Set-track curves and Streamline track spacing

[Chimer]

I've just accidentally discovered something which I think is going to simplify my layout design process, so I thought I might as well share it ..... with apologies to everyone who's worked it out already!

 

For me to achieve what I want in the space I've got means I'm going to need tight (max 2' radius) hidden 90 degree double track bends in (most likely) 3 out of 4 corners.  I don't trust myself to form flexi at such sharp radii so intend to use radius 3 & 4 Set-track curves.  But the pointwork will be Streamline, so the ruling track spacing will be 2", while of course Set-track spacing is 2.625", so a tweak is required to use the two together.  Something I was illustrating for another member caused a lightbulb moment which resulted in me producing this trivial little track plan (Set-track curves in green) ....

 

 

I did the outer R4 curve and the straights, at 2" centres, then placed the middle 45 degrees of R3 correctly (2.625" inside) relative to the R4 curve, so there is no risk of  coming togethers.  It was then just a matter of fiddling about to establish where the odd 22.5 degrees of R3 on each end had to be placed to line up with both the 45 and the incoming straight.  Clearly, the R3 curve has to start earlier than the R4.  To be exact, 1.5" earlier, and that's the point (at last !) - it means the effective centre-line radius of the outside track is R4 + 1.5", i.e. 24", so instead of fiddling about with the actual Set-track radii when planning, I can just use 90 degrees of parallel 22" and 24" curves (centre lines shown in purple) to plan my bends.  Obviously when laid it won't look like that, but as I said earlier these curves will be hidden anyway.

 

For completeness, the mini straights needed between the 22.5 and 45 degree sections on the inner curve are (according to XTrackCad) 1.625", which is, spookily, the length of the Set-track Special Short Straight (ST-203).

 

I hope that might be of interest to somebody on a quiet Sunday afternoon - describing it has kept me busy for a while anyway 

[Wheatley]

Try it out in practice with real track and your longest / most overhanging stock, you may find it comes into conflict at the ends of the curves. Mine did. 

[Keith Addenbrooke]

Hi Chris, that could be really useful  - especially for hard to reach hidden corners (where transition curves aren’t needed and space is at a premium).  For curves less than 2’ radius, I’ve often seen it recommended that Setrack be used for the reasons you suggest - scenic sections can still have Code 75 with appropriate joiners if desired.

 

Unfortunately for me, in my parallel universe this quiet afternoon, I’ve been playing with full length 85’ US outline coaches, which just don’t look good on 3rd radius curves...

 

 

 

(Photos from my Diorama build thread)

Edited October 7, 2022 by Keith Addenbrooke
Reinstating photos

[Chimer]

3 minutes ago, Wheatley said:

Try it out in practice with real track and your longest / most overhanging stock, you may find it comes into conflict at the ends of the curves. Mine did. 

 

I've nothing longer than Mk 1s, so I think the offsetting of the curve starts will see me OK.  But a useful reminder, thanks.

[Chimer]

4 minutes ago, Keith Addenbrooke said:

Hi Chris, that could be really useful  - especially for hard to reach hidden corners (where transition curves aren’t needed and space is at a premium).  For curves less than 2’ radius, I’ve often seen it recommended that Setrack be used exactly as you suggest - scenic sections can still have Code 75 with appropriate joiners if desired.

 

Unfortunately for me, in my parallel universe this quiet afternoon, I’ve been playing with full length 85’ US outline coaches, which just don’t look good on 3rd radius curves...

 

 

 

(Photos also appear on my Diorama build thread)

 

Oh wow!  Can they even get past one another on R3/R4 at full Set-track centres?

[Pete the Elaner]

Overhang can be a problem as well as underhang.

We all think of the inside issue with a coach (particularly a Mk3, which also has a lot of end overhang) but something like a Princess can have quite a lot of front end overhang.

[Keith Addenbrooke]

14 minutes ago, Chimer said:

 

Oh wow!  Can they even get past one another on R3/R4 at full Set-track centres?

I don’t know - I haven’t got any 4th radius track to test properly.  The more basic problem was persuading them to go round the 3rd radius at all: minimum recommended radius seems to be 2’

[Keith Addenbrooke]

17 minutes ago, Pete the Elaner said:

Overhang can be a problem as well as underhang.

We all think of the inside issue with a coach (particularly a Mk3, which also has a lot of end overhang) but something like a Princess can have quite a lot of front end overhang.

Good point - it’s not just the big locos either: small 4-4-0 tender locos can have a lot of front end overhang too.

[DCB]

It does depend on your stock how much clearance you need, if you run modern image 75ft MK3 stock on the outer with a big overhang (underhang?) on the inside and  Modern image preserved Tender drive Hornby Kings on the inner with a big outside overhang then you have a problem. However the pinch point is the long front overhang loco on the inside entering the bend as a long underhang coach leaves.  Leaving the curve the max overhang is when the coach underhang is minimum,   You might find it better to use 3rd Radius throughout both inner and outer curves.. and add straights at the ends of the curves,  see doodle.   I only bother with getting enough clearance for trains travelling in the usual direction,  I don't run wrong line so it's not relevant.

 

 

 

Edited November 5, 2020 by DavidCBroad

[Chimer]

16 hours ago, DavidCBroad said:

You might find it better to use 3rd Radius throughout both inner and outer curves.. and add straights at the ends of the curves,  see doodle. 

 

That is completely counter-intuitive, absolutely correct, and gives substantially more extra room than your doodle suggests.  Looks very odd, but who cares if it's all out of sight?

 

Genius!!

[Mike Buckner]

and the same trick works if both curves are R4 or both curves are R2

[Keith Addenbrooke]

1 hour ago, Chimer said:

 

That is completely counter-intuitive, absolutely correct, and gives substantially more extra room than your doodle suggests.  Looks very odd, but who cares if it's all out of sight?

 

Genius!!

Agree totally - added to which, it may well be that you / people / I have a complete circle of R3 track pieces ‘in stock’ (some train sets also now come with them, I believe), so already have the pieces needed for 2 x double track right hand corners using this approach, making this a kind of zero cost solution too.

[Mike Buckner]

Here is a way to join a segment with Peco spacing to one with Setrack spacing, using Setrack turnouts & curves, Streamline turnouts and a straight cut to length.  In fact all you need is the two ST-227 tracks. The other tracks are just proof of concept.

 

Edited November 6, 2020 by Mike Buckner
typo

[Largechris]

On 05/11/2020 at 16:54, Chimer said:

 

That is completely counter-intuitive, absolutely correct, and gives substantially more extra room than your doodle suggests.  Looks very odd, but who cares if it's all out of sight?

 

Genius!!

I’ve just done exactly this in one corner for the same reason (job lot of the same radius) and it works great.

 

Because of this thread I’m now trying to convince myself I’m a geometrical genius. 

[TonyMay]

On 07/11/2020 at 03:21, Mike Buckner said:

Here is a way to join a segment with Peco spacing to one with Setrack spacing, using Setrack turnouts & curves, Streamline turnouts and a straight cut to length.  In fact all you need is the two ST-227 tracks. The other tracks are just proof of concept.

 

 

Yes, but that means introducing an unsightly kink in the track.  If you put the whole thing on a slight curve (it only needs to be a few degrees), then the change is hardly noticeable.

[AndyID]

On 05/11/2020 at 09:00, Mike Buckner said:

and the same trick works if both curves are R4 or both curves are R2

 

Yes, I was going to suggest using R2 for both. It won't look too great but they are hidden so who cares.

[Chimer]

For me, R2 is too tight, whether hidden or not.

[dagrizz]

On 01/11/2020 at 14:25, Chimer said:

I've just accidentally discovered something which I think is going to simplify my layout design process, so I thought I might as well share it ..... with apologies to everyone who's worked it out already!

 

 

 

Thanks for starting this thread. I'm just planning my next layout and was intending to use R3 and R4 curves for the corners and streamline elsewhere and I was pondering how to mix the two track spacings.

 

Graham