefit from warmup before seeing heavy loads, but does not need hours of it.

I am a little familiar with plain bearing calculations, involving speed, temperature, load, oil viscosity, clearance. I'm just questioning the old-wisdom that plain-bearing lathes have to run slow, under 1,000RPM, asking if anyone knows WHY a plain bearing, such as a lathe spindle, in good condition, with clearance of one to a few thousandths, WITH ample, maybe forced lubrication (not the original wick or oil-ring), cannot run at, say, 2,000RPM. Michiganbuck mentioned grinder spindles...

Call it a thought-experiment. Call me an idiot.

Still a big old girl is not made for small aluminum parts.
New Haven Manufacturing Co. - 1912 Ad-New Haven Manufacturing Co., 18 inch Engine Lathe | VintageMachinery.org

We had high precision machine bearing spindles that were rated for 900 RPM (yes nine hundred).. its all about how they are set up and heat tested for heat rise at a certain RPM.. You don't want to wreck a spindle running it a way over spec..
Guess I might go 25% higher than stated on a broke in spindle using the best oil and being careful.

likely a well used machine would have wear clearance to allow going higher but to lose a spindle would make it not worth saving a little time on a part.