# Thoughts on bearings verses oilite bushings for loco drives?



## Michael Glavin (Jan 2, 2009)

I’ve been working on rebuilding a well used old Aristocraft Pacific drive for a freind. Upon disassembly I found the axles (deep grooves) and gears were damaged as well as notable wobble in the drivers when spun on my lathe. The loco weight is supported by thin brass washers in lieu of a more typical olite bushing or bearing at the axle interface. IMO this is a very poor design, typical bushings/bearings shoulder the load with more mass or surface area to displace the load which in turn mitigates wear and tear on the axle. I believe this drive was the first design of ultimately three drives of which two utilized the aforementioned brass washer/bearing and brass axles. Brass on brass is not a good combination. The second drive used steel plated axles presumably to realize a longer life. 

So I think why not use ball bearings? First problem realized is the stock brass bearing/washers are not a standard bearing size. So what to do, machine bushings or enlarge the housing bore for standard sized metric bearings. I decided the best approach was to enlarge the housing bore which will provide over the counter parts and reasonable bearing surface area, 6mm ID and 10/12mm OD.

All right then I proceed to ponder the best method to enlarge the housing bore, problem is the injection molded housings of Engineers plastic are not suited to be fixed in place easily for machine work and all three housings are different too. Luckily I had a few drives of the first generation to experiment with. Turns out the best method of reaping repeatable accurate results would require making fixtures to hold the three housings (front-center-rear axle housings) which could be fixed to a mill X-Y table. This wasn’t to painful but the results first garnered were not acceptable to me, upon mating housing halves the bores were not perfectly in line. So me thinks the best approach is to mate the housings and line bore them as an assembly. A new fixture was machined and this worked well. One problem I encountered was the Engineers plastic machinabilty, while machining the plastic was effortless and worked well the clearances garnered were somewhat different than expected. Typically I’d allow three thousandths oversize or so for the bearings interference fit with metal housings, NOT for plastic undersized cuts were needed to realize the required bore diameters. In trying to standardize and simplify the effort I purchased end mills of the anticipated size requirements for the bearings utilized verses a more complex set-up with an adjustable boring tool and centering same over the ‘Z’ axis. I should have determined the actual required end mill size first with the boring tool and experimenting with same, lesson learned! The only problem with a boring tool is the extended length to reach through the housings (I had to order an extended length cutting tool). While waiting I tried again with a fixed end mill in combination with a rotary table, this allowed me to machine the housings to the right inside diameters but left me wondering what size end mill would perfect and simplify the effort.

When I first thought about using bearings I considered what effect on electrical conductivity, electrical losses and or pick-up would be through the drivers/axles/bearings. I decided to tread on and experiment and simply see what results were garnered. In the back of mind I assumed quality locomotives used ball bearings to support the load on the axles.

Today I noted in a post about Accucraft Cab Forwards; the journal boxes for same were simply brass (albeit thick brass) so I came to the conclusion that ball bearings might not be the answer!

Can anyway share experiences with ball bearings on loco axles? Presumably on LS models electrical losses are a moot consideration, what about maintenance? Are ball bearings problematic in this application? Do brass or oilite bushings offer any advantages over ball bearings?

Michael


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## Mr Ron (Sep 23, 2009)

Instead of trying to mill plastic, I would try to fabricate from metal a frame that would fit inside or replace the plastic frame. That would make it much easier to maintain alignment. I think using ball bearings would make the problem of alignment more difficult. Model locomotives are made to loose tolerances to prevent binding. You may cause binding if you try to get tolerances too small. In the locomotives I build from scratch, I use only UHMW plastic bearings or oilite bearings. I build in 1-1/2 to the foot scale where tolerances are not as critical as they would be in a smaller scale.


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## Mr Ron (Sep 23, 2009)

Posted By Mr Ron on 20 May 2010 09:15 AM 
Instead of trying to mill plastic, I would try to fabricate from metal a frame that would fit inside or replace the plastic frame. That would make it much easier to maintain alignment. I think using ball bearings would make the problem of alignment more difficult. Model locomotives are made to loose tolerances to prevent binding. You may cause binding if you try to get tolerances too small. In the locomotives I build from scratch, I use only UHMW plastic bearings or oilite bearings. I build in 1-1/2 to the foot scale where tolerances are not as critical as they would be in a smaller scale. Unless ball bearings are well protected, any spec of grit would cause trouble and premature bearing failure.


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## Michael Glavin (Jan 2, 2009)

Ron, 

Thanks for your thoughts. While I agree metal components would allow for more exacting tolerances; my goal was to work with what was already in play. In the future I am going to fabricate some gear-boxes and or drives, I'm simply waiting to garner some experience with CNC retro-fits on my mill, lathe and router. 

I've dedcided to assemble one drive with ball bearings and a second with "oilite" bronze bushings, maybe I'll learn something... 

Regards, 
Michael


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## noelw (Jan 2, 2008)

Michael. Quote.......... 
When I first thought about using bearings I considered what effect on electrical conductivity, electrical losses and or pick-up would be through the drivers/axles/bearings. I decided to tread on and experiment and simply see what results were garnered. In the back of mind I assumed quality locomotives used ball bearings to support the load on the axles. 
............................................................................................................................................................................................................. 
To keep the electirical conductivity down on bearing you can put wipers on the inside of the drivers rims and mounted on top of the motor block. I did that on a C-16 and some on Steam Ho engs. Also wipers on tender wheel to help out to. 
Aren't the bearing on wheels sets for rolling stock have sealed bearings? Ones on my Batt. car has. 

Swing by sometime in the area and i'll show you some i did on the Ho engs. Later guy..Replacing sound card on Hp/puter that went snaple, crack and poof.. hahahaha.. Using Gateway for now..


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## lownote (Jan 3, 2008)

Aristo uses ball bearings in the most recent version of the pacific drive (the "prime mover" gearbox they use in other locos as well), but they are cereamic balls and don't conduct. Conductiuon is a little flaky as a result. Greg Elmassian's site has a lot of detail on this. Greg also makes the argument that you don't want high current going through ball bearings, as they will pit and oxidize.


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## Michael Glavin (Jan 2, 2009)

Noel, 

The bearings I have on hand are sheilded, which is better than an open bearing however they are not sealed. Sealed bearings would be better I suspect. 

Michael


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