Max speed for Cast iron bearings

kenny14 · Oct 13, 2017

Hi..
Just for the fun of it, I have an old wood lathe that I would like to get up and running.
Only problem I have is that the 3/4" spindle runs in cast iron with provision for greasing.
It is fitted with a 3 step vee pulley, which would give it about 1040 rpm's on the slowest speed.
This sounds way too fast to me... your thoughts.
Ken.

partsproduction · Oct 13, 2017

Does sound too fast, especially for grease. Many fine metal lathes had steel spindles running in cast iron but running oil for lube. It's said they make excellent bearings IF the lube is constant.
I have an 85 year old Dalton lathe which runs the countershaft in cast iron bearings with ring oiler. These bearings function as if they were new, very little friction and no perceivable slop. The journals have oil reservoirs and the internal rings are constantly applying oil to the bearing surfaces. I'm impressed!
But they were designed to run no faster than 700 RPM or so.

billzweig · Oct 13, 2017

Plain bearings can run at high speeds - car engine main bearings are pain and the engine runs at 6000 rpm. The key is adequate lubrication and its supply. In machine tools with oil cups and grooves in the bearings the oil is delivered to the rotating surfaces providing an oil film between them; in fact the bearing and the shaft are not in contact, just when starting, stopping and under heavy loads. 3/4" spindle is rater small and can certainly run at 1000rpm and higher...with lubrication.

JST · Oct 13, 2017

Adequate oil, of course. Correct viscosity is also important. Faster generally means thinner oil. For a lathe, that runs at a variety of speeds, the oil has to be good for the lowest speeds, and then the high speed may be set by the limits of the oil, more than the bearing materials.

At higher speeds, the materials of the bearing never touch, at least theoretically. The only time they should touch is starting from a stop. The oil film is constantly being "sheared" because part of the oil sticks to the non-moving bearing, and part to the spindle, which is rotating. There is some place in the middle where the film is being sheared, and is turbulent. That heats the oil, more heating the thicker the oil is.

A car engine has pump fed oil, which is fed in after cooling in a sump. Because it is pressurized, it can be a bit thinner, plus it is cooled, so the bearings can be run faster.

muckalee · Oct 14, 2017

Did you proof read?

steve-l · Oct 14, 2017

The max speed of plain bearing is determined by the journal diameter and the lubrication provided, not the bearing material. Plain bearings are designed to be suspended in operation by the lubrication film and theoretically the journal should never touch the shell except at start up. In your instance, grease is fine at low speed, but not at the speeds you will be running at. At your 3/4" diameter, oil drip through a felt wick would be adequate until about 3000 RPM. Above that an oil pressure feed would need to be considered.

Other shell materials like Bronze, Aluminum and Babbitt provide additional attributes like conformability and imbed ability of particulate contamination in the oil.

enginebill · Oct 14, 2017

Many grinders had iron bearings and would run several thousand rpm with just oil cups for lubrication. I would not use grease though.

Mike C. · Oct 14, 2017

Sounds like somebody has replaced the original Gits cups or drip oilers with grease fittings. This is a common screw up by people who are lazy and don't understand machinery. The grease doesn't drip all over the place and you only have to grease it once every 50 years... I guess that is the thought.

As said above you need to have oilers on this spindle so the oil can run through and change itself. Grease in the close clearances of a good high speed plain bearing fit doesn't work well at all. My suggestion is to remove the spindle, clean up the bearings really well and chip all the dried grease out of the grooves in the shaft and/or bearings., find and fit a set of either gits cups with yarn wicks or (best) a set of drip oilers. Run a straight non-detergent 10 or 20wt mineral oil. Should be fine. Pay attention to the temperature of the bearings when running. If you can't lay your hand on the bearings after 10 minutes or so of running, you need to run thinner oil and/or slow it down.

kenny14 · Oct 14, 2017

Thank's guys .... will now re-evaluate the situation.
Ken.

Jeff_G · Oct 14, 2017

Tuckahoe has a Becker vertical mill ca. 1890 (see Cope page 19 figure 1). According to the book, the machine ran at up to 10,000 rpm on plain bearings, "a very high speed for that time". I'll take a look at the lubrication arrangement next time I'm there.

Spyderedge · Oct 14, 2017

Max speed for plain bearings is dependent on lubrication and the tolerances of everything. I am inclined to believe there are too many unknown variables to state a correct answer.

Automotive bearings are usually coated and have a constant flow of 40psi hot, filtered oil going through them. It's a very nice example of super low tech working incredibly well, but it can't really be compared to a wood lathe spindle with drip oilers and probably wood dust in the bearing.

Sent from my XT1053 using Tapatalk

CalG · Oct 14, 2017

Cast iron means nothing

The presence of "greasers" means nothing also. Oil guns often are fitted with Alemite couplings.

Think of a modern "automotive turbo charger", Cast iron bearing elements would not be a significant limitation.

Plane bearings pump lubrication into and out from the load surface.

swatkins · Oct 15, 2017

In the "old" days what was referred to as Grease is what we would call oil today.

Bridgeport mills have zerk fittings on the tables and most of the ones I've looked to buy have had the passages clogged with thick grease instead of the proper oil.

This might be the case with your old lathe.

Mike C. · Oct 15, 2017

"Plane bearings pump lubrication into and out from the load surface."

Indeed and this is the reason grease can't be used. It doesn't pump, it just starts recycling. With total loss oiling, as in a drip oiler or wick oiler, the oil is drawn into the bearing and runs out at a very slow rate. That keeps fresh clean oil going into the bearings. Pack grease in there and the heat directly in the bearing will turn to liquid and provide some lubrication, but the grease that runs out never gets hot enough to remain liquid and run out of the bearing, and incoming grease also never gets hot enough to become liquid and run into the bearing. Result is a stagnant black muck that becomes powdered metal and solidified waxes out of the grease. Grease and high speed plain bearings just don't agree.

That changing is also why the plain bearings can live in the environment of a wood lathe without gumming up woth wood dust. The oil flushes itself out, so the dust gets flushed out, too.

Danny VanVoorn · Oct 15, 2017

A common misconception is thinking just because a Zerk fitting is there that it's for grease and not oil? On machines especially made in Europe were sent from the factory with Zerks for all lubrication points for various grades of machine oil and a lot suffered because that mistake was made.
Dan

kenny14 · Oct 16, 2017

What clearance would be considered OK on my 3/4" shaft ?.. they are the split type adjusted by means of a 1/4" screw.
Although the journals and bores look fine, I am hesitant to take up adjustment past the nip up stage.
Ken.

billzweig · Oct 18, 2017

kenny14 said:
What clearance would be considered OK on my 3/4" shaft ?.. they are the split type adjusted by means of a 1/4" screw.
Although the journals and bores look fine, I am hesitant to take up adjustment past the nip up stage.
Ken.

As it was indicted by many above, proper fit of the shaft and bearing is essential for the correct operation. The common way for adjustable bushings are split in half bushings with shims for adjusting the clearance and various taper arrangements either the bearing and shaft being tapered or slotted, inside cylindrical bushing, and conical adjusting sleeve on the outside. As for the clearance between the bearing and the shaft it is seldom actually measured, just adjusted by feel, the "clearance" being (for proper operation) in microns (1/25s of thousand). Too little gap and the oil will not penetrate(and the shaft probably binding at spots), too much and the oil cannot form the hydrodynamic pressure and could quickly leak out altogether. Of course to achieve this type of fit, both the bearing and the shaft need to be of close tolerances when it comes to roundness etc.
The type of adjustment with a single split and screw can seldom meet those demands. The best you can do (after cleaning and lubricating with fresh oil) is to tighten the screw slowly until shaft starts to bind and the release the screw VERY slowly until the shaft is rotating freely.

Search

Largest Manufacturing Technology Community on the Web

Search

Max speed for Cast iron bearings

kenny14

Plastic

partsproduction

Titanium

billzweig

Stainless

JST

Diamond

muckalee

Cast Iron

steve-l

Titanium

enginebill

Stainless

Mike C.

Diamond

kenny14

Plastic

Jeff_G

Hot Rolled

Spyderedge

Titanium

CalG

Diamond

swatkins

Titanium

Mike C.

Diamond

Danny VanVoorn

Titanium

kenny14

Plastic

billzweig

Stainless

Similar threads