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21mm discussion

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Horsetan
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It's a pity we can't get something like the fast track base in 21mm. That would open up the gauge to many new layouts, especially bigger layouts

 

It would certainly cut down the time needed to lay plain track, which means you can concentrate on the pointwork.

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Hmmm it would be good to have that in 21mm. I certainly would not build a larger layout 21mm by hand but if the track existed …..

 

Definitely. The reason many people do not go for 21mm is the prospect of having to build lots and lots of track. Of course many do, and to an excellent standard, but I couldn't possibly imagine going to 21mm gauge,

As layout no.2 would be a large layout, and a pain in the ass to build all the track. Modelling the 1950s means that the bulk of my locos would be kit built and therefore 21mm compatible. If the fast track was there, I would seriously consider, going to 21mm..

Just my ramblings..

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Definitely. The reason many people do not go for 21mm is the prospect of having to build lots and lots of track. Of course many do, and to an excellent standard, but I couldn't possibly imagine going to 21mm gauge,

As layout no.2 would be a large layout, and a pain in the ass to build all the track. Modelling the 1950s means that the bulk of my locos would be kit built and therefore 21mm compatible. If the fast track was there, I would seriously consider, going to 21mm..

Just my ramblings..

 

I could also be tempted to go to 21mm - if it was possible to do it without becoming suicidal.

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I could also be tempted to go to 21mm - if it was possible to do it without becoming suicidal.

I think that putting new wheel sets and bogies on all the stock would be more than enough work for me. Am i correct in thinking that you could lay 21mm on an existing HO layout as they clearances/loading gauge would be the same. Would the spacing between the track centres remain the same?

and if so, would the points have a less acute angles or need to be longer on the crossovers?

Edited by DiveController
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I thin that putting new wheel sets and bogies on all the stock would be more than enough work for me. Am i correct in think that you could lay 21mm on an existing HO layout as they clearances/loading gauge would be the same. Would the spacing between the track centres remain the same?

and if so, would the points have a less acute angles or need to be longer on the crossovers?

 

You cannot retain the kind of sharp radius curves and angles that are common in OO, unless you are portraying something like the CSET beet factory or Guinness internal lines

 

For 21mm, 3ft radius would be pushing your luck.

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You cannot retain the kind of sharp radius curves and angles that are common in OO, unless you are portraying something like the CSET beet factory or Guinness internal lines

 

For 21mm, 3ft radius would be pushing your luck.

Yes, I see your point, Ivan. Assuming no tight curves are the track centers usually spaced the same in 21mm versus 16mm or are the tracks spaced wider apart? Having not thought about anything other than OO on HO before, I'm just trying to get some basic info right in my head here.

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Yes, I see your point, Ivan. Assuming no tight curves are the track centers usually spaced the same in 21mm versus 16mm or are the tracks spaced wider apart? Having not thought about anything other than OO on HO before, I'm just trying to get some basic info right in my head here.

 

If we were to look at the track centre from - for example- the edge of a platform, in 21mm this would be further out by about 2.25mm.

 

Between two running lines, you would still need to ensure that you preserve the distance between them so that trains pass each other. Hence you would be using clearances that are much more a scale representation of the real thing.

 

I think there are diagrams which show the kind of clearances you need. Some are here.

 

These are the clearances we might use in P4/18.83, but you can see how the principles apply in 21mm gauge.

Edited by Horsetan
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If we were to look at the track centre from - for example- the edge of a platform, in 21mm this would be further out by about 2.25mm.

 

 

Why would the centre line be further out, since whether modelling with 16.5mm or 21mm gauge, the centre line of the track is the centre line of rolling stock and moving it out by 2.25mm would increase the gap between rolling stock and the platform. I could understand moving the centre line of the track if the rolling stock was to be built to the wider Irish loading gauge, but if the stock runs fine past platforms on 16.5mm track, there would be no need to move the track centre.

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Why would the centre line be further out, since whether modelling with 16.5mm or 21mm gauge, the centre line of the track is the centre line of rolling stock and moving it out by 2.25mm would increase the gap between rolling stock and the platform. I could understand moving the centre line of the track if the rolling stock was to be built to the wider Irish loading gauge, but if the stock runs fine past platforms on 16.5mm track, there would be no need to move the track centre.

 

That's my understanding, too - the centre-lines remain the same, regardless of the track gauge - it's only a loading gauge change that would cause an issue.

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the centre-lines remain the same, regardless of the track gauge - it's only a loading gauge change that would cause an issue

That's what I was thinking, that the centers remained the same if the stock remained the same. I confused the issue by mentioning loading gauge since obviously more serious modelers are modeling wider stock, although I think I will be running rtr OO stock, Murphy, Provincial etc. Just to clarify things though, models like the MM cravens for example are modeled correctly to scale widths except the bogies/wheels, correct? Ivan, thanks for those links,some more reading to be done.

 

I presume point work on the 21mm has to be much longer than in 16mm for the same reason you cannot have curves that are as tight?

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Why would the centre line be further out, since whether modelling with 16.5mm or 21mm gauge, the centre line of the track is the centre line of rolling stock and moving it out by 2.25mm would increase the gap between rolling stock and the platform. I could understand moving the centre line of the track if the rolling stock was to be built to the wider Irish loading gauge, but if the stock runs fine past platforms on 16.5mm track, there would be no need to move the track centre.

 

If we assume that the distance between the platform edge and the nearest rail remains constant then the centre line is moved out in 21mm gauge by virtue of the wider track - i.e. the distance from the rail nearest to the platform to the centre line of the track is 8.25mm in 16.5mm track and 10.5mm in 21mm gauge track.

Platform to Track Centre.jpg

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If we assume that the distance between the platform edge and the nearest rail remains constant then the centre line is moved out in 21mm gauge by virtue of the wider track - i.e. the distance from the rail nearest to the platform to the centre line of the track is 8.25mm in 16.5mm track and 10.5mm in 21mm gauge track.

[ATTACH=CONFIG]23301[/ATTACH]

 

If you are modelling 00 track but positioning it to handle the wider Irish stock, then the track centres DO NOT move when you move to 21mm ( think of it simply as the wheels moving out towards the body sides , but nothing else changes . If your current track centre's in 00 are adequate for your stock clearances , then the same track centres will typically suffice for 21mm.

 

By and large , Peco centres accommodate overhangs and platform distances that are adequate for irish stock so , again track centres dont move. 21mm takes up really no more real estate space, other then the fact that the sleepers are a little longer as the compromise that is 00 for sleepers goes away . PECO is 55mm centred and UK real life is 45mm in 4mm/ft . I believe Irish track standards had a wider centre then UK ones anyway ./ Track spacing isn't consistent anyway and changes with the radius .

 

Note also that 21mm has nothing to do with small radius , you are mixing up p4 and 21mm . for me for example I would build to EM flange standards and 21mm , that would allow standard RP25 wheels to run. There is no requirement to switch to p4 track standards merely to access 21mm

 

21mm will happily go round settrack radius if you want to design it for that . The key is flange and back to back clearances ( and axle movement )

 

 

I presume point work on the 21mm has to be much longer than in 16mm for the same reason you cannot have curves that are as tight?

 

Again , you can build settrack style pointwork quite happily in 21mm if you so want , it needn't be any longer then PECO ( and in fact it can be actually smaller)

 

IN fact as I understand it the "6 foot" in ireland is actually "9 foot', so that would give the PECO standard separation of 55mm just about right for 21mm !! ( on level straight track)

Edited by Junctionmad
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