Wheel back-to-back standards

[Joseph_Pestell]

This may not seem like a track design question. But bear with me: I have had a sleepless night and had a "big idea". Apologies if someone else's grandma has already sucked this particular egg.

 

As many of you will know, I have been looking into producing "00" ready-to-lay track and turnouts. I have put "00" in quotes because one of the questionmarks is whether it would not be better to make it 16.2mm gauge. I don't want another long thread about the various merits and demerits of this approach but it does allow standard modern steam-outline models to run better through pointwork and for that pointwork to look much better through having reduced flangeways. The reason for that is that nominally 16.5mm gauge locos have narrow back-to-back dimensions to allow them to run round "trainset" curves. The downside is that reducing the track gauge to 16.2mm is that curves have to be wider which many modellers do not have the space for.

 

Now I may have missed something (often do!) but so far as I know all the various 4mm track standards each specify only one back-to-back measurement. And the advice to modellers suffering derailment problems is always to check for consistent back-to-back. But is that not WRONG?

 

Our constraining factor in determining curve radius is the long fixed wheelbase of a steam loco or the bogies on certain diesels (1CoCo1). But while this sets the flangeways for pointwork, there is no reason why short wheelbase wagons and coach bogies (and some diesel locos) could not have a wider b-t-b than locos.

 

This does not give the aesthetic gain of narrower flangeways but should improve running, particularly when shunting a long train of short wheelbase wagons in reverse.

[bertiedog]

First forget scales, it is gauges we deal with and 16.5mm works perfectly if the correct wheels are used, The NMRA sorted this out 60+ years ago in the States, and it is perfectly valid for 16.5 here in the UK. It is an engineering problem, nothing more.

 

4mm scale makes not a jot of difference. The Problem is manufacturers that still are plain ignorant, obstructive or wantonly protective of their ideas to bother to make things to a standard.

 

16.2 works by accepting the appalling bad interpretation of wheels standards, it tinkers with the track, and does have an effect in using the width of the tyre to prevent the wheel dropping into the frog gap.

 

We have a bad track for 4mm already. making it worst again is not a cure, despite the smaller flangeways improving "appearance".

 

There are few who would commercially buy track or points in it, but 16.2 mm suits PC assembly 100% already, so where's any market for making such a product.

 

A better approach would be the adoption of a British standard for 16.5mm, from a British MRC wiith national status,and putting a rocket under the feet of makers who do not make wheels to standards.

 

If it is vital to run assorted types of wheels on one track, then 16.2 is the one for you, but remember it is a new product and further dilutes the already wide choice out there, better would be the support an effort going into improvements not compromise..

 

Stephen.

[bertiedog]

The wider Back to Back on stock will cause issue with most commercial points, with the flange allowing the tyre to hit the nose of the frog, at least in theory. A lot depends on the height and thickness of the flange and whether a correct rounded tip or a pizza cutter. Peco try to allow for the various wheels as much as possible, but have you seen proper RP25 standard wheels on Peco Code 83, it is a joy to watch, smooth transition over the points. If they adopted a UK version, half the makers rubbish wheels would not go through, let alone smoothly. Code 75 works, but only if you are strict with your self and buy in only wheels to a tight standard. Unsprung stock works better with code 75, fully sprung "can find the gap", and judder a bit as the frog is crossed.

The whole issue is horribly complex to explain in simple terms, a trap for the unwary, but it can be sorted by better wheels.

 

Stephen.

[DCB]

I simply don't understand the rationale of 16.2 mm gauge, why not narrow the flangeways on 16.5 mm? Most people run 16.5 mm on straights and something less on curves as flexi almost invariably goes tight to gauge when curved unless you cut the sleeper base between every sleeper on one side.  

 

In my experience manufacturers back to back can vary quite widely, the old Hornby Dublo wheels were consistent but slightly under 14.5, I make it 14.2 sliding fit so as they run nicely through code 100 and code 75 points I standardise on 14.2 with home made back to back gauges.

[bertiedog]

I simply don't understand the rationale of 16.2 mm gauge, why not narrow the flangeways on 16.5 mm? Most people run 16.5 mm on straights and something less on curves as flexi almost invariably goes tight to gauge when curved unless you cut the sleeper base between every sleeper on one side.  

 

In my experience manufacturers back to back can vary quite widely, the old Hornby Dublo wheels were consistent but slightly under 14.5, I make it 14.2 sliding fit so as they run nicely through code 100 and code 75 points I standardise on 14.2 with home made back to back gauges.

16.2 allows wayward manufacturers wheels to run on the track and points. It does make running better, but it is a poor solution to keeping makes on their toes and sticking to a standard that already works. The point, if you like, is in the points, the wheels are restricted to a path where in theory, the outer edge of the wheel tyre does not fall into the gap, as the outer edge is running on the other rail alongside the frog.

This stops the wheel drop that most 16.5mm points suffers from.

Better in the longer term would be the adoption of UK standards based on the proven NMRA ones.

Stephen

[mightbe]

I simply don't understand the rationale of 16.2 mm gauge, why not narrow the flangeways on 16.5 mm? Most people run 16.5 mm on straights and something less on curves as flexi almost invariably goes tight to gauge when curved unless you cut the sleeper base between every sleeper on one side.  

 

The downside is that reducing the track gauge to 16.2mm is that curves have to be wider which many modellers do not have the space for.

 

Track gauge is expressed in terms of a minimum value only, for the simple reason that flanges are in between the rails. Track gauge can be freely widened without issue, but never narrowed. There is no incompatibility between 16.2 mm and Peco--they require the same back to back and use the same checkspan. If you want to make 16.5 mm the sacrosanct dimension while still narrowing the flangeways, you arrive at a standard that is 100% incompatible with the other two (and all RTR rolling stock). Effectively you'd have DOGA-Fine.

 

Curves, using 16.2 mm nominal gauge, can be the same as standard 00 when you take gauge widening into account. Simply use standard 16.5 mm flextrack. There is no inherent contradiction between 16.2 mm nominal gauge and 22" curves.

 

If you take 16.5 mm as the nominal gauge with 1 mm flangeways, you can't use 16.5 mm flextrack through tight curves. You would need something like 16.8 mm. Or build it yourself. 

 

16.2 mm nominal gauge would be the 'easy route' 

 

Quentin

[Dungrange]

Now I may have missed something (often do!) but so far as I know all the various 4mm track standards each specify only one back-to-back measurement. And the advice to modellers suffering derailment problems is always to check for consistent back-to-back. But is that not WRONG?

 

Our constraining factor in determining curve radius is the long fixed wheelbase of a steam loco or the bogies on certain diesels (1CoCo1). But while this sets the flangeways for pointwork, there is no reason why short wheelbase wagons and coach bogies (and some diesel locos) could not have a wider b-t-b than locos.

 

I think that you are mixing up two separate issues here.  The back-to-back measurement through point work is determined only with reference to a single axle.  It needs to be set at consistent distance to avoid the flange hitting the crossing V.

 

The length of the fixed wheelbase should have no impact on the back-to-back dimension, but does impact on the amount of gauge widening that has to be applied to curved track.  The longer the wheelbase of any item of rolling stock, the more gauge widening is going to be required.

 

The 16.2 mm track gauge is perfectly adequate for shorter wheelbase rolling stock, even on tighter curves, but as wheelbase increases, so too does the minimum radius to which you can lay track without widening the track gauge towards 16.5 mm. 

[Joseph_Pestell]

I think you guys are missing the point that I am trying to raise.

 

Locos have a back-to-back which is narrower than it ought to be for 16.5mm so that they can get round curves.

 

Wagons and bogies, being shorter, don't need that slop in the dimensions. So, it seems to me, the b-t-b for wagons and coach bogies should be greater than that for locos. The reason that wagons (and pony wheels) are striking the point of the crossing is that they are not being held firmly in place by the rail due to an unnecessarily reduced b-t-b.

[DCB]

Still not with you Joseph.  The back to back between wheels should be large enough to allow both flanges on a single wheelset to pass through a pair of check rails and small enough to prevent one flange striking the crossing nose when the other is against the adjacent check rail.

 

Neither flange should contact the rail head except on very tight curves as the coning on the tyres should keep the wheel flanges away from the rail head.  

[mightbe]

Usually all wheelsets are set to the same back to back, regardless of fixed wheelbase. Sideplay on the middle axle(s) is the usual answer, on both kit/scratchbuilt and RTR. I don't think RTR makers (or anyone else for that matter) intentionally use different back-to-backs on locos. It may be down to tolerances and quality control

[Dungrange]

I think you guys are missing the point that I am trying to raise.

 

Locos have a back-to-back which is narrower than it ought to be for 16.5mm so that they can get round curves.

 

Wagons and bogies, being shorter, don't need that slop in the dimensions. So, it seems to me, the b-t-b for wagons and coach bogies should be greater than that for locos. The reason that wagons (and pony wheels) are striking the point of the crossing is that they are not being held firmly in place by the rail due to an unnecessarily reduced b-t-b.

 

Okay, I think I get the point that you are trying to make and you are correct in relation to plain track.  That is, the 00 track gauge is narrower than the scale dimension and the back-to-back of commercial ready to run stock is even further from prototype dimensions than the track gauge.  The reason for this is that to negotiate train set radius curves, there needs to be quite a bit of 'slop' to allow stock to negotiate curves that are much much sharper than prototype curves.  The longer the wheelbase the more 'slop' is required and conversely, the shorter the wheelbase the greater the back-to-back dimension could be.  If your layout were an oval of plain track with no point work, then I suspect you may be able to obtain better running with a larger back-to-back dimension on the shorter wheelbase stock.

 

However, varying the back-to-back dimension is not a good idea in relation to point work as it would in many instances make the check rail redundant.  The purpose of the check rail is to ensure that the opposite wheel does not strike the V and therefore in order to function correctly, the wheel and track standards need to be compatible and since the distance between the check rail and the opposite rail is fixed (and therefore constant for all stock that passes through it), the back-to-back of all stock should be similarly consistent.  That is, the back-to-back is not determined from the radius of curves or the wheelbase of stock, but solely to be compatible with the chosen distance between check rail and the opposite rail.  As you increase that distance, you need to increase the back-to-back distance to maintain the same running standards. 

[Izzy]

I think you guys are missing the point that I am trying to raise.

 

Locos have a back-to-back which is narrower than it ought to be for 16.5mm so that they can get round curves.

 

Wagons and bogies, being shorter, don't need that slop in the dimensions. So, it seems to me, the b-t-b for wagons and coach bogies should be greater than that for locos. The reason that wagons (and pony wheels) are striking the point of the crossing is that they are not being held firmly in place by the rail due to an unnecessarily reduced b-t-b.

I understand the point being made.There is nothing to stop you having differing b-t-b measurements, lets face it for many years most RTR has. This of course leads to the need for 'universal' points that can accept the variations............and the running quality that results. I think that this has been discussed on the odd occasion..........

 

Izzy

[DCB]

I think you need to stick with one back to back plus or minus 0.25mm and one flange profile, RP 25 or NMRA.

 

With overscale flangeways the minimum radius points to keep the tread supported across the gap is going to be huge, maybe 24foot radius and may not be achievable in practice.  I would look seriously at a shallow flangeway which supports the flange over the gap a la H/D 3 rail as a smooth running solution.  You can push 20 odd H/D wagons over 15" pointwork reliably so their way works.   I can't use a shallow flangeway as I have some very old deep flanged wheels in use, including a mid 1960s Triang Britannia, but in an ideal world I would standardise on Hornby Dublo wheel profiles and back to back simply because I get so many fewer derailments than with shallower sharper flanges.

 

Oddly enough you don't necessarily need a constant Back to Back Triang wheels from the late 1950, and even 1970s Hornby Sir Dinadan Tender wheels were in two halves which slid on the axle and the B to B varied between about 13.5mm to 15mm  They run nicely through Peco code 100 points if you insert a small (8ba?) washer between the halves but wont run nicely through Hornby Dublo points as the flanges are too deep.    

[Joseph_Pestell]

May be need to do a bit of experimentation.

 

I take the point that having a wider b-t-b on wagons will impact on the effectiveness of the check rails. That might cause an issue on small radius pointwork but I think might work OK on larger radii.

[Nearholmer]

If the "b-t-b + flange thickness" is too large for the check-rail setting, then the flange can hit the crossing nose, irrespective of the radius of the turnout. On tight turnouts it will happen nearly every time; on shallow ones you might get lucky, and only have it happen some of the time, but when it doesn't happen, it will be by luck, not judgement.

 

As has been said here, and many places elsewhere, the track and wheel-sets have to form a set of compatible parts, in order to work properly. What they don't have to be is exactly (or even very close) to scale replicas of real ones; they just have to be compatible.

 

I run indoors using Coarse 0, and outdoors using LGB track and wheels. Neither bears very much resemblance to scale, but both run very well, because the wheel-sets and points are compatible. I used to model in H0, and was a massive fan of NMRA standards, which are properly designed to yield compatibility - their RP25 wheel profile looks pretty good too, being "fine enough" to my eyes.

 

So, if you don't want to invent a whole new set of compatible standards (a hobby in itself), then "the path of least pain" in 16.5mm scale is probably to use Peco points and fit your stock with wheels that are properly compatible with them (NMRA RP25 certainly are with Peco Code 83 FB).

 

Kevin

[kevinlms]

.  If your layout were an oval of plain track with no point work, then I suspect you may be able to obtain better running with a larger back-to-back dimension on the shorter wheelbase stock.

I suppose you could test the theory by building a model of the Glasgow Underground, in its original form. That consisted of an inner & outer loop without any point work.

[Nearholmer]

Another option is to use truly universal points (not what Peco call universal), which will accept any wheel-set within the bounds of reason, and provide complete support through the crossing.

 

Only trouble is, nobody has made them commercially in 00 for about fifty years!

 

Collectors of ancient model trains will scour the earth for Wrenn Universal points, because they allow all makes to be run on one layout.

 

Kevin

[Joseph_Pestell]

Another option is to use truly universal points (not what Peco call universal), which will accept any wheel-set within the bounds of reason, and provide complete support through the crossing.

 

Only trouble is, nobody has made them commercially in 00 for about fifty years!

 

Collectors of ancient model trains will scour the earth for Wrenn Universal points, because they allow all makes to be run on one layout.

 

Kevin

Would modern wheelsets really run OK on this?

[Nearholmer]

Yes, without the slightest difficulty.

 

The "trick" is that, rather than just the switch-rails moving, and the check-rail guiding the wheels past the crossing nose and wing-rail, the entire switch-rail and wing-rail assembly pivots, so that there is no gap at all at the crossing nose, and the check-rails do nothing at all; they are purely cosmetic, and are set with wide clearance to accommodate wide flanges and narrow b-t-b.

 

Points of this kind have a very respectable history: all traditional tinplate points operate on a similar principal (the detail is slightly different); and, John Ahern used them on The Madder Valley, because he too was plagued by variable wheel standards from indisciplined manufacturers. THe 00/H0 wheel standards problem dates back to at least the 1920s, and people seem to have forgotten this particular dodge to get around it.

 

These truly universal points don't, of course, work like most real points (there are some real ones that are somewhat similar, known as "swing nose crossings"), but they do work, with a huge variety of wheel-sets, and running through them is,mfo course,super-smooth, because there is no gap to cause "frog drop".

 

Hope this is helpful.

 

Kevin

 

BTW, they are easy to scratch-build too!

[kevinlms]

Another option is to use truly universal points (not what Peco call universal), which will accept any wheel-set within the bounds of reason, and provide complete support through the crossing.

 

Only trouble is, nobody has made them commercially in 00 for about fifty years!

 

Collectors of ancient model trains will scour the earth for Wrenn Universal points, because they allow all makes to be run on one layout.

 

Kevin

But the use of rubber bands, isn't such a good idea!

[Nearholmer]

Not in the long term, it would appear.

 

K