Bearings: Why not simple round tubes?

[mmagliaro]

The "accepted standard" in really good running steam loco bearings seems to be
little square shaped phosphor bronze bearings with "ears" to hold them in the frame slots.

So I'm wondering.... Why not just a simple short length of phosphor bronze tubing?
It would sit in a slot in the frame and the axle would spin inside it.  Let's assume it is placed so it can't
slide all the way out of the frame.  (It could have little tabs on it, or there would simply be an axle tube
in the middle of the axle like I'm thinking for my 0-6-0 project, so the bearing tube could only move back
and forth a little between the axle tube and the wheel back).

Is there something inherently bad about a round bearing?
(I'm expecting Victor to chime in here, because I think he has groused about round bearings before,
like the ones in the Con-Cor 2-10-2, but I don't exactly see what's wrong with them).

[loyalton]

A couple of points:

How much play does one allow for a sleeve bearing of a certain length? It needs some to allow going around curves, more than just side-to-side I would think. Does one allow some small amount of float to the whole bearing/axle assembly?

The phosphor bronze bearing tube will, I'm sure, need lubrication. The spinning axle will move grease out of the tube, for one. Potentially messy. Then also, how does one re-lube the axle/bearing assembly easily? Maybe a switch to acetyl plastic is needed. There are different formulations, so ideally we'd want one that will take wear for (hopefully) the lifetime of the engine. Or we'd want a design that would make the bearings an easy change-out.

[hminky]

Bowser used round bearings with a flange on their HO Northerns.

http://www.bowser-trains.com/hoother/Partref1.pdf

Part 15011 under "B"

Harold

[Chris333]

They are square so the axles spin in the bearings and not the bearings spinning in the frame.

My favorite HOn30 loco builder makes his own square bearings:
http://s276.photobucket.com/user/jnj1097/library/Axle%20bearings?sort=3&page=1
Last I heard he was looking into a 3D bearing that was only square at the top. He would 3D print then cast in brass.
Similar to these:
http://s276.photobucket.com/user/jnj1097/media/model%20train%20stuff/ab3_zps671bc0b8.jpg.html?sort=3&o=2
http://s276.photobucket.com/user/jnj1097/media/model%20train%20stuff/ab1_zps0e81f12b.jpg.html?sort=3&o=0

[Lemosteam]

Yeah, why not?  One of the most free rolling chassis is still the Minitrix K4; still running after how many years?

[garethashenden]

A couple of points:

How much play does one allow for a sleeve bearing of a certain length? It needs some to allow going around curves, more than just side-to-side I would think. Does one allow some small amount of float to the whole bearing/axle assembly?

The phosphor bronze bearing tube will, I'm sure, need lubrication. The spinning axle will move grease out of the tube, for one. Potentially messy. Then also, how does one re-lube the axle/bearing assembly easily? Maybe a switch to acetyl plastic is needed. There are different formulations, so ideally we'd want one that will take wear for (hopefully) the lifetime of the engine. Or we'd want a design that would make the bearings an easy change-out.

Well first of all, you use oil not grease. Not too light, otherwise it will flow away. To top up the oil a small hole is put in the middle of the bearing tube.

Brass tube bearings with steel axles have been used in larger models by some scratch builders for decades. Some of these engines have done many real miles without much wear.

[mmagliaro]

In answer to the questions about lube, lateral play and up/down play, the answer is "yes" to all of them,
but it's the same answer you have with square bearings in tabbed frame slots.  They do get lubricated,
and they do need some up/down as well as side-to-side play... but not very much ... to allow for
track and frame imperfections.  The lateral play isn't as important, since the axle should be able to slide
side-to-side for curves.

I dig Chris's answer about not wanting the bearing to spin in the frame, which it very well might if it's just sitting
in a channel in the frame.  Okay... so a tube with a couple of flatted sides on the outside to keep it from spinning
in the frame slot.

Now.. what is the purpose of the little "ears" that keep the square bearings trapped in the frame? 
I suppose to me it seems like they are a good idea just to keep the bearing from wandering too far in or out.
If the bearing itself were long enough, it couldn't wander because it would be trapped between the back of
the wheel and the axle tube.  THAT, however, would require a longer bearing, with more contact surface on the axle, resulting in a lot more friction than a slim little bearing.

(And in case anyone is wondering... I'm thinking about this because the high resistance of the ball bearings
I wanted to use for my engine rule them right out of the question.  Even if they do "sorta work" when
6 of them are in a frame, giving up 20 ohms or more in the bearings is not acceptable to me.  0.1A x 20 ohms = 2 volts,
and that's a lot of drop, and depending on at least 2 of them to be making contact at  every instant so
that the voltage drop is halved is a bad gamble to be designing against. This is an especially bad compromise for
a contact point that is close to 0 ohms in a friction bearing.)

[peteski]

One important property of those typical model RR bearings not mentioned yet is that good quality friction bearings in model locos are made from sintered brass or phosphor bronze.  Similar to the bearings used on the motor shafts of pretty much every small DC motor used in N scale.

The porous structure of the metal acts like a sponge and holds the lubricating oil in much larger quantity than a solid metal bearing.  That greatly reduces the need for periodic lubrication.

Also it is important that the bearing and the shaft suspended by the bearing are made from dissimilar materials.

[sizemore]

Now.. what is the purpose of the little "ears" that keep the square bearings trapped in the frame? 
I suppose to me it seems like they are a good idea just to keep the bearing from wandering too far in or out.

Up and down play (answered). Side to side play (answered). And vertical rotational play. Think of it like toe in/out on a wheel. If the bearing toes in or out it can bind on the axle.

Humbly Submitted,
The S.

[mmagliaro]

Most loco bearings actually hold a nub on the back of the wheel rather than the thin axle itself.  I can see how
there's enough slop in there to possible let the bearing toe in or out and bind.

But I'm planning to run the axle itself through the bearing (like the ultra-low-friction Kato GS-4 design), and
I will have as near a zero-tolerance fit as possible.   The width of the bearing will be at least as much as the diameter
of the axle (1.5mm).  So I don't expect a problem there.

[narrowminded]

If you double flanged them with a grooving tool and the bearing width was greater than you liked, bore a small oversize, maybe .005", to remove any excess bearing width.  Also serves as an easy wear inspection.  You'll be able to see the relieved bore disappearing with the naked eye if wear ever did occur.  As far as making them square, start with square bar mounted vertically in your vise and use a saw to chase around them in your mill.  Part them off with the same saw.  A square block would allow for the axle pocket to be just an end mill cutting a square bottomed pocket which might afford some easier options for machining the features needed to place coil springs on the top. Those would serve not just to aid the axle float, maintaining better wheel to track contact, but also affords a direct power pickup from the bearing to the frame, eliminating one more flakey electrical contact point.  Springs can be made very precisely in your lathe by winding on an arbor of the ID size you'd like (probably a music wire size) and the appropriate thread for the coil spacing, then wind the number of turns (probably by hand for this little stuff), drop the half nuts out when you've turned the needed number, finish the half wrap for a flat end, and done.  Keep the wire tight to the arbor and following the bed travel precisely with a vee notched guide mounted in the tool post, holding and guiding the wire snug on the arbor. 

I have used each of those methods at one time or another over the years and on my current project have relieved bearings in several places with a bearing counterbore or shaft undercut just to reduce the bearing area. In scale my bearings were GROSSLY oversized for the duty which just added unnecessary friction, even from just the shearing of the oil in them.  Did you ever notice the extremely crude fit on gear pins, axle bearings, universal joints, etc throughout these locomotives we see?  It's a cost thing for sure but they still get generally acceptable performance for the service and mainly because those terrible fits can be tolerated due to GROSSLY oversized components (for the loads seen) that really don't need to be better and in fact, at times, only create the exact problem that is being addressed with fixes like relieving bearing bores. Too much friction. The mass produced stuff we see gets their relief by having a 3/8" hole for a 1/8" shaft.   Good luck with this.  I get a sense you're having fun with the challenge.  It's fun to hear your trials and tribulations but also seeing some very impressive successes.