Double track at 3rd radius

Any questions about designing a model railway layout or problems with track work.
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pete12345
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Double track at 3rd radius

Postby pete12345 » Tue May 12, 2020 8:40 pm

I have two corners on my plan which will be hidden from view. The plan is to lay the inner track using some 3rd radius curves I have lying around. The question is, how is best to lay the outer track? I could use flexi to continue round at 50mm spacing, but I have concerns about clearances with coach overhang around the curves. Wider track centres and using 4th radius is one solution, but how to smoothly increase the spacing without it looking odd? What have people done when using streamline-standard double track and reasonably tight curves?
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Bufferstop
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Re: Double track at 3rd radius

Postby Bufferstop » Tue May 12, 2020 11:30 pm

If they are hidden from view you can afford to vary the spacing to clear your longest overhangs and bring it back to 50mm before it comes back into view. What the eye doesn't see and all that.
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Dad-1
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Re: Double track at 3rd radius

Postby Dad-1 » Wed May 13, 2020 9:13 am

pete12345,

I'd go with flexi. After the 3rd radius is secured in some way and mark the longest coach you have.
temporarily fix (drawing pins ?) the flexi and double check those long coach clearances.

To get a regular, or variable 6 foot I use cut off lengths of coffee stirrer/lolly stick to the required length and
locate against in your case 3rd radius sleepers. Springing slightly pre-formed flexi tracks sleepers against and
fix as necessary. With careful and consistent laying I'd defy anyone to notice any gradual widening.

Just a thought perhaps another idea to try ?
It's the method I used for a consistent closer twin track laying on my Thomas layouts where short stock would
be used and I wanted to have track to run outside 1st radius 180 turns, but somewhat tighter than 2nd radius.

Geoff T.
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Bigmet
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Re: Double track at 3rd radius

Postby Bigmet » Wed May 13, 2020 2:13 pm

Bufferstop wrote:If they are hidden from view you can afford to vary the spacing to clear your longest overhangs and bring it back to 50mm before it comes back into view. What the eye doesn't see and all that.

I share that last opinion, and there's a simple way to get back to the 50mm centres without risk of collisions too, if you have enough R3 pieces to make both the inside and outside track curves. From the parallel Streamline track at 50mm centres:

For a 90 degree turn, start the inside curve 50 mm before the outside curve: the Streamline spacing of 50mm will be present at the end of the curves.

For a 180 degree turn, start the inside curve 67 mm before the outside curve, at the midpoint of the outside curve, insert a 100mm length of straight flexi track, then complete the curve with 3rd radius: the Streamline spacing of 50mm will be present at the end of the curves.

The curves won't have the neatly concentric effect of R4 or a flexitrack curve, but then they are not on view. This was a regular procedure back in the day when R3 was the largest set track radius available, and flexitrack didn't easily go below 24" radius, for making the return curves for a reasonably compact double track circuit.

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pete12345
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Re: Double track at 3rd radius

Postby pete12345 » Wed May 13, 2020 9:25 pm

That's probably what I'll do then, I couldn't quite figure out the straight lengths required but now it seems so simple! It will be hidden so as long as the end overhang of a longer coach doesn't conflict on entry to the inner curve it will be fine. My 3rd radius track is all steel (and there will be also some brass Fleischmann points in the fiddle yard) but it should be ok given frequent running. I'll probably buy or build a cleaning wagon to run round and ease the upkeep a bit.

I have an old hornby planbook which demonstrates the use of flexitrack. The example given is laying a track outside a 3rd radius curve at their standard 67mm spacing. This is despite every plan in the book using 1st radius somewhere!
Once an engine attached to a train, was afraid of a few drops of rain...

Bigmet
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Re: Double track at 3rd radius

Postby Bigmet » Thu May 14, 2020 10:01 am

pete12345 wrote:... It will be hidden so as long as the end overhang of a longer coach doesn't conflict on entry to the inner curve it will be fine...
I should really have asked what your longest twin bogie loco, coach or wagon will be. What I described will definitely work for scale length BR mk1 and Derby and EE type 4 diesels. If operating really long modern stock, then it would be best to do a test of the arrangement before fixing the track down. (Do you know, I haven't a clue just what the maximum overall lengths and maximum length between bogie pivots are now for UK stock.

pete12345 wrote: ... My 3rd radius track is all steel (and there will be also some brass Fleischmann points in the fiddle yard) but it should be ok given frequent running...
Regular running is often underestimated as a contributor to a reliable layout, but it really works. All metal wheels are a real help too. I would bond the set track pieces by soldering wire links between them, if not feeding each piece from a bus wire. Poor connections by the railjoiners are the bane of set track, if the pieces have seen a lot of assembly and disassembly over the years.

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pete12345
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Re: Double track at 3rd radius

Postby pete12345 » Thu May 14, 2020 10:47 am

The longest items I have are some 1990s mk4 carriages, which won't see regular use but it would at least be good not to have to worry about them. I'll experiment with them and anything else should be fine!

A lot of my stock has either all-metal wheels or at least metal tyres on plastic wheels. As for the rest, there will be some rewheeling going on as part of a longer plan to generally improve my older stock with close coupling, scale wheels etc.
Once an engine attached to a train, was afraid of a few drops of rain...


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