Article: Making Smooth Curves

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Silver Surfer
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Article: Making Smooth Curves

Postby Silver Surfer » Wed May 24, 2006 1:26 pm

Laying Smooth Curves:

We’ve all been to exhibitions and seen those lovely sweeping curves on layouts wondering how they managed to make them so even and consistent very often with large radii. This article explains how you can achieve consistent good looking curves with an easy to make, inexpensive template.

Firstly, for those unsure of the terms, we need to know the difference between radius and diameter.
The Diameter of a circle is the measurement from one side of a circle to the other, taken at a point that crosses through the centre point.
The Radius is a measurement taken from the centre point to the outside edge (and is half the diameter).

You will need;-
1 x piece of stout card having a long straight edge, about 60cm (24”) x 20cm (8”)
1 x piece of string – 30cm (12”) longer than your desired radius.
5 x large drawing pins.
Scissors or a sharp craft knife.

Our first task is to scribe an arc along the face of the card equal to our desired radius and, as none of us own a compass that can deal with anything larger than a few centimetres, we have to come up with an alternative.
Tie a pencil to one end of the string. Measure the distance of your required radius and then suitably secure the other end by placing a heavy object on it or tying it to something. This may sound complicated, but it isn’t, and a little trial and error will soon have you drawing arcs of unmentionable sizes.

For example, Fig 1 shows a method of drawing large radius arcs by tying the string to a door knob, placing your card on a table across the room and, keeping the string taut, scribing the desired arc with the pencil. This is how I made a template with a radius 244cm (8’0”)


Fig 2 shows the card after scribing. You should cut away and discard the shaded portion. At this time it is an idea to write on the template the radius just scribed as, if you make several, you won’t remember which is which.


Now, having made our template, how do we use it. I find the following method best.

Connect your flexible track to the end of your last remaining fixed piece of track – usually a straight.
Place the template on your baseboard ensuring as far as possible you start with the straight edge of the template more or less parallel with the straight section of track you are extending (See ‘B’ in Fig 3). The beginning of your curve will line up approximately half way round the arc of your template. By starting with your template in this position you will ensure a nice gradual sweep onto the curve. Once you are happy with the position of the template, secure using the drawing pins. See Fig 3.


Note: I always pin down the first 5cm (2”) of the new piece of track I’m laying as a continuation of the straight (as at ‘A’ in Fig 3). If you start to bend the track immediately at the joint, the likely hood is you will suffer derailment problems later on as the effect will be similar to that in Fig 4 - (although not so pronounced).


Gradually ease the flexible track so that it butts up to the edge of your template and secure every 10cm (4”) or so. Work your way round fixing the track until you arrive at the end of the template. Lift the template and re-position snug against the curve you have already fixed. See Fig 5.


Continue round the curve until the desired length has been laid. Fig 6.


As you work round the curve, you will note that the outer rail ends up considerably shorter than the inner rail and it will be necessary at this point to crop the inner rail to equal that of the outer rail and also remove the excess sleepers.
I find by placing a square across the template and rail, as shown in Fig 7, I can mark the rails prior to cutting to ensure they line up nice and neatly with the next piece of flexible track.


Others will have their own ideas about laying smooth curves but this works for me. I hope this article helps you to avoid those awful looking fifty pence piece curves.


ps - you could also make these templates out of 3mm ply or mdf for a more substantial and long lasting product...

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