Screaching Bearings- Astonishing Effects

[u18b]

After an exhausting time of tinkering, tinkering, tinkering....
I finally got my surplus Wiseman Shay kit to run acceptable.   (I'm not the original owner and I'm picking up from someone else's work).

This is a complex model that was a basket case when I got it.  Almost every subsystem required tinkering/adjustment or even rebuilding.



I would get it quieter... then tinker... then worse... then tinker.  etc.

My point is that excess noise was coming from multiple problems.

In this photo (ignore that the worm bearing mount screws have been removed)...  notice that in this photo alone (not even showing all that stuff happening at the trucks and crankshaft) we have a worm, washers (too many/not enough?), 1 gear soldered to shaft, 1 gear retained by screw (screw too tight/too loose? need a washer? no washer?), 2 bearings, tubing for interface (which is not even), and a poorer quality Bachmann motor (probably 3-pole).   Noise could come from any or all of these sources.   All total in the whole loco, there are about 20-30 points where noise could be produced.



I had binding issues, whirring noises, screeching noises, cogging issues, and mesh issues...  all painstakingly corrected.
But no matter what I did, I could not get it to run to my standards.

So then I moved toward drastic measures.      I decided on a progressively challenging course.  Start easy and then move to the really hard.
1.  Replace the motor and motor/worm shaft interface
2.  Replace the worm and bearings
3.  Rebuild the crankshaft   

Thankfully I had some spare parts.

So I replaced the motor... and while replacing the worm, made an astonishing discovery.

The screeching was mostly coming from one bearing- the inside worm shaft bearing.

But what was astonishing was how the steel shaft was damaged by the screeching bearing.  This is what surprised me. 

I fact, the damage was so bad, you could actually see it.



So I decided to put my caliper on it and take some readings.

The steel shaft is a 1mm shaft.  So the right end where the coupling was soldered is still stock.

Two of the friction/moving surfaces have been worn down around 1/100th of an inch  a millimeter (or possibly only 5/1,000ths since the digital caliper  only goes to two decimal places and thus rounds up or down).

But the spot where the screeching bearing sat has been worn an EXTRA 4/100ths of an inch! a millimeter   That may not sound like much but remember this does not even count how the bearing hole has been opened up also.



So when a bearing is screeching, you automatically think about how the soft bronze/brass bearing will be damaged.    But I never gave much though to how the harder steel shaft could be damaged as well.

So in the future, maybe this post will help make real to everyone in a memorable way the admonition:   If you hear screeching, STOP and fix it.   Never keep running screeching bearings.

EDIT:  Corrected egregious brain fog   

[peteski]

Thanks for this write-up Ron - very educational.

[milw12]

This reminds me of some fan shafts I've had to replace, say a bad bearing like yours, poor alignment, excessive vibration etc. You can get a solid steel shaft with a deep groove that almost looks machined- 1/4" deep or more depending how long it had been running. Granted the torque and load are much higher than a model train, but I'll leave the physics for those in the know. All I know is that when I see it, I order a new shaft and bearings and align/balance everything properly 

Lucas

[mmagliaro]

.040" is a HUGE amount of wear on that shaft. 

Are you sure that shaft is really hardened, like a drill bit?  Maybe it's not and that's why it wore so much. 
You've shown the evidence, so there's no doubt that it wore down.  But it's still pretty hard to believe that grinding hardened steel against a brass bearing would make the steel wear at all.

I wonder now, if I took a piece of drill shaft, put it in a power drill, and just ran it against a piece of brass, would that steel shaft wear down like that?   Maybe worth an experiment.

[C855B]

I can believe it. Dried lubricant and even powdered brass can make for quite an abrasive. Way back in the last century when I was rebuilding car engines, the bearing surfaces against the crankshaft steel were a soft alloy ("Babbitt metal") designed to take the brunt of the wear and be the renewable component. Nonetheless, I had to replace more than one crankshaft because it was worn past the allowable re-machining tolerances. Yes, it was a little more complicated than that (recirculated dirty oil being the bigger wear factor), but same effect as what Ron found.

[u18b]

.040" is a HUGE amount of wear on that shaft. 

Are you sure that shaft is really hardened, like a drill bit?  Maybe it's not and that's why it wore so much. 
You've shown the evidence, so there's no doubt that it wore down.  But it's still pretty hard to believe that grinding hardened steel against a brass bearing would make the steel wear at all.

I wonder now, if I took a piece of drill shaft, put it in a power drill, and just ran it against a piece of brass, would that steel shaft wear down like that?   Maybe worth an experiment.

I have no idea if it is hardened or not.
How would you tell?

[peteski]

.040" is a HUGE amount of wear on that shaft. 

It is not 0.040" but it is in millimeters. 
Looking at the photo of that 1mm diameter shaft's wear, it looks more like 0.04mm.  I also think that always using the leading zero on fractional dimensions makes things look clearer.

If 1mm shaft was worn by 0.4mm then it would be almost half its original diameter (0.6mm). That shaft in the photo does not look anything like that.  Let's look at that photo everyone.

[u18b]

Yep.
Brain fog- I switched systems (NASA lost a Mars probe for the same reason).

All is in millimeters.  Thanks Peteski.

I corrected the original post.

But the original point is that-
1.  The shaft wore noticeably down
2.  .04 mm is a huge amount (combined with the damaged bearing) and will cause a bearing to scream.

[mmagliaro]

Whoops... sorry.  Yes, .04mm, which is  only .0015"

[woodone]

Well from the looks of things that worm drive was in need of some well deserved TCL.
Not sure where your noise was coming from? The wear on the shaft is due to metal debris that worked its way into the bearing. The very fine metal makes excellent cutting compound! That shaft would not wear like that without the grime to cut the shaft.
There are many problems in this set up. Get a free floating U-joint between motor and worm shaft. Right now I would guess that coupling is vibrating and was putting some strain on that front bearing. 
I would make some new bronze bushings and some new bearing supports. Might has well replace the shaft and get some way to adjust the worm to its worm wheel.
Looks like a project, but well worth the effort!
,

[u18b]

Thanks Woodone,
I've already made a lot of changes.   Will post for Weekend update.

[Iain]

It also appears that you had some galling (hence the shiny).

[Doug G.]

The worm, itself, is damaged from poor mesh, too. The telltale sharp edges.

Doug

[peteski]

The worm, itself, is damaged from poor mesh, too. The telltale sharp edges.

Doug

I wonder if the worm gear is also brass? Hard to see, but it might be. That would likely cause excessive wear.

[jj3]

A simple test is to take a mill file across it, if it takes metal off it's not considered "hardened". Otherwise you can use a hardness tester, but it will leave a divot. I have one sitting next to me

I have no idea if it is hardened or not.
How would you tell?