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View Full Version : Knurling's bad for bearings - Fact or Fiction?



KiddZimaHater
08-31-2011, 08:07 PM
I wish this were covered on Snopes.:)
Is knurling with the old style "side-load" knurling tool REALLY as hard on bearings as people make it out to be?
Has there ever been an actual instance where bearings have failed or gone bad due to side-load knurling?
I ask, because it seems that on every knurling thread, or knurling tool sales add, or Ebay, or where-ever... everyone praises the almighty scissor-style knurling tool, and proclaims death & destruction to your lathe if you continue sinning and using the "Evil" side-load tool.
So what's the poop?
I can understand a lathe wearing out if it does nothing BUT knurling, all day, everyday, year after year.
But the fear-mongering seems a bit much.
Just sayin'

Mcgyver
08-31-2011, 08:16 PM
take a pass, get the electron microscope out and have a look

Bearings eventually where out, whether you are drastically hastening that depends if you're doing a coarse knurl in prehardened 4140 in a single pass :eek: or mushy aluminum, if the lathe's a Pacemaker or asian mini.
If you really load them and cause very minor brinelling, you've shortened their life, who knows if its very much and when/if you'll notice.

Bottom line though is there's no really easy answer or way check. Given how fundamental they are to accuracy as well as difficult and expensive to replace, I think most guys, me included, sit in the better safe that sorry camp.....unless the lathe is rather heavy duty

Also, be somewhat concerned about over straining the cross feed and nut

Scottike
08-31-2011, 08:28 PM
I think it has to depend on the lathe, the operator, the material, and how often it's done.
As you said, in a production setting I could see it taking away from the life of the bearings, even that could be debatable, but at least seems reasonable on the surface.
I think the bottom line would be the axiel?? (side load) thrust rating for the bearings and most lathes have a pretty substantional bearing rating. but I'm pretty sure that someone could exceed that if they got carried away. (what's gonna give first, the 1 inch stock your knurling, the knurler, or the bearings supporting the 2"+ od spindle?)

edit: Or as Mcgyver said - "the cross feed and nut"

Forrest Addy
08-31-2011, 08:54 PM
Time for a sage and worldly old fart response and a Sophoclean question: Nope. What fool told you that?

platypus2020
08-31-2011, 09:00 PM
I was starting up some new industrial boilers for a company that was a sub-contractor to Lockheed, the boiler room was right next to one of the machine shops. They had bought a new big buck lathe, and this question came up, they had 3 stress engineers, with all kinds of test equipment for almost a week, running test on bump or side type knurler vs the scissor type. Their findings were it took exactly the same amount of side force on the spindle to raise the exact same size knurl, in the same type material, regardless of the type of knurler used.


jack

lazlo
08-31-2011, 09:07 PM
Depends on whether you have HSS or carbide bearings :p

Scottike
08-31-2011, 09:14 PM
I've found that the rubber bearings are are quiter and more forgiving

Grind Hard
08-31-2011, 09:20 PM
Best way to avoid wearing out your tools.... don't use them at all.

Seriously. Tools are for using and making things. That's why we have them.

No point in owning a lathe if you are afraid of it "wearing out" or some silly nonsense like that!!

Tanto
08-31-2011, 09:33 PM
Have you used one? If so you'd feel just how hard they are not just on the bearings, but pretty much the whole machine. To me it's a bit like owning a family sedan and always revving it to the redline, do it once and there shouldn't be a problem, but strain the engine like that constantly and that's when you'll start to see issues arrise.

Evan
08-31-2011, 10:49 PM
It doesn't have any effect on well lubricated plain (plane) bearings. Plane bearings are the heavy lifters of the bearing world.

Carld
08-31-2011, 11:01 PM
How ham fisted are you when you knurl? If you try to knurl in one pass your over doing it. Knurling SS or hard steel takes a lot of pressure. A small lathe may not take knurling so well. A 14"x40" gear headstock with good bearings can take the load.

What few times you will knurl will not hurt your lathe.

Black_Moons
08-31-2011, 11:15 PM
I don't see how a sissor knurl could come even close to the pressure required for a press knurl to work.

a sissor knurl asorbs all the 'side' force itself, all thats left is carriage feed force.

wooleybooger
09-01-2011, 12:53 AM
Im not so worried about the bearings as much as I am about the crossfeed nut.

Tanto
09-01-2011, 01:20 AM
Im not so worried about the bearings as much as I am about the crossfeed nut.

That's my 2 cents worth too. It's not as much the spindle bearings but the rest of the machine that takes a hammering when knurling.

boslab
09-01-2011, 02:24 AM
It doesn't have any effect on well lubricated plain (plane) bearings. Plane bearings are the heavy lifters of the bearing world.
tis true plain shells are used on rolling mills [morgoil bearings] you cant get more extrime than a reversing roughing mill fitted with a couple of 11000A motors mangling slab steel!
i wouldent worry about your bearings as much as the cross feed as has been mentioned, it has affected mine as the backlash is getting worse, to the point i dont do much parting as a rule as the old dear is prone to snaching of late, a refit is on the cards! new harrison nut and screw wont be cheap so single pointing may be forced on me and my last effort on a square thread was abysmal!lol
regards
mark

philbur
09-01-2011, 04:07 AM
Why not, intuition says yes?

Phil:)


Time for a sage and worldly old fart response and a Sophoclean question: Nope. What fool told you that?

DATo
09-01-2011, 05:58 AM
I don't see how a sissor knurl could come even close to the pressure required for a press knurl to work.

a sissor knurl asorbs all the 'side' force itself, all thats left is carriage feed force.

Knurling on engine lathes has been around for a long time so my guess is that the pressures imposed by knurling are factored in when the bearing design for a lathe is made. In my entire career I have never worked at a place which had to replace the headstock bearings on a lathe and everywhere I worked knurling was done at one time or another to greater and lesser degrees, so I doubt that it is a serious issue. Two points: one, I have always been fortunate to work with quality lathes; two, Black_Moons point is well taken - if you want to play it safe use a sissors knurl.

DATo
09-01-2011, 06:04 AM
[Originally Posted by wooleybooger
Im not so worried about the bearings as much as I am about the crossfeed nut.]

That's my 2 cents worth too. It's not as much the spindle bearings but the rest of the machine that takes a hammering when knurling.

Both nut AND screw, but either or both can usually be easily replaced. I agree with those who say the machine is meant to be used so go ahead and use it with the understanding that maintenance is just part of the game. This is another good reason to purchase a machine from a company which offers good support. I have had very good luck (so far) with Jet which is the brand of lathe and mill I bought new.

I think the odds of ruining a lathe by knurling are marginal at best.

jugs
09-01-2011, 06:23 AM
I was starting up some new industrial boilers for a company that was a sub-contractor to Lockheed, the boiler room was right next to one of the machine shops. They had bought a new big buck lathe, and this question came up, they had 3 stress engineers, with all kinds of test equipment for almost a week, running test on bump or side type knurler vs the scissor type. Their findings were it took exactly the same amount of side force on the spindle to raise the exact same size knurl, in the same type material, regardless of the type of knurler used.


jack

Don't know what they were measuring, but it wasn't side load (were they engineers suffering from stress ??)

The scissor type give practically no side load apart from the thrust toward the chuck if you power feed.
The bump knurl puts large side loads on bearings & cross screw & can also strain the chuck :eek: . I only use bump style on alu.

Davidhcnc
09-01-2011, 06:30 AM
Do it like this and you will have no trouble

My knurling tool

http://homepage.ntlworld.com/david.hull35/CNC/knurl%20001.jpg

Touch on to the work like this and zero the dial.

http://homepage.ntlworld.com/david.hull35/CNC/knurl%20002.jpg

Start up and fed in until a good pattern is achieved.

http://homepage.ntlworld.com/david.hull35/CNC/knurl%20003.jpg

Read the dial. This is 1.8mm. Now we know where we are going. Notice the dodgy knurling on the dial!

http://homepage.ntlworld.com/david.hull35/CNC/knurl%20004.jpg

....more

Davidhcnc
09-01-2011, 06:31 AM
........

Approach the knurling as screwcutting, lets say 5 passes to arrive at the final depth. First pass, withdraw and reposition for the next pass..you know the drill.
The knurls are registered each pass by the prestarted band.

After first pass

http://homepage.ntlworld.com/david.hull35/CNC/knurl%20006.jpg

Completed.

http://homepage.ntlworld.com/david.hull35/CNC/knurl%20008.jpg

Mystery steel 1" dia, speed maybe 300rpm and feed whatever you cut at, coolant, if you have the luxury or oil.

Ian B
09-01-2011, 09:35 AM
Bad for the headstock bearings? How about the 'bearings' in the knurling tool itself - just a hardened steel pin running in hardened steel knurls, lubricated by a random mix of oil, cutting fluid and fine swarf. They seem to last well enough.

Knurling probably puts the same radial loading on the headstock as heavy drilling puts axial load on. Wouldn't worry about it.

Ian

J Tiers
09-01-2011, 09:47 AM
Well, the Logan I have has ball bearings.... a double-row angular contact nose bearing.

The rated-life RUNNING load for that bearing is around 8000 lb. 4 tons.

The static load is higher.

Now, nobody would want "only" rated life on a lathe spindle bearing, but you need to look at the rest of the system.

I suspect there is no way that the carriage/crosslide & screw/compound & screw/toolpost system is capable of applying anything near 8000 lb pressure. * And I don't think the chuck could take it, nor the spindle support it without considerable deflection, if not exceeding the elastic limit.

Talk of "brinnelling" the bearings or other damage by knurling does not sound reasonable.

* the leadscrew is 10 tpi, and the handle has a radius of about an inch, so a circumference of movement of 6 inches or so. The 8000 lb moved 0.1" would equate to 6" handle travel, a 60:1 advantage with no friction included. Therefore the turning force would need to be around 100- 130 lb.... very unlikely, even if the structure could take the 8000 lb force.

What you would consider an unreasonable turnng force on the crosslide is likely to be only 600 lb force on the cutter at max.

Lew Hartswick
09-01-2011, 09:47 AM
<Also, be somewhat concerned about over straining the cross feed and nut
edit: Or as Mcgyver said - "the cross feed and nut"
Im not so worried about the bearings as much as I am about the crossfeed nut.
That's my 2 cents worth too. It's not as much the spindle bearings but the rest of the machine that takes a hammering when knurling.
i wouldent worry about your bearings as much as the cross feed as has been mentioned,
Both nut AND screw, but either or both can usually be easily replaced.
>

I guess I'm on the side of all those previous posts. :-)
...lew...

baldysm
09-01-2011, 10:55 AM
In HSM a few months ago, there was a series of articles on a cut knurler.

I'm working on it, have not finished it yet. It would seem to be much better for the lathe, both bearings and cross slide nut than a knurler that works by displacement.

About the only disadvantage to it I see is that you cant use it to enlarge a shaft a wee bit to better fit a hole.

Depending on the material, you might work harden the material when making multiple passes.

On a side note, I was doing a small production job that was knurling a short section of 2" dia stock. Sometimes I got a nice diamond pattern, sometimes I got a double cut. Never did figure out why the difference, same technique, same setup, same knurl tool, same rod of stock used, etc. but yielded inconsistent results.

justanengineer
09-01-2011, 12:03 PM
I see the CNCs at work running push-type knurlers all the time without issue, and they arent half as careful to take multiple passes as I am. I forget what the bearings in my lathe are rated to, but I also know theyre rated significantly more (factors higher) than the forces generated by knurling. When you consider the forces imparted by parting and other cutting operations, Im not too worried about knurling.

Regarding the cross feed screw and nut, who cares? The great part about a lathe is that even one with a ridiculous amount of backlash can easily create its own replacement crossfeed screw and nut.

philbur
09-01-2011, 12:15 PM
You have to also consider the applied force as a moment which will increase the bearing load some what, maybe worst case x 2. But yes the numbers would indicate that for a "normally" constructed lathe it will be difficult to overload the spindle bearing.

Things might be different for a plain bearing. When knurling the spindle speed will be low and the hydro-dynamic effect of the oil film low to none existent. Possibly you would then get metal to metal contact and rapid wear.

Phil:)



* the leadscrew is 10 tpi, and the handle has a radius of about an inch, so a circumference of movement of 6 inches or so. The 8000 lb moved 0.1" would equate to 6" handle travel, a 60:1 advantage with no friction included. Therefore the turning force would need to be around 100- 130 lb.... very unlikely, even if the structure could take the 8000 lb force.

What you would consider an unreasonable turnng force on the crosslide is likely to be only 600 lb force on the cutter at max.

aboard_epsilon
09-01-2011, 12:21 PM
seems the thing to do then :-

is to oil your cross slide screw and your head bearings just before you do any knurling

all the best.markj

Forrest Addy
09-01-2011, 12:31 PM
First of all the assertion that knurling might be "bad" for "bearings" (headstock or spindle) is plain ridiculous. OTH it's stimulated vigorous debate. Assertion and counter-assertion supported by "a guy tole me" is hardly fact based, plausible, or evidentiary. Debate leading to analysis using the available facts may lead to a rational conclusion.

I like JR's approach: look at the numbers. Somewhere for your lathe is an entry in the spec sheet or parts list that will lead you to a load rating for the front spindle bearing. Live centers may be more difficult but you can estimate by finding a cross section, eyeballing the bearings, and digging through catalogs. Somewhere there's comprable bearing(s) that will enable you to deduce a load rating for your live center. While your load rating data may be in part inferential it will give you a place to start.

Next is how much thrust does it take to feed in the knurling tool? You have a cross-feed screw. You can look at it and determine the dia and pitch. Mine is 1 1/8 -5 Acme about 4 degrees helix angle. The handwheel is about 5" in dia. At a WAG it takes about 40 in lb to crank a 1/4" wide face knurling tool in from the solid. Working the math that's very roughly 1400 lb.

My live center is the weakest link particularly the center hole. A 5/16 dia center prep has about 0.1 width of bearing. Doing the math using 1/3 the net circumference works out to unit loading roughly equal tp the yield point of mild steel, that is, a vigorous thrust to infeed a knurl may cold upset a typical center hole: the center may loosen up. I've experienced this but I never before put numbers to it. 1400 lb thrust to sink in a 1/4 knurl might be a ball park figure.

Look at your bearings and your estimate of their load rating. Apply the 1400 lb figure. Do the math. Now if you don't know for absolute certain, you have a good first approximation. Knurling is "bad" for bearings? Yeah, where the live center bears on the conical wall of the combination center-drilled prep in the end of the work. Not the bearing you had in mind was it?

Even rough analysis like this is light years ahead of "a guy tole me".

With a little practice you can run analyses like this in your head while staring skepticaly at your informant. Have "bull$hit" "show me" and "OK" ready to your lips. Make the appropiate utterance when your rough analysis is complete. Soon liars and purveyors of unsupportable legend will be careful to screen casual remarks before addressing them to you.

davidwdyer
09-01-2011, 12:35 PM
The best way to never wear out tools is never use them.

ANY use of any tool produces some kind of wear.

lazlo
09-01-2011, 12:51 PM
OTH it's stimulated vigorous debate. Assertion and counter-assertion supported by "a guy tole me" is hardly fact based, plausible, or evidentiary.

We never, ever, do that. :rolleyes: :D

philbur
09-01-2011, 02:27 PM
I tihink he is refering to fact based, plausible, and evidentiary posts similar to the following:

"Time for a sage and worldly old fart response and a Sophoclean question: Nope. What fool told you that?"
Phil:)



We never, ever, do that. :rolleyes: :D

Evan
09-01-2011, 02:50 PM
Things might be different for a plain bearing. When knurling the spindle speed will be low and the hydro-dynamic effect of the oil film low to none existent. Possibly you would then get metal to metal contact and rapid wear.


While that sounds reasonable the opposite is true. Those are precisely the conditions where plain bearings excel. That's why they are use in the wheel bearings for machines such as container cranes for loading ships.

Also, I do a fair amount of knurling on my SB and the spindle on it looked nearly new when I overhauled the headstock recently.

added: In fact, it is very low speeds that are the most destructive to rolling element bearings.

philbur
09-01-2011, 04:01 PM
But is that with forced lubrication or gravity feed. Also such a wheel bearing is designed for a relatively narrow rpm range, much different from the rpm range of a plain bearing in a lathe spindle.

I think it is a mistake to use one application as justification for use in another without understanding the differences.

Phil:)


That's why they are use in the wheel bearings for machines such as container cranes for loading ships.

Evan
09-01-2011, 04:30 PM
I think it is a mistake to use one application as justification for use in another without understanding the differences.

It isn't a mistake. Plain bearings are best suited to heavy loads at low rpm with or without forced lubrication. They don't just rely on the lubricating film to prevent wear. Plain bearings are constructed of materials that have little affinity for each other and are to a large degree "self lubricating". Also, it is impossible to "squeeze" out all traces of lubricant in a properly lubricated plain bearing regardless of load or rpm.

The fact remains that it is precisely the conditions presented by conventional knurling where plain bearings excel.

sch
09-01-2011, 04:40 PM
Metal scrap box at the JC I futzed at a while back had 3-4 acme
thread 1/2" screws with really bolluxed up sections about 3"
long where the acme looked almost like 60D threading. Asked
the instructor what was up and he indicated they were take offs
from the 9-10" and 12" lathes (all Taiwan made South Bends)
worn out from the stress of knurling, which all the students
do on several projects in their first year. They were the cross
slide drive screws.

rohart
09-01-2011, 05:32 PM
A rougher analysis than Forest's, applied to the question of forced lubrication of a plain bearing goes like this.

My bike's oil pressure = 40 lb/sq in.

My bike's big end bearing = 1 1/2 sq in.

Pressure on the firing stroke from the piston = a great deal more than 60 lb.

Conclusion = pressure is not enough to hold the two surfaces apart.

It's the relative rotation of the two surfaces with an oil film than keeps them apart. The pressure is used to fill the gap whenever the unloaded gap coincides with the oil hole in the crank. The rotation will see to the oil film being spread around the bearing.

jep24601
09-01-2011, 05:51 PM
I don't see how a sissor knurl could come even close to the pressure required for a press knurl to work.

a sissor knurl asorbs all the 'side' force itself, all thats left is carriage feed force.
The scissor knurl I use tightens with a nut and bolt directly on the scissor. No intermediate loadings. Much nicer to use than a straight push knurl. Easily tightens to exert sufficient pressure. I wouldn't recommend a push knurl to guys with small machines.

Tanto
09-01-2011, 06:06 PM
Bad for the headstock bearings? How about the 'bearings' in the knurling tool itself - just a hardened steel pin running in hardened steel knurls, lubricated by a random mix of oil, cutting fluid and fine swarf. They seem to last well enough.

Ian

Ian OT, but I have a number of knurling tools and my cheap scissor style is showing significant wear on the pins. I suspect that is more to do with the quality of that particular tool than anything, however it's getting to the point that they're going to need to be remade quite soon.

John Stevenson
09-01-2011, 06:59 PM
new harrison nut and screw wont be cheap so single pointing may be forced on me and my last effort on a square thread was abysmal!lol
regards
mark

Mark, What size is it ?
I recently bought all the feed screw taps from Myfords and there are loads of different sizes

J Tiers
09-01-2011, 11:12 PM
A rougher analysis than Forest's, applied to the question of forced lubrication of a plain bearing goes like this.

My bike's oil pressure = 40 lb/sq in.

My bike's big end bearing = 1 1/2 sq in.

Pressure on the firing stroke from the piston = a great deal more than 60 lb.

Conclusion = pressure is not enough to hold the two surfaces apart.

It's the relative rotation of the two surfaces with an oil film than keeps them apart. The pressure is used to fill the gap whenever the unloaded gap coincides with the oil hole in the crank. The rotation will see to the oil film being spread around the bearing.

Actually, it is the resistance to flow..... the high pressure is "on" for a short time, then off again and forced lube can fill it up again.... During the "on" time, the oil cannot all be forced out, so it stays in place.

With a plain bearing, it IS possible to generally force out most of the lube.... especially oil. Grease tends to be used for slow plain bearings.

I'd like to see Evan's justification of his unsupported statement.

I don't necessarily think he is wrong, I just want to see the reasoning behind it.

Evan
09-01-2011, 11:29 PM
What unsupported statement?

J Tiers
09-01-2011, 11:56 PM
Chill.....

No attacks here....

I wondered why the plain bearing in general was especially good for low speed...... and ball/roller especially bad.

Yeah, babbit is somewhat low friction, but metal-to-metal it will wear down fairly fast at high pressure...... don't ask me how I know this.......

But not all plain bearings are babbitt, there are other kinda soft materials used, and some are hardened against hardened also.

Evan
09-02-2011, 12:20 AM
Here are plane bearings that are intended to run dry metal on metal.

http://bearing.firstbronze.com/viewitems/powdered-metal-bearings-and-thrust-washers/dri-plane-sleeve-plain-bearings.

The advantage of plane bearings is area. Not point or line contact but area contact, dry or lubricated. It is the far smaller contact area that kills rotating element bearings and the slower they run the worse it is. Also, the static load rating on ball bearings is much less than the running rating. Static load ratings are usually about half the running rating.

J Tiers
09-02-2011, 12:38 AM
A plain bearing MUST have a semi-line contact if dry...... otherwise it was a shrink-fit and not much good for a bearing.

The shaft must be smaller in order to turn, and if so, it will contact in a line, aside from deformation of parts.

A ball or roller also deforms the race and ball so as not to have a line or point contact.

While THAT bearing is not intended to have oil, it does have a solid lube. but most are not like that.

it seems to be fairly well known that the oil is substantially pressed out after standing, and also that heavy loading (which presses out lube) causes wear.

I would suspect a DRY ball bearing operating within its limits will last longer than a DRY journal bearing using babbit. Ditto for bearings which have had oil, but have had it drained out. The ball bearing has less friction when dry than the babbit, usually.

I thought maybe you had a reference dealing with it, perhaps with experimental data.

No sweat.

Evan
09-02-2011, 12:55 AM
Look up the PV curves for plane bearings and compare them to the load rating for rolling element bearings of similar size. There are plenty of references available.

Based on the "everything is made of rubber" principle a dry plane bearing will not be just a line contact, far from it. It will have a relatively large contact patch since the two curves are nearly the same.

J Tiers
09-02-2011, 01:22 AM
Based on the "everything is made of rubber" principle a dry plane bearing will not be just a line contact, far from it. It will have a relatively large contact patch since the two curves are nearly the same.


Also true of ball bearings, which develop a larger contact patch under pressure, and of roller bearings, which do the same....

The difference between them and a journal bearing is that they are not MOVING those surfaces against one another at the same speed as the rotation.

There will be some "scrubbing", but that is far less than the out-and-out 1:1 rubbing of the shaft on the dry bearing material. (in the case of dry or thoroughly drained bearing).

Developed heat should be widely different...... which is not to say that dry ball bearings are good..... they fail, they just take longer than a journal bearing is likely to take to start melting or material transfer from the bronze or babbitt. longer in total turns at any given speed.

In any case, we have made a side trip long enough..... this has little to do with knurling.... we are just arguing out cases about the bearings... a known hot-button around here.

What you think doesn't hurt me, so think as you like.

Evan
09-02-2011, 08:17 AM
Also true of ball bearings, which develop a larger contact patch under pressure, and of roller bearings, which do the same..

The very major difference with a rolling element bearing is the difference in the curvature of the element to the race. The increase in contact patch under load is orders of magnitude less under load compared to a plane bearing. The plane bearing has the overwhelming advantage in lower force per unit area.

This isn't theoretical and it isn't "what I think". It is the reason that plane bearings are used for the heaviest loads.

jugs
09-02-2011, 09:27 AM
The very major difference with a rolling element bearing is the difference in the curvature of the element to the race. The increase in contact patch under load is orders of magnitude less under load compared to a plane bearing. The plane bearing has the overwhelming advantage in lower force per unit area.

This isn't theoretical and it isn't "what I think". It is the reason that plane bearings are used for the heaviest loads.


LIKE THIS (http://www.powertransmission.com/issues/0207/skf.htm) ??

OR THIS (http://cranetalk.com/ptc.htm) 2500 ton, sorry, can't find my link to a 3500 ton beast (all use rolling bearings)

aboard_epsilon
09-02-2011, 10:01 AM
LIKE THIS (http://www.powertransmission.com/issues/0207/skf.htm) ??
he he he ..all that devopment that goes into the bearing ..and when a bit of a gust of wind comes along...and you get gearbox failure

http://images.pennnet.com/articles/pe/thm/th_0708pef6t-photo-2.jpg


then .

http://jcwinnie.biz/wordpress/imageSnag/0102094952200.jpg

then

http://www.richarddows.co.uk/wp-content/uploads/2008/07/turbine2.jpg

all the best.markj

lazlo
09-02-2011, 12:00 PM
Here are plane bearings that are intended to run dry metal on metal.

http://bearing.firstbronze.com/viewitems/powdered-metal-bearings-and-thrust-washers/dri-plane-sleeve-plain-bearings.

Those are self-lubricating sintered bearings with dry (probably graphite or teflon) lubrication impregnated in them.

Self-lubricating bearings for pins/bushings and wear plates are very common in the mold industry:

http://img.directindustry.com/images_di/photo-m2/self-lubricating-plain-bearing-438640.jpg

lazlo
09-02-2011, 12:13 PM
A plain bearing MUST have a semi-line contact if dry...... otherwise it was a shrink-fit and not much good for a bearing.

it seems to be fairly well known that the oil is substantially pressed out after standing, and also that heavy loading (which presses out lube) causes wear.

The mechanics of a hydrodynamic (plain) bearing are really complicated. The bearing is riding on an oil wedge, which changes depending on rotational speed, the changing clearance of the bearing (due to manufacturing imperfection and wear) and the viscosity of the oil, which changes from the heat of the bearing. The oil swirls around the bearing in a very complicating oscillating pattern.

That's why precision hydrodynamic bearings have a lemon-shaped bore: to minimize the "oil whip" -- the random oscillation due to the oil movement.
That's the reason Richard Moore explains that they didn't use plain bearings in the Moore jig bores -- they couldn't get the oil whip down to the level of TIR they needed.

Spectraquest has a great white paper explaining the hydrodynamic effects. You have to sign-up to get the full paper, but it's free:

Effects of Clearance on Damping in Fluid Film Bearing
(http://www.spectraquest.com/tech/Effects_Clearanc_Damping_Fluid_Bearing.shtml)
http://www.spectraquest.com/tech/images/Effect1.jpg

When the shaft spins with an angular velocity of ω, the fluid is dragged into a convergent clearance. Due to gravity, eccentricity, manufacturing imperfection, misalignment, unbalance, and other factors, the rotor cannot always be perfectly centered. Therefore, the fluid forms a wedge (h1 is larger than h0 in Fig. 1) which generates pressure to support the applied load. By assuming velocity continuity, the fluid velocity on the surface of the journal is the same as the velocity of the journal (V) at the contact point, and is zero on the surface of the bearing. The fluid velocity distribution through the thickness is normally not linear, as shown in Fig.1. This is presumably caused by fluid loss due to end leakage. So the fluid flows not only in the radial direction following the rotating of the shaft, but also in the axial direction. As a result, the average velocity of the fluid is slightly less than V/2.

As the fluid friction is proportional to the viscosity as well as the velocity gradient, an increase in the running speed will increase the heat generation. On the other hand, lubricant’s viscosity is very sensitive to temperature. In the meanwhile, the dynamic parameters, namely stiffness and damping, are strongly affected by the fluid viscosity. Consequently, when a machine is speeding up, an increase in temperature will decrease the bearing stiffness as well as damping, which will further influence the dynamic behavior of the rotor system.

Evan
09-02-2011, 02:36 PM
Those are self-lubricating sintered bearings with dry (probably graphite or teflon) lubrication impregnated in them.

Not according to the manufacturer, especially since they are rated to 700f.


First Bronze offers a high performance sintered bearing called “Dri-Plane” using a proprietary metal compound for dry lubrication and/or high temperature applications. Contact the First Bronze “Dri-Plane” Bearing Specialist for more information.

Evan
09-02-2011, 02:53 PM
2500 ton, sorry, can't find my link to a 3500 ton beast (all use rolling bearings)

Look up the maximum capacities of plane bearings and get back to me. Some are used to earthquake proof large buildings such as the San Francisco Museum of Art.

macona
09-02-2011, 03:08 PM
Also what big telescopes ride on, pressurized oil bearings with phenolic surfaces.

lazlo
09-02-2011, 03:16 PM
Also what big telescopes ride on, pressurized oil bearings with phenolic surfaces.

That's a hydrostatic bearing. Basically, an air bearing with oil instead of air. Totally different animal.

Evan
09-02-2011, 03:20 PM
It's a type of Plane Bearing. They are properly called Plane bearings because even if the surface is curved it is considered to be planar in that it bears weight on area.

lazlo
09-02-2011, 03:25 PM
Those are self-lubricating sintered bearings with dry (probably graphite or teflon) lubrication impregnated in them.

Not according to the manufacturer, especially since they are rated to 700f.

"First Bronze offers a high performance sintered bearing called “Dri-Plane” using a proprietary metal compound for dry lubrication and/or high temperature applications.


http://www.reidsupply.com/GrpResults.aspx?pid=10021775&aitm=BNT-367&apid=10021775

New Dri-Plane® bearings are produced to the exact standards of our SAE 841 powdered metal bearings, however, they have a graphite-based dry lubricant built right into the walls of the bearings. There is NO OIL or GREASE needed for lubrication, therefore, cleaner with no out gassing, and can operate in temperatures -30F to +700F. They are ideal for furnace and oven applications. Also food processing and electrical equipment, exercise equipment, pharmaceuticals, vacuum processes, and glass manufacturing to name just a few.

Evan
09-02-2011, 03:29 PM
Graphite it is then. It's still a plane bearing that can run dry. The entire point of this is that plane bearing lathes will not suffer headstock damage from conventional knurling.

lazlo
09-02-2011, 03:33 PM
It's a type of Plane Bearing. They are properly called Plane bearings because even if the surface is curved it is considered to be planar in that it bears weight on area.

Call it what you want Evan, but there's very little in common between a hydrostatic bearing (i.e., an air bearing) which rides on a laminar flow of air or oil induced under pressure, and a hydrodynamic bearing which rides on an oil film.

jugs
09-02-2011, 06:16 PM
Look up the maximum capacities of plane bearings and get back to me. Some are used to earthquake proof large buildings such as the San Francisco Museum of Art.

In general -
For static loads - plain bearings
For heavy dynamic loads - rolling bearings (& sometimes hydrostatic)

For reduced vibration ( grinders etc) - plain bearings, with the correct viscosity lubricant, (a hydrodynamic bearing).

By the way - All bearings using a lubricant are in fact hydrodynamic bearings ( some are also hydrostatic ) [including ball & roller],as they are all riding on a wedge/wedges of lubricant, it's only the shear strength of the molecules of the fluid film that prevent metal to metal contact.

If any one wants to find the correct type of bearing for an application go to the experts - SKF, Timken, NSK, RHP, INA, FAG - It's just possible they may have more knowledge than a bunch of old farts arguing on a hobby forum.

Gravy
09-02-2011, 06:50 PM
If any one wants to find the correct type of bearing for an application go to the experts - SKF, Timken, NSK, RHP, INA, FAG - It's just possible they may have more knowledge than a bunch of old farts arguing on a hobby forum.

But what fun would that be?;)

Doozer
09-03-2011, 12:14 AM
"Their findings were it took exactly the same amount of side force on the spindle to raise the exact same size knurl, in the same type material, regardless of the type of knurler used."

I call your bullsiht. A scissor or pinch knurl tool places the majority of the force between the 2 knurl wheels.
And also, A cut knurl tool uses less force than a impression knurl tool.
Basic force vectors.
--Doozer