2mm Scale Association wheel rims for TT120

[natterjack]

Hi

 

I'm not a 2mm modeller but  the advent of Hornby TT120 has had me musing on its longer term options for loco scratch building in. Would anyone have any thoughts as to the suitability of the 2mm Scale Association tyre profile for running on what I understand to be close to an N Gauge dimension rail?

[Caley Jim]

It's not the rail dimensions which are critical, but the wheel profile, back-to-back dimensions and check and wing rail clearances which are important.  These things have to integrate with one another as is the case with the 2MMSA track standards.   There was discussion on here recently as to whether 2MMSA wheels could be made to run through N-gauge turnouts, or vice versa, the answer being 'no'.

 

Jim

[Nigelcliffe]

As per Jim's comment....   what I've seen of TT120 from both Hornby and Peco, the crossing clearances are quite large, and fairly "coarse scale". 

 

Peco say they are following the NEM standards for 12mm track, which have crossing clearances of 0.9mm min , 1.0mm max and check gauge 11.0mm min.   And wheel back-to-back of 10.3, wheel width of 2.4mm (inc flange), flange thickness of 0.7mm.   

As a standard its quite a bit larger in its key clearances than N, which is what one would expect for something which can operate on tight radius "trainset" curves.

 

 

A 2mm wheel won't work, it will fall into the crossings.  The NEM standard TT wheel is close to an EM wheel, and somewhat wider/fatter than a typical N wheel.   

 

- Nigel

[natterjack]

Thanks for the replies- from what I gather it could be made to work but would likely be limited to continuous parallel track and gentle curves? Probably a bit impracticable.

 

Les

[Izzy]

7 hours ago, natterjack said:

Thanks for the replies- from what I gather it could be made to work but would likely be limited to continuous parallel track and gentle curves? Probably a bit impracticable.

 

Les

Yes, totally impracticable. It’s the narrow tread width - just 1.0mm - that would be the main obstacle. Needs to be double that for TT at the very least. Romford/Markits/3mm society wheels would be a starting point I would think. 
 

Bob

[2mm Dabbler]

What's the likelihood that someone has already formulated wheel and track standards for finescale 1:120 ? 

🤔

[HSB]

34 minutes ago, 2mm Dabbler said:

What's the likelihood that someone has already formulated wheel and track standards for finescale 1:120 ? 

🤔

The 3mm Society have finescale standards for 12mm gauge which I'm planning to experiment with in the near future.

[bécasse]

4 hours ago, Izzy said:

Yes, totally impracticable. It’s the narrow tread width - just 1.0mm - that would be the main obstacle. Needs to be double that for TT at the very least. Romford/Markits/3mm society wheels would be a starting point I would think. 
 

Given that the fine scale TT being talked about is 1:120, or effectively 2,5FS, a tread width of 1,0 mm should be practical.

 

P4 (effectively "4FS") standards require a minimum tyre width of 1,85 mm, which after deducting the 0,35 mm effective flange width gives a tread width of 1,50 mm. Using the equation (2,5/4)*1,50 suggests an equivalent minimum tread width of 0,875 mm for 2,5FS.

Edited December 28, 2022 by bécasse

[natterjack]

My initial interest is for 19 spoke wheels with a diameter in the order of 14mm (14.4 to be exact) for which a 2mm scale tyre is available to fit onto a 3D printed core, hence the original query.

 

I'll be exploring  tyre only options with the 3mm Society.

 

 

[Izzy]

3 hours ago, bécasse said:

Given that the fine scale TT being talked about is 1:120, or effectively 2,5FS, a tread width of 1,0 mm should be practical.

Sorry, hadn’t realised it was, there’s no mention in the OP. I  was thus going by the table posted in the TT120 section re NEM/NMRA track standards for it.

[Chris Higgs]

6 hours ago, bécasse said:

Given that the fine scale TT being talked about is 1:120, or effectively 2,5FS, a tread width of 1,0 mm should be practical.

 

P4 (effectively "4FS") standards require a minimum tyre width of 1,85 mm, which after deducting the 0,35 mm effective flange width gives a tread width of 1,50 mm. Using the equation (2,5/4)*1,50 suggests an equivalent minimum tread width of 0,875 mm for 2,5FS.

 

To compare 2FS to P4 is not really that valid in my view. The equivalent of 2FS in 4mm scale would be EM standards. The tread width you suggest for TT120 would require pretty much scale checkrail gaps, which is not what 2FS has. Our checkrail gaps are 0.5mm, whereas true-to-scale would be about 0.3mm.

 

Pendon use an EM-Fine standard (more or less P4 tyre widths but with EM flanges). 

 

Chris

[bécasse]

58 minutes ago, Chris Higgs said:

 

To compare 2FS to P4 is not really that valid in my view. The equivalent of 2FS in 4mm scale would be EM standards. The tread width you suggest for TT120 would require pretty much scale checkrail gaps, which is not what 2FS has. Our checkrail gaps are 0.5mm, whereas true-to-scale would be about 0.3mm.

 

Pendon use an EM-Fine standard (more or less P4 tyre widths but with EM flanges). 

 

I was aware of that, it's particularly obvious (at least to a very old hand at P4) when looking at close-up photos of some of the fine locos that appear in this section - Tim's and Gerry's, for example - when compared with similar photos of comparable P4 locos, but not only doesn't it invalidate my argument, it rather reinforces it, although I would perhaps have been wiser to refer to P2,5 or P120 than 2,5FS. To me it seems that 2FS tyres would be perfectly usable for a skilled modeller working in such a scale, with their approximate EM÷2 equivalence actually being the key to their acceptability.

 

Ironically, well over half-a-century ago I actually experimented with a ¾ version of P4 (so P3 or P100) at a time when the fledgling 3mm Society seemed to be promoting a 13,5 mm track gauge as their fine scale offering, but the opportunity to partake in the construction of a pioneer P4 layout quickly knocked that particular project on the head.

[Klaus ojo]

On 20/12/2022 at 17:35, natterjack said:

Hi

 

I'm not a 2mm modeller but  the advent of Hornby TT120 has had me musing on its longer term options for loco scratch building in. Would anyone have any thoughts as to the suitability of the 2mm Scale Association tyre profile for running on what I understand to be close to an N Gauge dimension rail?

Just to confirm Jim´s first answer and oppose the same moment:

You can´t really run the wheels on N gauge pointwork. But you can pretty well run 2mm wheels on something like N gauge rail as long as you are constructing your pointwork to the 2mm standards or your adaption to this standard to your needs just like the FREMO people on the continent do with FS160.

But why should you do this extra effort if you did not want to mix N gauge/TT and 2/3mm or use RTR railwork? Mixing would cause the major problems as you would need pointwork being able to cope with e.g. 2mmFS and N gauge. Trailing switches or moveable crossings noses or wing rails are possible solutions. All causing more work at construction, maintenance and care and trouble at operation.  The photo is showing my approach and it is not yet really tested. Let´s see how it fails... (No check rails because not needed and would only cause a problem)

happy modelling!

Klaus

Edited December 29, 2022 by Klaus ojo
spelling/3mm

[Grovenor]

Proto120 standards were defined by the MRSG (Model Railway Study Group) the developers of P4 back in 1966 or 67. But to use scale wheels you need to produce scale track to run on. And you will also, presumably like to have scale dimensioned stock to run on it and hence all the Hornby TT120 will need chassis rebuilds and the locos with splashers will need them relocating to suit.

See https://www.scalefour.org/history/protofoursociety/manual/2.0-proto-ratio

But at least anyone who wants to try P120 has a set of dimensions all worked out and ready.

Edited December 28, 2022 by Grovenor

[melmerby]

2 hours ago, Klaus ojo said:

Just to confirm Jim´s first answer and oppose the same moment:

You can´t really run the wheels on N gauge pointwork. But you can pretty well run 2mm wheels on something like N gauge rail as long as you are constructing your pointwork to the 2mm standards or your adation to this standard to your needs just like the FREMO people on the continent do with FS160.

But why should you do this extra effort if you did not want to mix N gauge/TT and 2/3mm or use RTR railwork? Mixing would cause the major problems as you would need pointwork being able to cope with e.g. 2mmFS and N gauge. Trailing switches or moveable crossings noses or wing rails are possible solutions. All causing more work at construction, maintenance and care and trouble at operation.  The photo is showing my approach and it is not yet really tested. Let´s see how it fails... (No check rails because not needed and would only cause a problem)

happy modelling!

Klaus

Shades of Wrenn 00 fibre based points there.

[Izzy]

10 hours ago, Grovenor said:

Proto120 standards were defined by the MRSG (Model Railway Study Group) the developers of P4 back in 1966 or 67. But to use scale wheels you need to produce scale track to run on. And you will also, presumably like to have scale dimensioned stock to run on it and hence all the Hornby TT120 will need chassis rebuilds and the locos with splashers will need them relocating to suit.

See https://www.scalefour.org/history/protofoursociety/manual/2.0-proto-ratio

But at least anyone who wants to try P120 has a set of dimensions all worked out and ready.

That makes interesting reading. Not sure I would want to try 2FS with under 0.2mm deep flanges …. I’ve gone to using 0.5mm with P4 to save me hassle in recent years. 
 

Bob 

[bécasse]

If I were to try P120 using 2FS tyres, I would probably use 2FS rail as well (which at code 40 would be underscale but not by much, particularly for s/hand rail used on secondary routes, etc.) so the wheel/rail interface shouldn't be a problem, I would also use the 2FS standards for setting check rails gaps etc. Inevitably these won't be quite the same as those set by the MRSG six decades ago, but they work (and work well) and will be very little different visually to those set by the MRSG.

 

However, as Keith strongly hints above, it would be a brave - and very dedicated - person who took on all the work involved. I look, with great admiration, at what many 2FSers achieve in terms of their overall layouts, and they have life easy compared with anyone following the P120 route.

[Chris Higgs]

15 hours ago, Grovenor said:

Proto120 standards were defined by the MRSG (Model Railway Study Group) the developers of P4 back in 1966 or 67. But to use scale wheels you need to produce scale track to run on. And you will also, presumably like to have scale dimensioned stock to run on it and hence all the Hornby TT120 will need chassis rebuilds and the locos with splashers will need them relocating to suit.

See https://www.scalefour.org/history/protofoursociety/manual/2.0-proto-ratio

But at least anyone who wants to try P120 has a set of dimensions all worked out and ready.

 

12mm track gauge is pretty much bang-on true scale for 1:120. So I am pretty sure you would not need to move the splashers, they will already be plenty wide enough for finer wheels. The only thing you would have to do is adjust the check and wing rail gaps on TT120 points to match. Hmm, that actually makes it easier to do than if modelling in either 2FS or P4.

 

So is TT120 the only (UK) RTR scale where the track gauge is correct?

 

We don't have to move splashers on RTR locos in 2mm for the same reason, both N and 2FS end up with a total width over wheelsets which is wider then prototype, so the splashers have already been set to match this.

 

You could use code 40 rail, but secondary track doesn't really match the loco stock available from Hornby, which seems to just be top-link ECML.  

 

Chris  

[Ian Morgan]

5 hours ago, Chris Higgs said:

So is TT120 the only (UK) RTR scale where the track gauge is correct?

 

 

Well, 009 would be correct for 2 foot 3 inch gauge prototypes, but are there any RTR models for Talyllyn, Campbeltown & Machrihanish, Corris or other such systems yet?

 

Edit: just found the soon-to-be-released Bachmann 009 model of the Fletcher Jennings 0-4-2 "Tallyllyn", so that could be the first true scale/gauge UK RTR locomotive there has ever been.

 

[Grovenor]

6 hours ago, Chris Higgs said:

 

12mm track gauge is pretty much bang-on true scale for 1:120. So I am pretty sure you would not need to move the splashers, they will already be plenty wide enough for finer wheels.

Chris  

I would assume anyone wanting to have accurate scale wheels and track will want to have accurate bodies on their prize locos as well. Why go to that trouble otherwise? So splasher much closer to the footplate edge than they should be are not going to cut it.

 

It seems curious to me that Hornby make such a fuss about the track gauge being to the correct scale when pretty much every other dimension of their track is not and they have to make real compromises on the dimensions of all of the stock where the width over wheelsets affects them.

[Chris Higgs]

22 hours ago, Grovenor said:

I would assume anyone wanting to have accurate scale wheels and track will want to have accurate bodies on their prize locos as well. Why go to that trouble otherwise? So splasher much closer to the footplate edge than they should be are not going to cut it.

 

 

Hmm, 2FS modellers make a great fuss about the track gauge being absolutely correct but accept over-width wheels and splashers. 😉

 

Chris

[Nigelcliffe]

On 29/12/2022 at 19:15, Ian Morgan said:

 

Well, 009 would be correct for 2 foot 3 inch gauge prototypes, but are there any RTR models for Talyllyn, Campbeltown & Machrihanish, Corris or other such systems yet?

 

Edit: just found the soon-to-be-released Bachmann 009 model of the Fletcher Jennings 0-4-2 "Tallyllyn", so that could be the first true scale/gauge UK RTR locomotive there has ever been.

 

 

Not counting the various UK-Outline RTR HO stuff I recall from when I was a teenager.....   

 

-  Nigel

 

[Chris Higgs]

4 minutes ago, Nigelcliffe said:

 

Not counting the various UK-Outline RTR HO stuff I recall from when I was a teenager.....   

 

-  Nigel

 

 

Yes, it is many a long year since I have seen a Fleischmann Warship.

 

I suspect UK TT120 outline will go the same way as the HO stuff. Although it is not up against  an established scale (OO) with masses of RTR this time.

 

Chris