A Weighty Question

[Matthew W]

I don't remember ever seeing a discussion of how heavy 2mm rolling stock should be. It is common ground that for locos "the heavier the better". But what about rolling stock ?  I am thinking of drafting a piece for the 2mm Association Finescale Manual about this, and would welcome other peoples thoughts and experiences. To start the ball rolling:

 

1. Farish and Dapol bogie carriages with finescale wheels seem to weigh about the 20g mark, ie an axle loading of 5g. From seeing them in action that seems to be light enough to allow long trains to be run but sufficient to keep them on the rails. I imagine the same would go for modern bogie wagons -is that so ? Or do people run heavier coaches/bogie vehicles ?

 

2. I have never made a brass kit coach - what, typically would one weigh ? Anecdotally, it seems there is a concern that all-brass coaches can prove too heavy for long trains, but is this true ? If so, how much can be saved by ( for example ) using lighter materials such as plastic or wood ( for example, for roofs or interiors ) ? 

 

3. How heavy do steam age 4-wheel wagons need to be ? I have a collection which weigh between 4g and 6g ( an axle loading of 2-3g ) and that seems enough to keep them on the rails. Is there an "ideal" weight ? 

 

4. On the other hand, is more weight needed to allow couplings to function properly ? There is a degree of "stiction" in DG or B&B couplings and arguably wagons need to be heavier to allow these couplings to work properly for shunting purposes. Is this also true of other couplings like the Electra ? 

 

5.  Is there such a thing as too much weight ? I have a bogie tank wagon which weighs 27g ( an axle loading of nearly 7g ) and it is little used because of the disproportionate drag it creates in a train. 

 

6. I have never made a brass wagon kit, partly because of concerns about the resultant weight. What typically do they weigh ? And what are other peoples' experiences ? 

 

7. Has anyone tried making a brake van heavier to impose some drag and keep couplings tight ? Or does this just cause derailments ?

 

Any thoughts or evidence gratefully received !

 

Matthew 

[Chris Higgs]

You might want to consider this reference: https://www.nmra.org/sites/default/files/standards/sandrp/pdf/rp-20.1.pdf

It only takes into consideration bogie stock, I wonder when exactly American railroads last had any 4-wheel stock.

 

Many people have observed an all brass coach does weigh a lot, probably too much. Interiors made of lighter materials, and perhaps open spaces in the floor could help to reduce this.  I also know Colin Allbright felt that the resin roofs in my kits might present some stability issues with a high Centre of Gravity.

 

On point 7 I do recall managing to pull complete trains off the track on tight curves. It was Hornby Dublo 3 rail, mind. I think consistent weight throughout a train is a jolly good idea.

 

Chris

Edited March 22, 2023 by Chris Higgs

[richbrummitt]

17 minutes ago, Chris Higgs said:

 

On point 7 I do recall managing to pull complete trains off the track on tight curves. It was Hornby Dublo 3 rail, mind. I think consistent weight throughout a train is a jolly good idea.

Easy to do with Brio and other children’s toys (where the trains are much longer than the curves they are travelling along) as well.

I have played with making brake vans heavier or ‘sticky’. It helps to avoid wagons hunting but too much weight and maximum train length is impacted as you alluded to in your point 5. 

[Matthew W]

Thanks both. Applying the NMRS formula to a typical US 40 foot boxcar gives an optimum weight of 18.5g ( an axle loading of about 4.6g ).

 

I took a random selection of three N gauge US boxcars from different manufacturers and out of the box they weighed respectively 17, 24, and 31g. In true Goldilocks style, the first felt "a bit light", the last "too heavy", and the middle one felt "about right". 

 

I then tried a Farish bogie bolster. Out of the box, with Farish wheels thinned down to 2mm, it weighed a meagre 8g, but runs well enough. Adding 11g ( which brought it to close to the NMRA "optimum weight" ) if felt " a bit too heavy" - it was noticeably less free running.

 

Then I tried two UK 4-wheel vans coupled together, total weight 17g on four axles so theoretically close to the NMRA standard. They run noticeably less freely than the bogie bolster, no doubt because the two chassis do not castor as well as a true bogie vehicle ( Gosh ! bogie vehicles are better runners than four wheelers - who would have guessed ?!! ).

 

Does this tell us anything useful ? The NMRA point out that too much weight is disadvantageous, which seems right, and my feeling is that the NMRA optimum is unnecessarily heavy for British 2mm models. I suspect that you need a minimum of about 2-3g per axle and a bit more might be better, up to about 5g per axle - but that is not a "scientific finding" ! 

 

Matthew

 

 

 

 

 

 

[Nigelcliffe]

A few random weights from my collection

 

Short LNER non-corridor bogie coach (Chris Higgs etch ) 37.5g     

 

Etched steel coal hopper (either Association or Bob Jones ) 8.7g

 

CCT 4 wheeled coach (Association) 19.9g

 

4 wheel steep plate wagon (Stephen Harris ) 8.8g

 

4 wheel 10ft w/b van (Association plastic body, Association underframe) 5.8g

 

4 wheel cement hopper (Stephen Harris )  10.8g

 

4 wheel open wagon (Association plastic, association underframe) 4.6g

 

4 wheel outside framed van (etched, probably Chris Higgs ) 10g

 

 

So, those have a range of 2.3g to 10g per axle.    
The 2.3g stuff is very light, and I think needs ballast adding.  the 10g stuff is heavy and possibly causes haulage issues in longer trains.  

 

 

- Nigel

[Chris Higgs]

Personally I think there isn't going to be one answer to this anyway. If you have a small shunting plank/branch terminus layout, I'd put plenty of weight in. I have seen a few 2mm/N layouts where the light stock barely seemed to hold the track, and gave no impression whatever of the mass of the real thing.

 

Whereas if you want long trains, obviously you do need your locos to be actually able to pull the stuff.

 

Chris  

[yaxxbarl]

On the level I think the greatest need when starting a train is to overcome inertia and bearing-related friction, to which free running is the best contribution whatever the mass of the vehicle is. Once a train is moving and it gains momentum then a bit of mass to impart that momentum definitely helps.

 

In my experience, the best free running comes from the standard metal axle and brass top hat bearings combo of most rolling stock made up from association kits.

 

Converted rolling stock, such as adapted N Gauge stock with replacement wheels, generally has metal axles into plastic bearings. Depending on the quality of the bearing and the closeness of fit this can also be quite smooth running.

 

On gradients, that is where the mass of the vehicles comes more into play as as well any inherent friction in the bearings as the hand of gravity comes in - my converted 4F will happily handle 30 wagons on the flat, add a gradient in and it starts slipping. The cure (certainly on my test circuit) is to have a 3F Jinty banking it from the back!

 

John.

 

 

[queensquare]

After discussions over on my Bath thread I weighed some of my coaches. As Nigel found , etched coaches averaged out at around the 37g mark whereas Farish Mk1s were around 24g. A rough calculation suggested that six brass coaches equates to nine plastic RTR. 
 

Jerry 

[garethashenden]

My personal take is that the NMRA standards are a little heavy handed. The current standard is 33 years old and a lot has changed in American N since then. Free running metal wheels were unheard of then, and they're very common now. Etched 2mm underframes with their brass bearings roll even more easily than the best new US boxcars. Adding weight can help mask problems, but there are often better solutions. Poorly laid trackwork, too tight curves, misaligned couplers, jerky mechanisms, can all be smoothed by more weight, but they're not cured. A consistent weight is good, but it doesn't need to be that heavy. Two big issues with train handling are heavy next to light and long next to short. You can run a long train of 16T minerals and they'll be fine, because they're all the same length and weight. Their actual weight doesn't matter. The opposite example is American centerbeam flatcars. They're long, light, and have a high center of gravity. As a result they fall over on the inside of curves all the time. 

 

Consistency is key. Find a target weight that you can bring everything to and do that. But it doesn't have to be to NMRA specs.

[Matthew W]

Thank you to everyone - I think I have enough to put something sensible together.

 

Matthew