# Why don't they make metal gears ???



## rreiffer (Jan 14, 2009)

Hello all,

With all this talk of bad gears, etc., why don't they make metal gears instead of the plastic (or Delrin) ones? Is it purely a cost thing? At some point in time repairing hundreds of engines (i.e. Bachmann) you think it would be cheaper to put good gears in the critical sections? The cost of shipping the trains back and the labor for handling them (receiving, fixing and reshipping) must really add up at some point in time.

Does anyone know what it costs to make metal gears?


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## Greg Elmassian (Jan 3, 2008)

Cost, and noise... also I think that you need to be a little more attentive to lubrication. The cost is not only making the part, but assembling it, and how to fix it to a shaft. 

Remember the Ford Pinto example? Even though Ford knew about the danger of rear end collisions and the resulting fire incinerating the occupants, it was cheaper to pay the people who sued them than to fix all the Pintos. 

Likewise, apparently, the cost of the few people who stand up for their warranty is still less than fixing the problem at Bachmann. 

They are not the only company that has made what seems to be a foolish decision like this... USAT locos still crack axles and Aristo still has their locos wired by people who must be dyslexic or colorblind. 

Regards, Greg


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## Chucks_Trains (Jan 2, 2008)

MTH uses all metal gears, At least 10 year ago MTH made a statement that went something like "Why use plastic gears when metal only cost like .50 more?"


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## armorsmith (Jun 1, 2008)

As has been stated, cost is a negligible part of the equation. Noise is an issue caused by the root problem - Quality Control. To reduce/remove the noise using all metal gears, the fit of the gearing must be accurate, meaning the center to center dimensions must be held with in thousanths of an inch. Plastic gears allow a far greater tolerance before they become noisy enough to be audible. 

I still agree with others that it would be far cheaper in the long haul to do it right the first time than to have to do it over. 

My tuppence worth. 

Bob C.


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## George Schreyer (Jan 16, 2009)

Plastic gears, at least ones made with good plastic which Bachmann and others don't seem to use all the time, run quieter and actually wear less with less than adequate lubrication. The plastic is "more slippery" that metal. This doesn't mean that you can get by without lubrication, but in the case of light lubrication, the plastic gears actually wear more slowly. Also, all the wear in on the plastic gear which is arranged to be easier to replace. Few locos have plastic worms. If you want to protect one of the gears, then the worm is the one that is harder and more expensive to replace.


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## Torby (Jan 2, 2008)

And nylon gears hold up better. 

Course, Madam Mallet just chewed up a bunch. To Dr. Navin with her! I expect misaligned wheels had something to do with that, though she'd been running very smoothly.


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## Spule 4 (Jan 2, 2008)

Also in some applications, the gears are the sacrafice vs. some other mechanical bit in case of shock/lock up, etc.


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## BarrysBigTrains (Sep 4, 2008)

Metal gears, most properly need better lubrication, than plastic. BTW, when I say plastic I mean high quality plastic i.e.; Acetal, Delrin, etc. Most metal gear set ups arer in closed gear boxes, with grease or gear lube/oil inside. Those sets cost more than just the cost of gears.
I haven't had a gear failure in more than ten years, I follow a design philosophy which allows what I built to survive. I use metal gears and Acetal gears with brass hubs. Every gear has an oversized set screw which is used on a flat on the shaft to hold it in place.

A metal worm to an Acetal wormgear on the same shaft with an Aluminum spur gear driving an Acetal axle gear. All geared shafts in ball bearings, The motor is ball-bearing. 

Shaft spacing, for gear mesh has to be right.

I had my growing pains, and have been through five generations of drive design (curiously , the same as Bachmann's Big Hauler).

The mixed gear box is quiet, and will/does last years.

Barry - BBT


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## norman (Jan 6, 2008)

Maybe Bachmann should buy a Lionel 1960's O Gauge Atlantic loco and copy that drive. My Father did not oil any part of the Atlantic as I placed my 3 rail track on the carpet and of course oil spilling on the carpet would not have been appreciated by my Mother. I ran that Lionel non scaled Atlantic for hours on end at high speed. That locomotive drive was indestructible ! Even carpet fluff didn't both the gears. 

Norman


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## SE18 (Feb 21, 2008)

I pretty much have heard the same ideas George S. has given. I've got a couple of sort of related/unrelated questions. 

1. Can or should plastic and metal gears be mixed. By plastic I mean the high quality stuff. By metal, I assume most are brass. I've always heard that the gears closer to the motor should be the more durable type and the less durable going out toward the axle or wheel.

2. This second question is sort of unrelated to trains and more to scratchbuilding. Micromark advertises that it has real metal gears on the spindal shaft(?) of its lathes. If high quality plastic is used by another manufacturer, wouldn't that be just fine? 

Dave


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## Semper Vaporo (Jan 2, 2008)

Posted By SE18 on 14 Sep 2010 05:31 AM 
I pretty much have heard the same ideas George S. has given. I've got a couple of sort of related/unrelated questions. 

1. Can or should plastic and metal gears be mixed. By plastic I mean the high quality stuff. By metal, I assume most are brass. I've always heard that the gears closer to the motor should be the more durable type and the less durable going out toward the axle or wheel.

2. This second question is sort of unrelated to trains and more to scratchbuilding. Micromark advertises that it has real metal gears on the spindal shaft(?) of its lathes. If high quality plastic is used by another manufacturer, wouldn't that be just fine? 

Dave 

The mini- Lathes and Mills used plastic gears so there would be something "safe" to break if you took too big a bite into the work material and stalled the drive. I think the fear was that stalling the motor would result in a fire rather than the fuse blowing. Unfortunately, the gear that always shears off teeth is one that is extremely difficult to replace (ask me how I know!) and there is a definite risk of destroying the machine (cracking the cast-metal body, or damaging the ball bearing races) while doing the replacement (you have to drive out some large bearings and then drive them back in and the design is not conducive to doing that). 

I think that over the years this ONE "original" design for the drive train, motor and motor controller used by all the various manufacturers has been improved by each different manufacturer to the point where there is less risk if the motor is stalled. Also, although they advertise that they are using metal gears, there is still one plastic gear in the train that can shear a tooth if things get bound up; and that one gear is extremely easy to replace (remove the top dust cover and remove one bolt). But I doubt if that gear will ever shear as the torque on it is very low (it is high speed, not high torque, where it is in the gear train).

The last time I sheared off one of the gears I bought the metal replacement gears (from LittleMachineShop.com), but because I had a set of plastic replacement gears in the drawer (don't want to have to stop operations for a week or more waiting for replacements), I won't be putting in the new metal ones until the NEXT time (there is no way I am going to risk destroying the machine without being in REAL need of replacing the gears at the time!).


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## SE18 (Feb 21, 2008)

thanks for your real life insights; very informative


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## BarrysBigTrains (Sep 4, 2008)

One of the lessons learned, is that the driving gear must be stronger (material) than the driven gear. So my worm is brass, driving an Acetal gear on a shaft with an Aluminum spur gear driving and Acetal axle gear. 

Beautiful. 

Barry - BBT


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## RimfireJim (Mar 25, 2009)

1. Can or should plastic and metal gears be mixed. By plastic I mean the high quality stuff. By metal, I assume most are brass. I've always heard that the gears closer to the motor should be the more durable type and the less durable going out toward the axle or wheel. 
For a speed reduction gear train as used on our model locomotives, the torque on a gear goes up as the speed goes down as you progress through the gear train from motor to drive axle. Load on a gear tooth is proportional to torque, so the gear at the axle sees the highest load. But don't confuse load with stress, which is load divided by area. Stress is what causes mechanical components to fail, when the stress exceeds the material strength. A properly designed gear train will have stresses on each gear at a reasonable percentage of the strength of the material for that gear, combined with factoring in some other things like the number of teeth sharing the load. 
Gear train engineering, including material choice, center distances tolerance, use model, cost, etc. is one of the more challenging aspects of mechanical engineering. It's not too surprising that we see failures in some of these products, but it is bothersome that they don't get fixed in the next offering from the same manufacturer.


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