TT-120 wheels standards

[Hobby]

Wait for the "locos with splashers" posts to come along, @mdvle! 

[Jeff Smith]

That's already been discussed on the other thread dealing with wheel standards........

[NCB]

20 hours ago, Flying Pig said:

 

If we know the maximum flangeway width and the crossing angle, we can calculate a minimum workable width for the wheels. 

 

Imagine a wheel running through a point in the facing direction.  At the crossing (frog), it has to cross the flangeway of the diverging line and without other support, it would drop into that gap and then lurch up onto the crossing nose (the tip of the frog), which is undesirable when it happens to every axle on a train.  Fortunately, additional support is provided by the wingrail on the diverging side of the crossing* but once this gets too far away the wheel will no longer be supported, so for smooth running the wheel must be wide enough to still be supported on the wingrail when it reaches the crossing nose.  If the wheel is too narrow there will be some degree of lurching.

 

*Alternatively, the wheel can be supported on its flange but this requires unrealistically deep flanges.

 

If we assume the worst case, where the wheel is running with the back of the flange against the adjacent wingrail, it's easy to work out that at the crossing nose the wheel has to span a distance of one flangeway plus another flangeway turned through the crossing angle in order to reach the diverging wingrail, plus a bit of overlap to do the actual supporting.  This gives a formula:

 

     minimum wheel width = flangeway + flangeway / cosine( crossing angle ) + a bit

 

I don't know the crossing angle of the Peco points, but assuming it's similar to their 00 and N points - i.e. between 10 and 12 degrees - then the cosine is so close to 1 that we can just say that the wheel needs to be twice the maximum flangeway plus a bit of overlap.

 

The NEM standard gives a maximum flangeway for 12mm gauge track of 1.0mm. So our minimum wheel width is 2.0mm plus a bit, which is pretty much what the NEM standard specifies (2.3 - 2.5mm) and it doesnt look like there's any real scope to narrow wheels below the NEM-specified width.

Nice. Two minor qualifications: Because of tread coning the support at the crossing nose is never quite perfect. And we could probably get away with 2.0 width; the drop would be minimal.

 

Also, Peco may be using  a smaller wing rail gap; I'm not in a position to check. If so the wheel  width  could be reduced further.

 

Edited August 27, 2022 by NCB

[D9020 Nimbus]

Perhaps it's worth pointing out that a "British" loco has been done to exact scale in HO but with NEM standard wheels — the Roco NS 500/600 class — very similar to a BR class 08. Granted it doesn't have splashers, but it does have outside frames. The valve gear on steam locos which don't have splashers is also no problem — witness the Jouef and REE "USA" tanks for instance.

 

The Fleischmann "Warship" and Bulleid coaches were pretty reasonable models too. Sure, the loco was probably over-width but that model was introduced around 1970, and things have moved on a lot since then.

[NCB]

19 hours ago, andythenorth said:

 

I don't even know where to begin. 🙂

 

I'm aware RMweb has a wide church of members....and the hobby as a whole has always attracted people with unique thought patterns.

 

But I'm really struggling with your premise.

 

If this was a different kind of website...you'd be grade A trolling in the most traditional internet sense of 'say ridiculous things to see who bites and gets wound up'. 👻

 

I suspect strongly however that you genuinely mean everything you say. 🙂

 

Perhaps it's best if we leave you all to it more generally in this TT:120 forum?

A large number of the posts make very very little sense.

Sorry you're struggling Andy. To put it simply, 3mm on 12mm track works and is probably the most flexible option. Fine scale 3mm on 14.2 mm track or 2.5mm on 12mm track could be made to work but may have constraints unacceptable to producers. May. Strict NEM  2.5 standard track and wheels can't be done with a lot of British  stock without a lot of bodging.

 

Why do you think there is no mainstream example of British  products running on scale track? Read George Mellor on it; it was the wheels.

Edited August 27, 2022 by NCB

[Grovenor]

32 minutes ago, D9020 Nimbus said:

Perhaps it's worth pointing out that a "British" loco has been done to exact scale in HO but with NEM standard wheels

So can you give details of the 'exact' dimensions over the frames, depth of axleboxes, and width over coupling rods to support your statement?

[andythenorth]

37 minutes ago, NCB said:

Sorry you're struggling Andy. To put it simply, 3mm on 12mm track works and is probably the most flexible option. Fine scale 3mm on 14.2 mm track or 2.5mm on 12mm track could be made to work but may have constraints unacceptable to producers. May.

 

It's the putting together of 2 and 2, and then coming out with 7 that I can't follow. 🙂

 

I am unable to tell if: 

1) you're simply very dedicated to finescale, and assume that RTR manufacturers will share your dedication

2) you're grieving over the perceived damage to 3mm scale and are trying to fight a rearguard action to demonstrate that TT:120 is simply impossible

3) we're talking completely past each other.

 

Which is closest to the case do you think? 🙂

 

Edited August 27, 2022 by andythenorth

[Hobby]

1 hour ago, Jeff Smith said:

That's already been discussed on the other thread dealing with wheel standards........

 

It's never stopped them in the past, Jeff! ;)

[Hobby]

47 minutes ago, NCB said:

Why do you think there is no mainstream example of British  products running on scale track? Read George Mellor on it; it was the wheels.

 

Things have moved on from his time... I don't know why you (and some others) have to keep banging on about it, they'll do some sort of compromise, just like RTR manufacturers have always done, and 99% of modellers will accept it. Finescale modellers won't, but to be quite frank I couldn't care less what they think as I'm not a finescale modellers and never intend to be. But I really wish they'd give it a rest and just wait and see.

[SD85]

5 hours ago, mdvle said:

 

The rest of the world seems to be able to produce models in HO and N where the track width matches the scale so I am sure most of the UK stuff can also be done.

 

Is it possible some of the steam stuff could be a problem?  Perhaps - but steam is now 50+ years in the past and while it would be nice to have for TT:120 it isn't necessary - though I expect steam will be available.

 

My thoughts too.

 

I don't see why diesel and electric locomotives should be an issue.

 

Nor do I see the issues in making locos to scale in TT (or H0 for that matter) where the cylinders and valve gear are below the splashers. As noted the SR USA tank loco (the prototype of which was constructed with the UK loading gauge in mind) has been done in H0 scale and that seemed to work fine. Also, DJH produced H0 scale kits for the WD 2-8-0 and 2-10-0 locomotives. Therefore it should be possible to do at least the BR Standard classes in TT and H0 scales.

 

I accept that there may be issues on some older locomotives with splashers.

Edited August 27, 2022 by SD85

[rekoboy]

I am reading the further comments on this topic and have come to the conclusion that my contribution on the BR94 0-10-0 must be invisible to many readers. From the photo it should be possible to see very clearly that very acceptable steam locos with almost fine-scale valve gear and wheels are perfectly possible in 1:120 - or do I inhabit a parallel universe? Oh, sorry, the loco is German. That doesn't count.

[Jeff Smith]

There are several threads overlapping with ideas about UK outline steam loco potential in TT.  The presence of splashers in many has been discussed as being perhaps difficult to deal with however there are some possible candidates in BR standard classes, ie 9F, and some 0-6-0s that might appeal.

[Flying Pig]

58 minutes ago, rekoboy said:

I am reading the further comments on this topic and have come to the conclusion that my contribution on the BR94 0-10-0 must be invisible to many readers

 

Strange, I read the same posts and came to the conclusion that it is impossible to post anything about TT120 that isn't manic boosterism without attracting the attentions of the thought police (a small but busy force).  Tone it down chaps - it's getting silly and repetetive.

[andythenorth]

39 minutes ago, Flying Pig said:

Tone it down chaps - it's getting silly and repetetive.

 

It's all getting a bit internet isn't it?

 

https://xkcd.com/386/

 

Toy trains at the end of the day.

[NCB]

21 hours ago, andythenorth said:

 

It's the putting together of 2 and 2, and then coming out with 7 that I can't follow. 🙂

Hi Andy. Trouble is I'm not sure which bit you're actually objecting to.

21 hours ago, andythenorth said:

I am unable to tell if: 

1) you're simply very dedicated to finescale, and assume that RTR manufacturers will share your dedication

Nope. I use what's there. What I assume RTR manufacturers are dedicated to is getting engines and the like as accurate as possible, because they get slaughtered on here if they aren't .

 

21 hours ago, andythenorth said:

2) you're grieving over the perceived damage to 3mm scale and are trying to fight a rearguard action to demonstrate that TT:120 is simply impossible

Others maybe, not me. I want some form of TT to be a commercial success, and think one would be of advantage to 3mm even if it's TT-120.

21 hours ago, andythenorth said:

3) we're talking completely past each other.

Possibly !

21 hours ago, andythenorth said:

 

Which is closest to the case do you think? 🙂

 

 

[Hobby]

19 minutes ago, NCB said:

 because they get slaughtered on here if they aren't 

 

I think you over estimate the influence of this forum. The majority of railway modellers aren't members of it and even then its only a small percentage of members that will get involved in any such discussion. I think if you look at the world beyond this forum that most modellers work on the "if it looks OK, it is OK" principle. I appreciate that finescale modellers will not understand this but that's how the world works outside the finescale modelling circles where therest of us inhabit. 

 

Manufacturers will try to get things as accurate as they can, certainly compared with the 50s and 60s, but they also know that the majority of modellers will accept some compromises to have a viable model that they can plonk on the track and run. So if its a mm or so out to allow that the majority will accept it without question and we'll enjoy using it and ignore the protestations of a small minority.

[D9020 Nimbus]

On 27/08/2022 at 16:44, Grovenor said:

So can you give details of the 'exact' dimensions over the frames, depth of axleboxes, and width over coupling rods to support your statement?

Sorry, I shouldn’t have used the word "exact". If you're interested in the dimensions they might be mentioned in the review of the Australian (VR) version of the same loco which Roco did more recently; it appeared in Continental Modeller. The model doesn't seem to have generated any adverse comment I've seen. No doubt there are compromises, but this isn't an easy loco to model. Compare the current Farish version in N, often criticised for being too wide over the connecting rods.

 

The Dutch version was introduced a long time ago — back in the 1980s I think.

[HSB]

As I said at the start most people will want to use PECO points but this thread was aimed at those modellers who, like me, would like to have models with the underframes in proportion with the bodies which is effectively impossible with NEM standard wheels and axles. The simple explanation is NEM TT axles are 18.2mm while the typical prototype distance over axle boxes scales out at only 16.9mm! 

I realise there are a lot of people who don't care about realistically proportioned models and will be happy to run whatever is thrown at them and nobody is trying to stop them doing whatever they're happy with. I'm actually coming around to the idea that it might be better if they just produce RTR models in 3mm scale as they could then be produced in correct proportions and it would be fairly easy to change the 12mm gauge wheelsets for 13.5mm or 14.2mm gauge finescale wheelsets from the 3mm Society (and FiNetracks now produce easy-to-build point kits for 14.2mm gauge). Judging from some of the comments on this thread I think a lot of people wouldn't know the difference anyway!

I do, however, believe finescale TT:120 is quite possible using the 3mm Scale finescale standards for 12mm gauge with appropriate length axles but will require quite a bit of hacking around to reduce RTR underframes to near the correct width. It may even be possible to make use of PECO track with a couple of simple modifications. Flangeways can be easily reduced with plastic strips (something I ended up doing in N gauge many years ago when I was modelling US outline) and wheel drop can be reduced with a suitably shaped sheet of plastic, wood or card in the frog gap.

Finally, to those who say wait and see what is produced, PECO points have already been shown to be compatible with NEM wheelsets and anything which is produced from now on will be made to run on PECO track which inevitably means wide wheels!

[Jeff Smith]

The answer to your last paragraph is yes.....this is also why P4 and 2mm are the finescale derivatives of 00 and N which will never be produced as RTR.......!  Established commercial wheel and track standards will prevail including TT:120.

 

Even in P4 outside cylinder crosshead clearances can be as little as a few thou......and compensation is mostly a necessity.

[Ravenser]

A Modest Proposal 

 

Rather than stagger round in ever decreasing and ever more heated circles of speculation about what may or may not be possible based on the poster's assumptions and preferences, perha[s we could start from some FACTS??  

 

Peco TT-120 points are now available in model shops . Perhaps somebody can take one, and measure the flangeways with feeler gauges? 

 

Then they could post the figures , and we can see what are the actual crossing and check flangeways, the check gauge (not to mention the Czech gauge in TT),  and the check rail span?

 

From these values it will be possible to calculate the minimum thickness wheel / wheel tread which will run through the crossing without drop in, and the maximum back to back before check rails become ineffective 

 

It will then be possible to establish the "Finest Fully Peco-Compatible Wheel" , and have a meaningful discussion about what compromises on what prototypes this might entail.

 

This will place the debate on a footing of numbers and maths, not feelings and speculation

 

As far as over-thick bogie sideframes are concerned : these should be no thicker in mm than are currently made in N gauge .

 

But in a scale 25% larger than British N, they will be 25% thinner in scale terms.

Edited August 29, 2022 by Ravenser

[Ravenser]

On 27/08/2022 at 11:26, rekoboy said:

Every time I return to this website section and see further comments on the problems of wide flanges, overscale bogie sideframes and so forth my heart sinks. At least since German reunification several European manufacturers have been producing high-quality model locos and rolling stock with, for my eyes, fine-scale appearance at relatively modest cost. Do you really think a 1:120 scale loco built to run over Tillig track looks and runs like a Triang TT product of the early 60s? Does my Kuehn BR94 have steamroller wheels and overscale toy valve gear? I do not think so. Just let yourselves be surprised and marvel at what mainstream production can do.

 

The loco has no splashers . It does have outside cylinders and valve gear , but I understand the German loading gauge is rather larger than Berne gauge so there is more room to play with.

 

Any British loco without splashers or outside valve gear should be fine

 

L&Y 2-4-2T in TT-120, anybody?

[Hobby]

Even with all the figures it'll still be speculation, Ravenser. Whatever we think might happen the chances are the manufacturers will use the same standards as already used by Tillig, Piko, etc., are already using and for what the Peco points have been designed for!! For some British locos there will be some compromises, all except a small group have accepted that already. 

 

There's your answer.

Edited August 29, 2022 by Hobby

[Grovenor]

18 hours ago, D9020 Nimbus said:

Sorry, I shouldn’t have used the word "exact".

Thank you. All people have been trying to say on here is that wheels over scale width require compromise and that this is either in the track gauge as for TT3 and 00, or in the vehicle widths around the wheels as in H0 and TT-120. You can choose your compromise but you can't avoid it except by using a proto scale.

[andythenorth]

2 hours ago, Ravenser said:

Rather than stagger round in ever decreasing and ever more heated circles of speculation about what may or may not be possible based on the poster's assumptions and preferences, perha[s we could start from some FACTS??  

+1 to this. 😉

 

Could we also have some additional lists of locomotives where the splasher, bogie sideframes or other running gear parts will simply be too thick? 

 

We can then form our own, individual subjective opinions about whether the possible lack of exact scale fidelity in locomotives that are not announced, (and may never be) causes any of the following outcomes (which have been claimed as quite likely ish):

• UK TT:120 has to be abandoned in favour of 3mm scale on 12mm track gauge
• UK TT:120 is abandoned because manufacturers simply refuse to tool locomotives with compromises in areas around the running gear because  a handful of people might then criticise on this forum
• the Peco TT:120 range is a fundamentally flawed product

There are probably multiple XKCDs that could apply here 🙃

Edited August 29, 2022 by andythenorth

[NCB]

2 hours ago, andythenorth said:

+1 to this. 😉

 

Could we also have some additional lists of locomotives where the splasher, bogie sideframes or other running gear parts will simply be too thick? 

 

We can then form our own, individual subjective opinions about whether the possible lack of exact scale fidelity in locomotives that are not announced, (and may never be) causes any of the following outcomes (which have been claimed as quite likely ish):

• UK TT:120 has to be abandoned in favour of 3mm scale on 12mm track gauge
• UK TT:120 is abandoned because manufacturers simply refuse to tool locomotives with compromises in areas around the running gear because  a handful of people might then criticise on this forum
• the Peco TT:120 range is a fundamentally flawed product

There are probably multiple XKCDs that could apply here 🙃

Here's some examples, in 3mm:

Mitchell Manor. Problems: None! That sensible man Collett put the cylinders far enough forward fot the crossheads not to clash with the leading crankpin. Also, he used wide footplates and generous splashers with plenty of room for wheels.

Worsley 42xx. Problems: Crosshead clashes with leading crankpin. On the prototype they recessed the crankpin into the coupling rod and the clearance is still frightening. I drifted the cylinders out and filed the crankpin nut to half thickness, and it still gives problems.

 

Mitchell 517 class. Problems: Typical Dean  narrow footplate and narrow splashers. I removed the splashers, fixed them further out and allowed zero sideplay on the leading drivers,  but it's still very tight.

3mm Society Dean goods white metal kit. Problems: same as 517. I thinned the splasher sides and it works, just.

Edited August 29, 2022 by NCB