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Substandard plastic


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Hi all,

 

I am gradually putting in dcc chips in all my locos and running on the layout, these locos are not particularly old but I have found many that have had issues in the center cog of a wheel set split, which I now have quite a few spares to replace them. I have now found my first split cardon shaft, in fact both of them are split. I did try glueing them on but I tried every type of glue without success as the bearings just slip on the shafts. So why do manufactures still seem to use plastic that fails in this manner?

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1 hour ago, Andymsa said:

I did try glueing them on but I tried every type of glue without success as the bearings just slip on the shafts

Did you try the 'superglue and baking powder' method? I've found this to be about the strongest, with the advantage that you can file the glue once it's hardened.

 

Ian

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37 minutes ago, ISW said:

Did you try the 'superglue and baking powder' method? I've found this to be about the strongest, with the advantage that you can file the glue once it's hardened.

 

Ian


 

I did try super glue on its own, I do have a powder that goes with it to thinker it up into a paste, so I assume that’s what the baking powder is for? The real issue is super glue won’t stick to the shiny metal shaft.

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10 hours ago, Andymsa said:

The real issue is super glue won’t stick to the shiny metal shaft.

I'd have thought that some gentle sanding would introduce sufficient 'scratches' into the metal surface for the glue to adhere.

 

Ian

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Split gears are a common problem with the spur gears used on pancake driven 80s locos but you say yours are not particularly old, and that several have failed.  That suggests another sort of problem to me; operating and driving practice.  Automated operation, sudden jerky starts and stops, kids operating and throwing the reversing switch while the loco is moving forward, small children attempting to use the locos as pushalong toys put strain on the gear trains that they are not really designed to cope with; if any of the above might apply to your layout, it needs taking into consideration.  Slow, smooth, starts, gentle acceleration and deceleration, and smooth stops will reduce wear on your gears and enhance the longevity of the model as well as looking more realistic.  A visit to any exhibition, when they start up again, will reveal many experienced and capable modellers who are in fact appalling drivers of model trains!  Having had several Mainline locos sent to early graves with split gears and quartering issues back in the 90s when I was a member of a club by another member's poor operating practices, I have an axe to grind here!

 

Strain can be put on to drive trains of cogs and spur gears by running the model around sharper curvature than the manufacturer recommends as well.  The loco manages the curve, but sideplay is taken beyond the design limit and a gear that might already be weakened by previous passage over the curve will eventually crack.  Lubrication may need thinking about as well; models are supplied new with a silicone grease that can harden over time and become the very opposite of lubrication, and if it is replaced with a mineral oil based product, chemical reaction can make the nylon the gears are made out of brittle and prone to cracking; use a non-mineral oil based product, sparingly.

 

Why do manufacturers not use more reliable brass or tungsten gears?  Cost (and maximising profit), obviously, but also because nylon has a small amount of 'give' in it which, unless the system is abused in the ways described above, enables closer meshing and more efficiency from the motor, especially when running slowly with DC, when the current is at it's lowest; it is a part of the smooth running we have come to expect from RTR mechanisms these days.  Modern motors are low current consumers, which is necessary for DCC operation.

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11 hours ago, Andymsa said:

i did try that didn’t seem to make any difference 

It was worth a try. I have managed to successfully glue a Hornby metal pinion gear onto a CD-ROM metal motor shaft using superglue (without baking powder) on 2 occasions. In both cases there was actually a small gap to fill with the glue. This method followed what I saw in a YouTube video, so the method is probably quite common in the CD-ROM motoring of Hornby ringfield fitted engines.

 

Ian

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5 hours ago, The Johnster said:

Split gears are a common problem with the spur gears used on pancake driven 80s locos but you say yours are not particularly old, and that several have failed.  That suggests another sort of problem to me; operating and driving practice.  Automated operation, sudden jerky starts and stops, kids operating and throwing the reversing switch while the loco is moving forward, small children attempting to use the locos as pushalong toys put strain on the gear trains that they are not really designed to cope with; if any of the above might apply to your layout, it needs taking into consideration.  Slow, smooth, starts, gentle acceleration and deceleration, and smooth stops will reduce wear on your gears and enhance the longevity of the model as well as looking more realistic.  A visit to any exhibition, when they start up again, will reveal many experienced and capable modellers who are in fact appalling drivers of model trains!  Having had several Mainline locos sent to early graves with split gears and quartering issues back in the 90s when I was a member of a club by another member's poor operating practices, I have an axe to grind here!

 

Strain can be put on to drive trains of cogs and spur gears by running the model around sharper curvature than the manufacturer recommends as well.  The loco manages the curve, but sideplay is taken beyond the design limit and a gear that might already be weakened by previous passage over the curve will eventually crack.  Lubrication may need thinking about as well; models are supplied new with a silicone grease that can harden over time and become the very opposite of lubrication, and if it is replaced with a mineral oil based product, chemical reaction can make the nylon the gears are made out of brittle and prone to cracking; use a non-mineral oil based product, sparingly.

 

Why do manufacturers not use more reliable brass or tungsten gears?  Cost (and maximising profit), obviously, but also because nylon has a small amount of 'give' in it which, unless the system is abused in the ways described above, enables closer meshing and more efficiency from the motor, especially when running slowly with DC, when the current is at it's lowest; it is a part of the smooth running we have come to expect from RTR mechanisms these days.  Modern motors are low current consumers, which is necessary for DCC operation.


when I have found these issues the locos are brand new and have never been run apart from when they were brought for testing they were ok. On this occasion it appears to be a quality of the plastic used and age. When I stripped the loco I did find the gear assembly covered in grease ( manufacture applied) which had got onto the cardon shaft which obviously degraded the plastic.

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11 hours ago, The Johnster said:

Split gears are a common problem with the spur gears used on pancake driven 80s locos but you say yours are not particularly old, and that several have failed.  That suggests another sort of problem to me; operating and driving practice.  Automated operation, sudden jerky starts and stops, kids operating and throwing the reversing switch while the loco is moving forward, small children attempting to use the locos as pushalong toys put strain on the gear trains that they are not really designed to cope with; if any of the above might apply to your layout, it needs taking into consideration.  Slow, smooth, starts, gentle acceleration and deceleration, and smooth stops will reduce wear on your gears and enhance the longevity of the model as well as looking more realistic.  A visit to any exhibition, when they start up again, will reveal many experienced and capable modellers who are in fact appalling drivers of model trains!  Having had several Mainline locos sent to early graves with split gears and quartering issues back in the 90s when I was a member of a club by another member's poor operating practices, I have an axe to grind here!

 

Strain can be put on to drive trains of cogs and spur gears by running the model around sharper curvature than the manufacturer recommends as well.  The loco manages the curve, but sideplay is taken beyond the design limit and a gear that might already be weakened by previous passage over the curve will eventually crack.  Lubrication may need thinking about as well; models are supplied new with a silicone grease that can harden over time and become the very opposite of lubrication, and if it is replaced with a mineral oil based product, chemical reaction can make the nylon the gears are made out of brittle and prone to cracking; use a non-mineral oil based product, sparingly.

 

Why do manufacturers not use more reliable brass or tungsten gears?  Cost (and maximising profit), obviously, but also because nylon has a small amount of 'give' in it which, unless the system is abused in the ways described above, enables closer meshing and more efficiency from the motor, especially when running slowly with DC, when the current is at it's lowest; it is a part of the smooth running we have come to expect from RTR mechanisms these days.  Modern motors are low current consumers, which is necessary for DCC operation.

A whole load of misinformation there!

 

But lets just concentrate on the suggestion that 'it's all the fault of the owner'.

 

There is a whole thread of 'Mazak Rot' for starters where owners models have become completely unusable, even where the models haven't left their boxes. No something is seriously wrong with the way stuff is made these days.

 

In the day, Tri-ang and its later renamings, made their stuff locally and if problems such poor quality castings, they could easily make replacements very quickly.

Now if the 'manufacturers' find a problem, they have to 'buy' a time slot in the production schedule, from Chinese factories. Sometimes it can take years for such slots to occur.

 

Plastics can be very dodgy and crack/split making item like gears and similar next to useless, which of course puts a loco effectively out of action.

I suspect the underlying cause is recycled plastic, which is probably very difficult to quality control. I'm not an engineer/chemist, so I can't prove any such theory, but it seems entirely logical to me.

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There's an old engineering dodge which can improve the grip of gears onto a shaft or axle. You will need a narrow, coarse file and a hard surface to roll the shaft or axle along. Any wheels on the axle will have to be removed. Put the axle on the hard surface, place the file on the area where the gear will fit, press down on the file and use it roll the axle to and fro a few times. Job done. In effect you create a knurled surface, though it won't look like a proper machined one, with a slight raising of the surface where the file has been.

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The problem is basically that plastic is an unsuitable medium for making gears (and wheels!), especially if they are force fitted to the shaft* or an incorrect lubricant has been used. Once split, the teeth no longer mesh correctly. Luckily most model gears are fitted to 2mm and have a 0.5mm  module and replacements are available from the Far East.

 

*Tolerances will ensure that at least some are too tight.

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Ive had split gears on Hornby 56s, substandard plastic.........no incorrect plastic type, maybe, incorrect design....possibly....

 

substandard implies that the chemical makeup of the plastic is incorrect for the type we dont know that to be the case, plastic however does age with time, and oils and solvents will speed this up, but also dont forget that the designs of gears over the years hasn't changed but the weight of the locomotives and In a lot of cases the weight we are pulling behind them has gone up and up and up...which puts more stress on them and will inevitably they will fail more often. Johnster does touch on this....

 

Ive never had a drive shaft fail but ive had the drive cups come away from he shaft (which I think the OP might be refferring to) this I think is incorrect design on the manufacturers part and the only thing I can link it to is not taking into account shaft expansion as the motor warms up.

 

 

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7 minutes ago, pheaton said:

Ive had split gears on Hornby 56s, substandard plastic.........no incorrect plastic type, maybe, incorrect design....possibly....

 

substandard implies that the chemical makeup of the plastic is incorrect for the type we dont know that to be the case, plastic however does age with time, and oils and solvents will speed this up, but also dont forget that the designs of gears over the years hasn't changed but the weight of the locomotives and In a lot of cases the weight we are pulling behind them has gone up and up and up...which puts more stress on them and will inevitably they will fail more often. Johnster does touch on this....

 

Ive never had a drive shaft fail but ive had the drive cups come away from he shaft (which I think the OP might be refferring to) this I think is incorrect design on the manufacturers part and the only thing I can link it to is not taking into account shaft expansion as the motor warms up.

 

 


there appears to be assumptions that this issue has arisen from use. This particular loco and all the others I have found are brand new from the box. The only thing is some I have had around two years some others Are older. The Cardon bearings have nice splits in both of them and have not just come away

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Where are you storing your models?

 

I once left a Farish tank engine in a car for a week in early spring with near freezing temperatures at night and warm sun during the day. The end result was a split gear on a previously well running model. Sheds & lofts might feel similar temperature swings.

 

Steven B.

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2 hours ago, Andymsa said:


there appears to be assumptions that this issue has arisen from use. This particular loco and all the others I have found are brand new from the box. The only thing is some I have had around two years some others Are older. The Cardon bearings have nice splits in both of them and have not just come away

in my case the class 56 issue it is from use.

 

the drive cup issue, ive seen (predominantly on Heljan models) has been from new.......but it became an issue, when the cracks caused the drive cups to slip on the shaft.

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1 hour ago, Steven B said:

Where are you storing your models?

 

I once left a Farish tank engine in a car for a week in early spring with near freezing temperatures at night and warm sun during the day. The end result was a split gear on a previously well running model. Sheds & lofts might feel similar temperature swings.

 

Steven B.


either they are stored in the house at room temp or in my railway building which has air conditioning so maintains constant temperature 

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14 minutes ago, pheaton said:

in my case the class 56 issue it is from use.

 

the drive cup issue, ive seen (predominantly on Heljan models) has been from new.......but it became an issue, when the cracks caused the drive cups to slip on the shaft.


that’s exactly the issue I have slipping due to split cardon bearings

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Probably a mis match between the spec of the  plastic specified by the procurer/importer and the cheaper plastic used by the manufacturer.   I haven't found any split plastic gears on my  50 year old  Triang power bogies or on Lima locos, worn out yea.  Split no.   Using the right spec plastic would help as would having the designers and the production line in the same building.

In the short term Brass replacements sound like the answer if anyone has the production capacity or the individual modeller has a lathe.

 

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I've had several Proto 2000 US outline locos with split axle gears, recognisable by a clicking noise when running.  Most of them have had very little use but I understand it is a common fault.  I found the best way to to rectify the situation was to buy a bag of Athearn axles (complete with wheels and gears) and use them to replace the originals.  I bought these from Model Junction when they were in Slough but I understand they have now (or soon will be) closed.

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It doesn’t have to be “the wrong kind of plastic” in order to fail if the mechanical design isn’t quite right ...... The plastic gear grips the steel shaft by hoop-stress, and if that stress is too great, too big a shaft, or too small a hole, whichever way you look at it, the gear, being the weaker material, will give at its weakest point, just like an over-stretched elastic band, which is exactly what it is. My suspicion is that designers routinely got this wrong until they’d built-up experience of designing for ‘non-keyed’ fixings.
 

None of which helps fix the blighters, which is annoying, ‘cos I’ve got a 16mm/ft ‘diesel’ out of service for exactly this reason.

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I have a Bachmann F9* with a split idler gear to one axle of the powered bogie. I thought, "I'll just disconnect the axle without the traction tyres and she will still go. So she does, but now suffers from an inability to pull anything!   :scratchhead:

*Bachmann call the model an F9, but it looks like an F7 to me.  (?) (Not that I claim to be an expert in the myriad variations of the EMD F series.)

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