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Wheel-rail interface including back-to-backs

Posted: Sun Oct 07, 2018 10:51 pm
by Caiptean
Forum members may be interested in the following on the importance of the wheel-rail interface including back-to-backs. :)

Re: Wheel-rail interface including back-to-backs

Posted: Mon Oct 08, 2018 12:11 am
by Mountain Goat
The gentleman (From what he relates to via the stock he runs) uses finescale track. Now he does mention the wheel profile. There is a little more to it as if any of you have tried them on ordinary code 100 00 gauge track, nothing seems to run as well as a metal wheeled Lima coach or a silver seal wheeled Hornby coach (If they dont have wheel wobble. The round axled silverseal wheels are less prone to issues) if the code 100 track has the flange ways of a suitable depth and tolerance to accept them. Why? Because the wheel profiles get to work on thew corners. The sideways play is necessary to allow the wheel profile to do its work. Little play means the curved profile can't tilt the coaches inwards at the corners and therefore doesn't get to do much.
It is interesting how things have changed. True, today's metal wheels keep lovely standards where it is rare to get wheel wobble. One does however still get poor wheel profile causing issues, and of course, the back to back issue.
Today's pointwork, even in code 100 is less tolerant to older wheels as they try to cater for modern finer wheels. Now flange depth does matter for two reasons. Too deep and ones wheel will ground on the bottom of the flangeways causing the wheels to jump when they hit frogs. Too shallow and they can't cater for any misalignment at the track joins. Any slightly larger gap between the joints or anything which may need a more sudden direction change will be less likely to stay on the rails if there is not sufficient flange depth to hold the wheels on the rails. Its a bit of compromise between too much or too little.
While I say nothing runs as well as the old Lima coaches with metal wheels (00 gauge), if one doesn't have track which is built to cater for them (Finescale track does not) then they won't run well, and likewize, modern finescale stock built for finescale track may not like running on non finescale track.
Here is where the horses for courses comes into play. Why dont we all adopt finescale wheels and finescale track? Well, we can if we want to. But why were models made with deeper flanges and a more pronounced profile in the first place, not to mention more play for the profile to do its job?
Well consider this. The older standards were made so that layouts could fit in a small space. The first radius curves were (And still are) a Godsend to many who simply dont have the space to use larger radius curves. Now with finescale wheels and curves, they really need second radius as a minimum to be happy. They will run on tighter curves if the design of the loco or rolling stock allows them to, but try running them at speed! Yet older stock with their more generous allowances will run at speed round sharp curves.
That's why I say horses for courses.

Plastic wheels. We all prefer metal wheels so why were plastic wheels so popular? Well, years ago in 00 gauge the majority of modellers who could afford them ran Hornby Dublo 3 rail. These were all metal regarding their wheels so didn't need isolating from one wheel to another. However, with the push to adopt 2 rail, plastic wheels were one of the main solutions to keep one wheel isolated from the other. They became so popular that for years plastic became the main material used with rolling stock despite their issues. Some say that plastic wheels are prone to attracting the dirt but to be fair, the dirt comes from dirty track. Plastic wheels are more likely to pick up this dirt from the track while metal wheels are more likely to leave the dirt on the track rather then pick it up. The dirt still needs dealing with be it on wheels or be it on track as if it is not on plastic wheels it will be preventing the locos from running...
Here is the larger issue with plastic wheels. Untrue wheels. Just like metal wheels being good or bad depending on their quality, plastic also varies. I've seen some very good true running finescale plastic wheels and I've seen others which even puzzles me how the things stayed on the track!
Generally metal wheels are better for their nice rolling weight and their metal pin point axles. Better quality plastic wheels mostly have metal axles but they are normally lighter in weight. The weight does make a difference. Metal Lima wheels run well (On siutable track) because they have good rolling weight (If one isn't taking account of other aspects). Romford wheels are lovely and heavy (The disc and 3 hole disc wheels. Spoked less so) and are finescale with lovely profile mixed in and run well both on finescale and non finescale layouts. Is a shame Romford dont still make wheels as they used to be a good price as well.

Re: Wheel-rail interface including back-to-backs

Posted: Mon Oct 08, 2018 12:29 pm
by Caiptean
From regular questions raised on the Hornby forum it became clear that there was a lack of basic understanding in respect of the whee-rail interface; particularly the importance of correct back-to-back settings.

Accordingly the guide was written to give modellers a simple overview of the importance of the wheel-rail interface, albeit from the perspective of modern code 75 /code 83 /finescale track and the wheel standards (primarily back-to-back) that apply. Although also applicable to modern code 100, it was not intended to cover the coarse wheelsets of days past (which as standards improve increasing relate to collector's models).

Back-to-back settings are particularly important in respect of model railway's common crossings (from the perspective of a professional railwayman in the UK the USA term 'frog' relates to toy trainsets /green amphibians /switches in trolleybus overhead wiring). Finer scales of trackwork (even code 100) may not cope with older coarse wheels which typically suffer from excessive flange depth and flange thickness - replacement with finer wheels often being required.

In respect of defined wheel profiles these vary amongst manufacturers; in any event model railway tracks do not normally use inclined rails. Standards for wheel profiles are covered in the links given under 'further reading'.

I trust this clarifies. :)

As an side some railways (such as the Glasgow underground) use flange-running through its common crossings.... :D

Re: Wheel-rail interface including back-to-backs

Posted: Mon Oct 08, 2018 1:00 pm
by Brian
A lot of information can be found on UK OO standards on the Double O Gauge Associations web site... Intermediate measurements are the UK standards for Hornby/Bachmann/Dapol/Heljan etc and Hornby & Peco track systems

Re: Wheel-rail interface including back-to-backs

Posted: Mon Oct 08, 2018 3:28 pm
by Caiptean

A useful reminder of the DOGA standards which have now been added to the webpage.

Kind regards,

As an aside DOGA was originally set up by modelling friends of mine but at the time its constitution meant they could potentially derive an income from the membership; something I was not comfortable with. So I deliberately didn't too get involved following its formal startup. ;)