Of Reverse curves and flex track.

[Julia]

 

I am Working on my H0e modular layout, and have come up a little stuck with the connection between two modules, where due to a small over sight, the two modules I have already started, have their track meeting 50mm out of alignment. The two modules I currently have are both 800mm x 300mm, on the right hand module the track meets the end plate 150mm from the front of the module. On the left hand module the track arrives at the end plate 100mm from the front. I am thinking of making a 3rd module, also 800mm x 300mm, and on the left side I anchor a piece of track at the 100mm mark, then on the right hand side, anchor it at 150mm. In my mind this would produce a smooth flowing slightly S curve from one position to the other, with a reverse curve in the middle. My longest item of rolling stock is 150mm in length. Is that S curve going to bite me on the behind? or will there be enough of a straight with it to not be a problem? 

 

J

[ikcdab]

When I first read this,  I thought "oh no", avoid reverse curves wherever possible.  They are generally bad new on model railways where the radii tend to be tight.

However, a 50mm shift over 800m length doesn't sound too bad and I would think would work ok.

[DCB]

Probably more realistic than straight track.  The MSWJR through my neck of the woods was a series of reverse curves from Withington to Foss Cross as it climbed the side of the Coln valley and thread its way between church, and the recently built  Chapel and School.  The only real straight was the tunnel.   Narrow gauge was better still at winding round.

2" over 32" is negligible.  My straights are twistier than that!  Might be worth having a short piece of set track at the ends if its available in H0e so if it does straighten it won't affect the join.

Edited November 29, 2021 by DCB

[ITG]

11 hours ago, Julia said:

In my mind this would produce a smooth flowing slightly S curve

Why in your mind? You could draw full size what this would look like. Maybe on the reverse side of a piece of left over wall paper, or even on a few sheets of taped together A4. That way you’ll better visualise the effect of the snake.

[DCB]

Might be easier to just flex a bit of flexi across the kitchen table.

[Harlequin]

What you are proposing shouldn't be a problem. This is a simple smooth curve and there's plenty of room to add straights at the ends or in the middle if you wanted. (A 150mm straight in the middle would guarantee no reverse curve issues with your stock if you were really paranoid about it.)

Edited May 7, 2022 by Harlequin

[Julia]

2 hours ago, Harlequin said:

What you are proposing shouldn't be a problem. This is a simple smooth curve and there's plenty of room to add straights at the ends or in the middle if you wanted. (A 150mm straight in the middle would guarantee no reverse curve issues with your stock if you were really paranoid about it.)

 

Perfect! That gives me the visual I need. To my eye at this scale the bit in the middle looks essentially straight. 

 

I would have done this with flex track on the table, but I'm waiting for more track to arrive.

 

I'm never quite sure how much I need to worry about reverse curves. I know that in general they are considered bad, but at the same time, once the curve gets big enough, they stop being an issue. I'm just never sure where that big enough point is. 

 

Thanks for this reply, it's just what I needed.

 

J

[SZ]

As long as there is a straight longer than your longest vehicle there is no reverse curve.

[Keith Addenbrooke]

 

In case it helps, this is H0e - the far module is slightly longer at 0.9m but gives an indication of the gentleness of the S-curve over a similar displacement (the roadbed allows me to sharpen the curve a bit more if I want).   The 90 degree turn at the right hand end is Setrack 228mm / 9” radius for reference, and the risers bring the roadbed about 40mm above the frame.

 

I’m not aware of any H0e rolling stock / couplings that would have a problem with your S-curve, and running speeds are generally slow enough to help mitigate problems anyway.  Hope that helps, Keith.

Edited April 8, 2022 by Keith Addenbrooke

[Nearholmer]

Bear in mind that narrow gauge railways were usually built to narrow gauges for good reasons, and one of the good reasons was the ability to handle relatively tight, and ever-changing, curvature, thereby reducing the cost of earthworks in hilly areas by either “running the contours” or following the lie of the land to climb between contours. In hilly areas, such lines can squiggle about.

 

 

Slow speed lines, notably many that didn’t carry passenger traffic, were quite happy to use “train set” curves with no transitional curvature, but they did put one vehicle-length of tangent between reversals. This becomes very obvious on properly laid-out field railways, where spacing between parallel tracks at passing loops looks “too wide” at first glance, because the turnout is followed by a standard-length straight panel before the curve to bring tracks parallel.

 

 

 

 

Edited November 29, 2021 by Nearholmer

[St Enodoc]

19 hours ago, Harlequin said:

A 150mm straight in the middle would guarantee no reverse curve issues with your stock if you were really paranoid about it.

 

17 hours ago, Julia said:

I'm never quite sure how much I need to worry about reverse curves.

 

17 hours ago, SZ said:

As long as there is a straight longer than your longest vehicle there is no reverse curve.

In an ideal world, all curves (reverse and otherwise) would begin and end in a transition. We're not in an ideal world, so a) making the radius as large as possible and b) having a short length of straight in the middle of the reverse curve will stop you having any problems. The straight part doesn't need to be very long - the maximum distance between bogie centres would be more than enough.