Now what!!! NWSL gearbox issue
#1
Finally, got all my NWSL parts together for my gear box conversion on my Bowser H-9. I have assembled everything and installed into the frame. I set up the frame on a stand to test for binding or other problems and break in. I found the "other problem", when testing the assembly about 10 min in the worm gear shaft becomes hot, very hot and causes the reciever cup to melt and fail. Anyone have any thoughts on this?

Mark Curse


After I made this post I took gearbox apart and found some brass flakes floating around in the grease/oil. I know this is not good. Closer examination reveals scoring on the worm gear shaft, who knows what's in the bushing. Question now being would It be wise to replace the whole gearbox or just clean it out? I'm leaning towards replacing it. Let me know if you share the same thoughts.

Mark Wallbang
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#2
Reckon I would replace it.
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#3
:o That reminds me I have two gearboxes on order that haven't come in yet. Guess it's a good day to get to my local hobby shop and check on that order !! Thanks !!
OH, I would seriously consider replacement.....something doesn't "add up", and it could become a constant "issue".
We always learn far more from our own mistakes, than we will ever learn from another's advice.
The greatest place to live life, is on the sharp leading edge of a learning curve.
Lead me not into temptation.....I can find it myself!
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#4
It's odd that any shaft would be scored, as they're almost always steel - not likely scored by brass or plastic, anyway. I'm unclear as to the shaft to which you're referring, though, as there can be some confusion in the terminology. A worm gear is the gear driven by the worm, and it may be pressed onto its short shaft or, in some cases, be a loose fit on the shaft and simply rotate on the shaft. The worm shaft on many older locos was an extension of the motor shaft, and while the shaft was invariably steel, the worm itself could be steel, brass, or plastic. Even if there's a separate drive train (plastic u-joints or flexible tubing) between the motor and worm, the worm shaft would be steel.
In a gear set-up where there's only a worm and a worm gear, the worm itself is usually steel and the driven gear brass, or the worm brass and the driven gear plastic or fibre. The thinking behind that is that the softest gear should be the one easiest to replace.
On an idler gearbox, there's an additional gear (or gears) introduced between the worm and the axle gear. This type allows greater reduction (and often a straighter driveline between motor and worm), and the worm and axle gears will be the harder ones, with the idler made of softer material because it's the easiest, by far, to replace.

I'm surprised that 10 minutes of break-in running could generate that much heat, though, and I'm wondering if the drive is all-metal direct from the motor to the plastic gearbox. Is it possible that the motor is overheating, and the heat transfering through the metal parts to the plastic gear casing.
The only other cause which springs to mind is that something was damaged during construction - perhaps a shaft scored when pressing a gear onto it, then the scoring damaging the bearings and/or the gears. Any foreign material in a gearbox will damage anything which is of a softer material.
Any chance you could post a photo of the set-up of the motor/drive assembly?

Wayne
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#5
OK Wayne, It took me a little while to figure out how to upload pictures to The Big Blue website. I think I got it figured out now so here goes. The NWSL gearbox I used was NWSL 142-6. It comes with 1 worm(steel) 2.4mm shaft, 2 wormshaft bronze bearings, 1 28 toothgear (delrin), 1 28 tooth axle gear (brass), 2 gearbox sides, 1 bottom cover, thrust washers and screws. The steel shaft(worm) is what I noticed was hot. I did not consider that the motor was hot, it didn't feel any hotter that I would normally expect. I used the proper cup and ball universal joint to connect the motor to the gearbox. Here are some of the pictures:

First one is set up in the frame:[album]4617[/album]




second one is gearbox assembled with out drivers attached[album]4616[/album]

third one is with side removed revealing delrin wormgear/idler gear[album]4618[/album]

Fourth is worm shaft with bearing removed on right side. Notice black rings about 1/4" from worm. Bearing was a little difficult to pull off and close inspection which photo doesn't show(camera limitations) is small groves in the shaft.

[album]4620[/album]


Hope, you could offer some help with this,

Mark
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#6
Your set-up on the loco looks good, with a nice straight line throughout the drive train.
Mostly just guessing here, Mark, but my first question concerns the scoring on the shaft. Do the grooves go around the shaft (like rings), or are they longitudinal? If the latter, they may have been caused when the worm was pressed onto the shaft - perhaps a burr in the bore of the worm. If you fitted the worm to the shaft, was the shaft clamped in a vise, with the jaws perhaps marring the surface of the shaft? That usually causes a minor displacement of material which causes a ridge and a groove - material displaced from the groove forming the ridge. That can be cleaned-up by chucking the shaft in an electric drill (don't allow the jaws of the chuck to damage the shaft, though) Misngth then using a finely-cut file or emory cloth to remove the ridges as the shaft spins - the grooves shouldn't cause any problems. If the bearing is damaged, you should be able to get a replacement from NWSL.
Was it the gear case which was damaged by the heat? If so, it would likely have been where the bearing was seated, and in that case, you should probably replace the whole gearbox, as the alignment will likely be off. NWSL may provide replacement parts, as I've found them to be very accommodating, and especially so if the problem was caused on their end.
Another source of heat could be the thrust washers - while you don't want a lot of slop in the drivetrain, they can also be too tight, with the result that the bearings are attempting to rotate, perhaps intermittently, with the washers and the worm. You can thin a thrust washer by sliding it back and forth over a piece of fine sandpaper - only a couple of thousandths of play will be enough to prevent that scenario, but be sure to clean the washer before putting it back into the gearbox.
The only other issue I can see is the shaft protruding through the front of the gearbox - nothing wrong with it doing so unless there's a chance that it may strike something on the loco's frame or something else once the boiler is installed .

Wayne
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#7
Wayne, the scoring was rings around the shaft as if a foriegn object was in the gearbox. As I stated before I did find some brass chips in the gearbox when I opened it up. I agree that the brass is a softer metal then steel, but stranger things have happened. Another thing I thought of was when I cut the shaft there could have been a steel burr left on the shaft that I missed when cleaning which could have caused the scoring.The part that failed was the reciever cup from the universal U-joint kit (NWSL 488-6) as a matter of fact, 2 failed. I thought the same thing about the shaft extending out the nose end of the gear box, but I can't see it rubbing on anything. Anyway I ordered a new one from NWSL over the weekend. I'll probably give Dave a call tomorrow and see what he thinks.


Thanks for your insight,

Mark
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#8
Mark
Have you tried contacting NWSL: Dave Rygmyr NorthWest Short Line (<!-- w --><a class="postlink" href="http://www.nwsl.com">www.nwsl.com</a><!-- w -->) Dave was a big belp in trying to regear a Bachmann doodlebug.
Andy Jackson
Santa Fe Springs CA
ATSF/LAJ Ry Fan & Modeler
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#9
Andy , I had planned to do that today but didn't have time at lunch to give him a call. I'll try him tomorrow. He's already been a big help already. And NWSL has one of those oops proof guarantees. But I have ordered a new one, but I also have plenty other Bowser kits that will take the same gearbox.


Mark
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