7mm Wheel Standards

[BG John]

I went EM back in the early Protofour days when Studiolith were about the only supplier, and it seemed too difficult for a 16 year old. Now I'm starting in O gauge, it seems to me that finescale is pretty much the 7mm equivalent of EM, so I'm happy to use it. I'm even OK about moving 0.5mm further away from the correct gauge to use O-MF, as it still feels close enough, and a reasonable compromise.

 

Where I did change to P4 standards though, was for modelling the broad gauge, where the narrower wheels with smaller flanges make it far easier to work with the features of broad gauge locos and rolling stock, and there's nothing RTR and virtually no mainstream kits available anyway. I think most 7mm broad gauge modellers use S7 standards, largely for the same reason, so if I ever do 7mm broad gauge I'll use S7. For narrow (AKA standard) gauge I might use S7 for obscure prototypes with little commercial support, but life's too short to convert every kit or RTR item I buy.

[Jeff Smith]

The case for P4 is somewhat different to the case for S7. P4 is a wheel and track standard that is visually very different from OO, which is where most people move from, so the jump from OO has considerable visual appeal for track as well as wheels. I'm guessing that the S7/7mm finescale debate is more akin to the EM/P4 debate - two standards that bear some resemblance to each other but are mutually incompatible.

[BG John]

The case for P4 is somewhat different to the case for S7. P4 is a wheel and track standard that is visually very different from OO, which is where most people move from, so the jump from OO has considerable visual appeal for track as well as wheels. I'm guessing that the S7/7mm finescale debate is more akin to the EM/P4 debate - two standards that bear some resemblance to each other but are mutually incompatible.

Which I think is kind of the point that I was making, that mainstream O gauge is pretty much equivalent to EM already. I imagine that few course scale O gauge modellers would aspire to S7, whereas a certain number of OO ones would aspire to P4.

[Jeff Smith]

John - our posts crossed in the post as it were.....great minds and all that......!

[Andy Reichert]

SNIP

 

This all goes to show that it is entirely possible for there to be a discussion about scale, gauge and standards without people falling out with each other, having a few jokes at each other's and our own expense, and with a healthy respect for other points of view.

 

Bet this discussion doesn't make the editorial pages of MRJ...

(No sausage related puns, you see.)

 

 

SNIP

 

As CJF worried, as there is no significant RTR support, and not everyone wants to build track, then as things stand, S7 etc are not for the majority, but I would argue that it has been the advocates of P4 and S7 who have done relatively more to push the envelope for better models than anyone else, and rather than throw prejudices about, we should simply accept the old adage that if we wanted to get to there, we wouldn't start from here, i.e. manufacturers would adopt finer track and wheel standards from the outset, to enable better models for all - maybe not S7, but closer to that, and in a way that more easily accommodated S7 standards.

 

I also remember Cyril criticising NMRA RP-25, on the basis that once a standard is defined, it is hard to change (improve) things. Not for the first time, he had a point, but possibly not without a degree of sef-contradiction.

The adoption, in the 70s, of the current G0G finescale standards by such as Slaters was a big step forward, but it was not made without some resistance from those with a large collection of models with coarser wheel and track standards. It also paved the way for the various standards involving narrowing of the gauge to 31.5, 31.2 and 31.00mm.

 

It would be a shame to see the inheritors of that evolutionary development of finer standards putting a stop to gradual future improvements in wheels and tracks.

 

SNIP

 

Good modelling requires consistency, regardless of wheel and track standards. The prototype offers good guidance on how to overcome some of he difficulties we face, based on two centures of overcoming them. It is a shame not to pay attention to it.

 

Ultimately, one sets ones standards and works to them, but the more informed that decision, the more aware one is of the consequences, and the more tolerant one can be of others' decisions in this area.

 

Simon

Edited for iPad-isms.

 

For an example of such above history repeating itself, see the recent topic of my  description of my own compromise 4 mm modelling standard, 00-P.

 

Andy

[Jeff Smith]

Simon,

 

Can you define 'better looking track'. How can 1.5mm under-gauge be better? Or are you referring to check-rail and frog gaps?

[jim.snowdon]

Simon,

 

Can you define 'better looking track'. How can 1.5mm under-gauge be better? Or are you referring to check-rail and frog gaps?

 i'll let Simon make his own response, but to my eye, the smaller flangeways are what is noticeable. The difference in the track gauge is not as it is proportionately much smaller and there are no instant giveaways (as there are with 00) of excessive sleeper length outside the gauge. I found the same was true in the smaller gauges, in that when I modelled in EM, on two layouts that made many appearances on the exhibition circuit, I got a fair number of comments to the effect of "was it P4". Again, it was the tight flangeways that were, I believe, the factor.

 

Jim

[BG John]

It's very handy that Peco code 100 OO turnouts have pretty much the same flangeways as O-MF, as it's helped me to avoid having to built my own on my new O/O-16.5 layout, and I can use OO gauge wheels and chassis for narrow gauge alongside O finescale!

[hartleymartin]

The O-MF gauge is basically reducing the gauge to 31.5mm, thereby reducing the width of the flangeway from 1.75mm to 1.5mm This has the effect of reducing the wheel-drop on the V-crossing of points and giving a finer appearance. The result being that the track remains compatible with standard, common-place GOG Fine Standard wheels.

 

It is also handy to model the track to a scale of about 1:45, as then everything looks in proportion with regards to the gauge, sleeper size and spacing. Sure, the cast chairs will be slightly over-scale, but this isn't really noticable, especially when you're in the habit of spiking down Code 100 or 125 flatbottom rail directly to the sleepers.

 

The 32mm gauge has a built-in slop-factor for curves where slight gauge-widening is desirable. Generally speaking, I'll widen the gauge to 32mm for curves, but bring it down to 31.5mm for points and straight track.

[Andy Reichert]

Writing from a proper track and wheel standard point of view:-

 

You don't try and reduce wheel drop at the crossing gap. It either shouldn't ever exist in the first place, or should be eliminated entirely by using the correct wheels for the standard, instead of for some reason attempting to use too narrow ones.

 

There is no such thing as wheel drop on a correctly dimensioned standard.

 

Andy

[Simond]

Better tell Network Rail....

 

Joking aside, and I'm sure there are people on here who can confirm or correct my view, I believe wheel drop (or "leap") must occur when the wheel traverses a properly constructed crossing, as the wheel tread is coned, and there is a relatively abrupt change in radius when the contact patch moves axially from the V to the wing rail (reducing radius - drop) or wing to V (increasing radius - "leap").

 

For this reason I understand that the blunt nose has a slightly reduced height at the end.

 

Views?

Simon

[jim.snowdon]

Simon,

 

Correct in one, and over the years engineers have played about with lowering the height of the crossing nose to prevent it being hammered, as well as ramping the top of the wing rails to match the coning of the wheel tread. Ny and large, none of it has provided a conclusive solution, as the crossing nose has to cope with a considerable variation in the shape of the wheel treads as they range from newly turned (now, to several different profiles) to fully worn, with or without a false flange due to the tread wearing hollow.

 

With the even narrower wheels used on traditional street tramways, even currently, wheel drop would be an even bigger problem, as a result of which they adopted the principle of raising the bottom of the flangeway through the crossing, so that the wheel was supported on its flange tip rather than the tread. OK at typical tram speeds, but not at railway speeds, as the wheel is lifted on entry to the crossing and dropped back again afterwards.

 

Jim

[Jeff Smith]

Jim - I thought riding on the flanges was strictly a model railway dodge. Of course it requires consistent height flanges.....

[Giles]

Henry Greenly was an extremely competent engineer in his area of the larger working passenger hauling locos. Even today, if you build a loco in 10 1/4" or above, using his formulae for grate area, valves etc., you'll get a good loco out of it. Of course it was prudent to go for a larger scale on a given gauge for very practical reasons - and that sometime still happens today! Greenly's book - 'Model Steam Locomotives', used with sense is still one of the most useful tomes out there for building large miniature locos.

 

It was only on his small stuff, where he believed coal firing wasn't viable, and LBSC proved otherwise that he got it wrong as was very well publicised at the time - but even LBSC had his moments.... 

 

Always worth a read if anyone comes across a copy!

[jim.snowdon]

Well, consistent within reasonable limits of wheel wear. It is not a problem if a newly turned wheel drops slightly, whilst a fully worn one lifts to the full height. There is no standard, but setting the flange depth at about 1/3 wheel wear would be a good compromise for a full size tramway. Of course, eventuually the bottom of the flangeway wears, but then on a tramway, you send for the welding team to build it back up again.

 

Jim

[Andy Reichert]

Better tell Network Rail....

 

Joking aside, and I'm sure there are people on here who can confirm or correct my view, I believe wheel drop (or "leap") must occur when the wheel traverses a properly constructed crossing, as the wheel tread is coned, and there is a relatively abrupt change in radius when the contact patch moves axially from the V to the wing rail (reducing radius - drop) or wing to V (increasing radius - "leap").

 

For this reason I understand that the blunt nose has a slightly reduced height at the end.

 

Views?

Simon

 

All of which applies to the large, heavy and often worn wheeled prototype, but is usually insignificant when applied to standards used in smaller scales modelling.

 

First model W&T standards usually specify wheels to be 10% wider than twice the flangeway width, so that wheel is still supported by the wing rail over the distance where the crossing vee point  might be prototypically blunted or sloped. So a properly blunted model vee should have absolutely no drop effect

 

Second the amount of UK prototype coning is 1:20. An “O scale fine” wheel is 3.75 mm wide, including its 1mm flange width. So the radius difference between inner and outer tread edges is only going to be 2.75/20 or 0.14 mm. That’s only a scale ¼” in O scale, which is going to be difficult to notice visually.

 

So rather than any model wheel drop due to coning , we are really talking just model wheel coning causing a “click”.

 

Andy

 

[jim.snowdon]

Andy,

 

The standard 0-F wheel is only 3.5mm wide, including the 0.75mm flange. That equates to a tread width of 2.75mm.

 

For Guild standard 32mm track, the flangeway is 1.75mm, and due to the mismatch between wheelset and track dimensions, the gap between the flange and the rail wheel can be as much as 1.3mm. With that combination of dimensions, the wheel can be unsupported through the crossing, hence the drop. Reducing the gauge so that it better fits the wheelset both reduces the lateral slop and the width of the flangeways, with the result that the wheel, now better guided through the crossing can be better supported through the wing rail to crossing nose transition. In our scale, it isn't about coning, although Simon's comment was in the context of full size wheels; for us in 7mm scale, it is about keeping the wheel supported at all through the croossing.

 

Jim

[robertc]

A prototype wheel on a railway is always more than twice the crossing flangeway gap such that no drop can occur if all is within tolerance. It is obvious that anyone with a sufficient amount of engineering knowledge would have realised the problem they were creating in the BRMSB standard when they decided to recommend a a reduced tyre width without a corresponding matching crossing gap for O-fine. Why the GOG did not correct it after their formation is beyond me. Congrats to the O-mf originators. Solves the issue yet retains the all important compatibility without which the 7mm hobby would not exist except for a few individuals working in isolation.

 

I chose Peco rather than hand laid for the outdoor layout this time around and had to modify the points to prevent wheels disappearing down the crossing gaps :>)  I have some stock that is still fitted with US 2-rail (supposedly) NMRA profile wheels and they run through smoothly (as they should) without mods to the points.

regards

 Bob

[Andy Reichert]

Andy,

 

The standard 0-F wheel is only 3.5mm wide, including the 0.75mm flange. That equates to a tread width of 2.75mm.

 

For Guild standard 32mm track, the flangeway is 1.75mm, and due to the mismatch between wheelset and track dimensions, the gap between the flange and the rail wheel can be as much as 1.3mm. With that combination of dimensions, the wheel can be unsupported through the crossing, hence the drop. Reducing the gauge so that it better fits the wheelset both reduces the lateral slop and the width of the flangeways, with the result that the wheel, now better guided through the crossing can be better supported through the wing rail to crossing nose transition. In our scale, it isn't about coning, although Simon's comment was in the context of full size wheels; for us in 7mm scale, it is about keeping the wheel supported at all through the croossing.

 

Jim

 

 

Diagram courtesy of the old NMRA web site.

 

I took the wheel data from http://www.walsallmodelindustries.co.uk/index.php/gauge_standards/?k=:2::

 

e.g.

Gauge ''0'' wheels are machined to BRMSB standards. The principal dimensions are as follows

 

width

tread width

flange depth

flange width

boss proud

Coarse scale

5mm

3.75mm

1.5mm

1.25mm

0.5mm

Fine scale

3.75mm

2.75mm

1.25mm

1mm

0.5mm

 

So long as the overall wheel width is at least twice the flange way width, the wheel cannot drop. The tyre width dimension includes the flange width when preventing wheel drop.

 

I don't see an actual problem with those figures, provided the crossing vee is not blunted.

[jim.snowdon]

Andy,

 

Slight problem, British 0-F wheels are not manufactured to BRMSB standards, nor is the track, for which the BRMSB gauge was 31.5mm, increasing to 32mm on tight curves. The Gauge 0 Guild managed to interpret the fine scale standard as 32mm on the straight, increasing with curvature, and set a flange thickness of 0.75 - 1.00mm with a constant back to back. Both are wrong, the latter significantly so. Check gauge is a fundamental value in the wheelset:track relationship, and the last thing that should be done is introduce a significant variation, well above achievable machining tolerances, and then compound it by double gauge widening.

 

In short, the current Guild standards are a mess. What we now know as 0-MF & 0-SF (31.5 and 31.25mm) I created back in Model Railway Journal #99 and subsequently wrote up as a complete update of the Guild standards, which the Guild seem to be sitting on. In the meantime, there are a growing number of British modellers who have quietly and successfully adopted the 0-MF standards and appreciated that they work better than the Guild 's 0-F standards.

 

Jim

[Simond]

I was, as Jim noted, writing in the context of full size track and wheels, and as Jim also noted, the prototype has a considerable variation in "as designed" and "as actually running when worn" wheel profiles.

 

As Andy calculated, this is give-or-take less than a fag paper in 1:45.3 and the result is likely to be a "click" - but playing the pedant game, there must always be a change in height of axle to rail if the wheel is coned.  This is simply an effect of geometry.  Even with a ramp on the blunt nose, the axle height from the top surface of a billiard-table-flat crossing will reduce as the contact point moves laterally from closure rail to wing rail, and then it will increase again as contact is transferred to the crossing V.  If the ramping and coning work well together this will be smooth and if not, it will be abrupt.

 

Wheel drop will occur if at some point there is no piece of rail that is directly below the axis of the wheel, and within the tread width.

 

My so-far limited experience of 0-MF indicates that using commercially available wheels (mainly but by no means exclusively Slaters), and the crossings I have made to date, I get a very much smoother transition than with Peco, the older, wide flangeway Marcway, or the copperclad tandem I built to GOG-F standards some 15 years ago.  I cannot be sure if this is elimination of drop or better building (My craftsmanship is probably not better than the Peco factory) or a combination of both.  In any case, it is clear that the 0-MF works well.

 

best

Simon

[Andy Reichert]

Andy,

 

Slight problem, British 0-F wheels are not manufactured to BRMSB standards, nor is the track, for which the BRMSB gauge was 31.5mm, increasing to 32mm on tight curves. The Gauge 0 Guild managed to interpret the fine scale standard as 32mm on the straight, increasing with curvature, and set a flange thickness of 0.75 - 1.00mm with a constant back to back. Both are wrong, the latter significantly so. Check gauge is a fundamental value in the wheelset:track relationship, and the last thing that should be done is introduce a significant variation, well above achievable machining tolerances, and then compound it by double gauge widening.

 

In short, the current Guild standards are a mess. What we now know as 0-MF & 0-SF (31.5 and 31.25mm) I created back in Model Railway Journal #99 and subsequently wrote up as a complete update of the Guild standards, which the Guild seem to be sitting on. In the meantime, there are a growing number of British modellers who have quietly and successfully adopted the 0-MF standards and appreciated that they work better than the Guild 's 0-F standards.

 

Jim

 

I just pasted those figures and the BRMSB mention aspect from the wheel maker's website. Presumably he is doing what he claims?

 

Are the 00-MF dimensions available on-line somewhere? I have only heard of UK O and S7 up until now.

 

Andy

[jim.snowdon]

Which wheel maker would that have been?

 

Jim

[Andy Reichert]

Post #76

 

I took the wheel data from http://www.walsallmo...andards/?k=:2::

[jim.snowdon]

Andy,

 

You suffered the misfortune of picking one of the few suppliers (of cast iron) wheels that are still in the Stone Age. We moved on from there when Slaters, followed by almost all of the other suppliers, adopted a finer profile at the fine end of the Guild standards.

 

Jim