All pointwork consists of up to three basic elements, namely the switch, the common crossing and the obtuse crossing. A simple turnout has a pair of switches and a common crossing, while a diamond crossing has a pair of common crossings and a pair of obtuse crossings. More complex pieces of trackwork are merely more elaborate combinations of the same three basic elements.

See also Turnout geometry, which describes the terms used for the various components and sets out the details of turnout geometry and their effects on modelling. This will help the modeller to decide on the degree of authenticity desired, bearing in mind the track and wheel standards adopted and the compromises that these require. To avoid problems when propelling stock, the tightest turnout radius on the layout should be 1.3 times greater than the minimum curve radius for the layout.

Turnout drawings and curve templates may be available from suppliers. Do a product search for Railway infrastructure and Trackwork. These generally cover a limited range of radii and crossing angles, albeit those judged to be the most popular. They offer the simplest approach but do not cover less common turnout geometries.

When designing a track layout a greater degree of variety and flexibility can be obtained by drawing the pointwork to suit the location. For example, Figure 1 shows a complex junction being laid out at the manufacturer's works. It could be described either as a double junction leading to two single tracks or as a scissors crossover. The two tracks leading off to the left are quite sharp as they have continuous checkrails. Note also that the right hand track of the two has a continuous curve through the diamond and therefore its two crossing angles will not be equal. This would be difficult to reproduce using pre-printed turnout drawings.


Figure 1. Pointwork pre-assembled at manufacturer’s works prior to transfer to site (Balfour Beatty Rail Rail Track Ltd).)

To produce drawings to suit an equivalent model location would require them to be custom designed. For those with or having access to a computer, computer-generated drawings can be produced by suitable software: see [link]. This article is devoted to two hand-drawn methods, one using pre-cut templates and one from scratch. The use of templates may be simpler but is so flexible and able to detail with complex point formations. Even if the modeller is using computer software, it may be of interest to study this article for the background it gives into point design.

For construction purposes, simple pointwork drawings using a single line to represent each rail are quite adequate. They can be drawn either by use of a ruler and pre-cut templates or by marking off a series of dimensions derived from the prototype and listed in the data sheet tables. The latter method literally becomes a process of joining the dots using a flexible drawing guide obtainable from most stationers. Although a reasonable degree of accuracy is desirable when drawing the outline of a turnout, its main purpose is to serve as guide to the shape and location of the components during assembly. The success of a custom-built turnout depends on the accuracy of the actual components.

The drawing is produced on a sheet of paper large enough to accommodate the complete turnout. While it is possible to draw turnouts directly onto the track base, clearer definition and greater accuracy can be achieved on paper. Where more complex track layouts are involved, it is advantageous to draw the complete configuration. Decorator’s lining paper is a cheap yet effective medium since, by using a length off the roll, the adjacent trackwork can also be drawn in. The preliminary drawing can be sketched out in pencil to obtain the best track layout but, for clarity and permanence of line during construction, it is recommended that ink be used for the final drawing.

When it is finished, the drawing can be divided into suitable sections for construction on the workbench. Generally, construction on the workbench is preferred over construction on the baseboard with the track built in situ, but if the baseboard is to be a solid construction, the paper can be fixed to the baseboard and the track built over it.

Some time may be saved if master drawings of switch and crossing units are made on tracing paper or on transparent sheet. These can be copied, the copies placed in position and the rest of the turnout then drawn in. By using tracing paper, only one hand need be drawn, the opposite hand being obtained by reversing the tracing in the copier.

Some suppliers offer curve templates, often cut to a high degree of accuracy to 32mm or 33mm gauge. The radii, quoted to the centre line, reflect those most popular with modellers, which are not always scale equivalents of full size configurations. Some close correlation is often possible but, where a non-standard crossing angle would result, the insertion of a suitable straight length before the crossing to correct the crossing angle is a solution. The three types of switch: straight, semi-curved and fully curved. The simplest turnout to draw is one having straight switches, either of the tongue or the heel type.

The illustrations in Straight switches also show the location of the timbers and slide chairs in the switch area. Select a suitable switch length to suit the turnout radius. Suggested lengths are given for different turnout radii in Tables 1 and 2.

Table 1. Straight switch lengths suitable for turnouts of different radii.

Table 2. Model switch length for a given prototype switch length

¹ Assuming either code 124 bullhead rail or code 143 flat bottomed rail, having a rail head width (hr) of 1.6mm.
² Assuming either code 200 bullhead rail or code 220 flat bottomed rail, having a rail head width (hr) of 2.35mm.
³ These switches have a significant angle of deflection at the toe and should only be used where limited space prevents the use of longer turnouts.


Measuring and marking off the small distances involved directly on the drawing is not easy so the following method should make the task simpler when setting out the drawing.

a) Draw the gauge lines and mark the position of the toe of the turnout (T), Figure 2.


Figure 2. Setting out the heel for a straight switch.

b) For the appropriate standard and teh chosen switch length, mark off a length along the straight stock rail equal to 10a, where a is the switch angle ratio (1 in a) at a point A. Through A draw a line at right angles to TA and mark a point B, 10mm from A. Join BT and mark TH equal to the switch length LH. Check that the heel divergence (hd) from the stock rail is:

• Scale 7 - 2.62mm
• O Fine - 3.35mm
• O Coarse - 3.8mm
• O Coarse - 4.55mm

c) Either place the curved template against the point H and judge by eye when it forms a tangent to the switch rail TB (Figure 3 inset), or, from the switch heel H measure along the switch rail angle line a distance of 200mm. (It may be necessary to extend it to do this). Draw a line at right angles. Mark off an offset distance O selected from Table 3 to suit the turnout radius. (If the curve radius is not shown in Table 3 it can be calculated using the method in Turnout geometry).

d) Place the curved template against the points H and O and draw the curved closure rail, extending it until it cuts the other rail at the gauge intersection.

Table 3. Closure rail radius and offset for various curve radii

Figure 3. Setting out the curved closure rail.

e) The turnout curve can continue through the crossing as shown in Figure 4 by position 1. However, if the turnout forms part of a crossover, to avoid buffer locking, the Vee should be straight from the crossing nose as shown by dotted line 2.


Figure 4. Crossing variants.

f) If the crossing angle is an odd figure, a standard angle can be drawn in as shown by line 3. This is drawn tangential to the closure rail curve and will increase the full lead of the turnout by a small amount.

g) The straight gauge lines were drawn at the beginning. Along these draw a line at right angles at a distance of 38 mm (5ft 5in.) in front of the switch toe. This is the forward end of both stock rails. (Note that some pre-group companies used a shorter length and the relevant data should be consulted for verification.)

h) If using a prepared switch drawing, then the portion of the curved stock rail adjacent to the switch planing can be traced from it. If not, it can be prepared from b) above. Mark the position of the toe and draw a straight line parallel to TH, the curved route switch, and measure a distance equal to the switch length. The stock rail curve commences at this position opposite the heel of the straight switch; see also Figure 9 in basic turnout construction.

i) Draw the stock rail curve by plotting a number of points at gauge distance from the curved closure rail and joining up. Absolute accuracy here is not essential since when laying the stock rail, it will be gauged from the curved closure rail.

Since the switch radius of the A semi-curved switch equates to 3380mm (11ft 1in) in 7mm scale and that of the B semi-curved switch to 4295mm (14ft 1in), it is unlikely that a suitable commercial template will be available and therefore the preparation of drawings for semi-curved switches is better undertaken by the offset method described below.

For a fully curved switch the template is positioned at the toe so as to be tangential to the gauge lines at that point. In this case, as in step c) above, the offset to the point O, is measured along the straight stock rail from the toe T. The inner and outer curved gauge lines are then simply drawn, with the template as a guide, to a point beyond the gauge intersection. The result is a fully curved turnout, although neither turnout radius nor crossing angle will necessarily be standard. This is the type of switch recommended for O coarse if code 200/220 rail is used (see Turnout geometry).

The sequence is to draw the switch followed by the crossing and, finally, by the turnout curve. See Turnout geometry and also follow the links there for each component. If a straight switch is to be used, the procedures described above using templates should be followed.

a) Commence by drawing the gauge lines and marking the position of the toe of the turnout T (Figure 5). Having selected the type of switch to be drawn, from T measure a distance TX taken from the Table 4. This is the point where the switch angle line cuts the straight gauge line. Measure a second distance TY and draw a line at right angles to the straight gauge line at Y. Mark a point Z, 10mm from Y and join ZX. The line forms a tangent to both switch and turnout curves.

Table 4. Dimensions TX and TY.

Figure 5. Setting out the heel and drawing a curved switch.

b) Measure the heel distance LH and draw another line at right angles to the gauge lines. Where this line cuts the XZ line is the heel of the switch. Check that the heel divergence dimension, (HD), agrees with those for the relevant swtch type: straight.semi-curved or fully curved. The point H thus marked lies on the switch curve.

c) For curved switches only from the data tables, select a number of intermediate switch curve offsets and plot these in the same way. The switch curve can now be drawn by joining up the plotted points.

d) For semi-curved switches the planed length is straight, the curve commencing at the end of the planing (Figure 6). This requires a second triangle to be drawn using a similar method. Mark off TQ from the table in the figure and at Q draw a perpendicular to the straight gauge line 10mm long to R. Join TR. Mark TP, the planed length, and draw another perpendicular PS. This is equal to the rail head width hr. The switch curve is tangential at S and H. e) The curved stock rail can be drawn either by repeating the foregoing procedure or by marking the gauge distance from the points already plotted.


Figure 6. Setting out the heel and drawing a semi-curved switch.

Once the switch is drawn in, the turnout curve can then be added, Figure 7.


Figure 7. Setting out the turnout curve using offsets.

f) Obtain the distance L from toe T to gauge intersection I from the appropriate closure rail data sheet and, through I, draw a line at right angles to the straight gauge lines.

g) Through the point of intersection I draw a line inclined to the straight gauge line by the crossing angle. (If a straight crossing is being used then mark a point S along this line towards the toe equal to the straight length required). The technique used to draw the straight switch can be used here to draw the crossing. Measure 10b along the gauge line and project 10mm to give a point on the line through I at 1 in b. (Example: measure 50mm along the gauge line to give a crossing of 1 in 5).

h) Draw a straight line from I to H (or S to H) and mark the ¼, ½ and ¾ positions along it, drawing a line at right angles to IH (or IS) through each.

i) Along the mid-point line, mark the offset V₂, obtained from the data tables and along the ¼ and ¾ lines mark the offsets V₁ and V₃ respectively. These are both 0.75V₂.

j) The turnout curve passes through the three offset points and is tangential to the lines through points H and I (or S). It can be drawn in using a draughtsman's flexible curve or similar.

k) The crossing angle has already been drawn in at h) and the next stage is to mark the crossing nose. The nose N is set back 0.44β mm behind I, the crossing intersection, for a crossing angle 1 in β.

l) The neck in the wing rail is found by marking a point at a distance β x F_y from I towards the toe along the gauge lines (F_y is the flangeway width for the standard being modelled and forms the base of a triangle, the long side of which is the distance from the gauge intersection to the neck).

m) For Scaleseven, prototype wing rail dimensions can be used, but for both fine and coarse O, although the overall length is unchanged, due to the greater flangeway widths the neck has to be further away from I. See Crossing dimensions. The same technique is used to draw an obtuse crossing and dimensions are given in Obtuse crossing.

The drawing methods described so far assume that the turnout has the configuration of a curve leading out of a straight. Occasionally it is advantageous, and sometimes unavoidable, for the turnout to be a curve out of a curve. There are two variants depending on whether the two roads curve in the same direction or curve in the opposite direction. Either variant can be drawn using pre-cut templates as described above, but where the roads curve in the same direction, for O finescale the crossing angle should be limited to a mimnimum of 1 in 8 to avoid excessive drop in and very long leads. A rough guide is to ensure that the larger radius is a minimum of 1.5 times the radius of the diverging road (Figure 8). The end result could well produce non-standard crossing angles and switch lengths. Straight switches would not be suitable unless the radii involved were very large and outside the range usually modelled. Semi-curved and fully curved switches would suit most applications except where code 200/220 rail is used, where fully curved switches would be more suitable.


Figure 8. Minimum ratio between curves for a curved turnout.

When producing a drawing using the offset method it is necessary to determine the full lead and crossing angle. These are obtained using a very simple calculation known as the 'Principle of Equivalent Radius'. Simply, one route is regarded as straight and the equivalent radius is that which the other route would follow to give the same lead and crossing angle as the actual formation. Although the results are not strictly accurate, the mathematical error on the prototype is insignificant and is acceptable as the actual turnout radius is not critical in model form.

Let R_T1 and R_T2 be the turnout radii of the two routes with R_T1 being the larger radius. When both curves are in the same direction the equivalent turnout radius, R_TE, is:

R_TE = (R_T1 × R_T2)/(R_T1 − R_T2)

When both curves are in opposite directions, i.e. a wye turnout, R_TE can be found from:

R_TE = (R_T1 × R_T2)/(R_T1 + R_T2)

These formulae can be used in two ways. Where a preliminary design has been sketched they can be used to find the turnout with the best fit to suit the location. Alternatively, if a turnout with a known crossing angle is to be inserted into a curve, the radius of the second curve can be calculated. In the former case, when the equivalent radius has been calculated, consult the turnout curve data sheet of the appropriate modelling standard and find the nearest value of turnout radius R_T in the table. If there is not a precise match use the nearest value, preferably above, and use this as the equivalent radius, R_TE, and adjust R_T1 and/or R_T2 to make use of a standard crossing angle. The rest of the information can then be taken from the tables and the formation drawn using the larger curved stock rail as the base line.

See also Pointwork drawing examples.

These can be great space savers, especially in the limited space normally available to modellers. Drawing them is basically a matter of superimposing one turnout over another. Although two of the crossing angles can be specified, it is not always possible for the third to be a standard angle and it will need to be determined by drawing. It is strongly recommended that any three-way turnout be drawn as a tandem turnout and not as a three throw. Although feasible in Scale 7 it becomes more difficult in O fine and O coarse and can create problems in the construction stage. The tips of the inner and outer blades are staggered by approximately one sleeper centre distance (see Figures 4 and 5 in Prototype pointwork. Figure 9 shows the general layout. Moving the second turnout back avoids the need to stagger the blades and simplifies their operation in a model (Figure 10).


Figure 9. Stretcher bars shown to link the staggered blade toes of a 3-way turnout.


Figure 10. Tandem three-way turnout. Note that the second set of switch blades are located behind the heel of the first set. Note also the timbers square to the main road and the continuous check rails suggesting a curve of less than 10 chains radius (Howard Finch).

The timbering of the switches and crossings is determined by the switch type and crossing angle but practices varied between companies. Generally timbers were either set at right angles to the straight stock rail or, as in modern practice, progressively angled to form a right angle to a line through the crossing nose. With the exception of the four straight switches, the timber centrelines shown on for semi curved and fully curved switches are based on post group practice. See also the article on timbers (sleepers).

Most of the switches likely to be modelled have two stretcher bars, the first being 13in (7.6mm) from the switch toe with the second 3ft (21mm) beyond that. Modern stretchers are of 2.5in x 7/16in flat bar but many pre-group companies used a circular section; the Midland's, for example, having a diameter of 1¼in. In Photo 2.16 in Prototype pointwork the turnout has a very large radius and there are no feweer than four stretcher bars, the first forming part of the facing point lock, compared with the single stretcher bar in the sharp radius turnout shown in Figure 2 in Design of model pointwork.

For most modelling applications, the check rails will be 91mm in length and extend over the same five timbers as the wing rail, although there were variations between the companies. Generally, the check rail should be made 5mm longer than the wing rail, with the extra length at the closure rail end.

For bullhead track, 11mm at each end is bent to increase the prototype flangeway by 1mm, while for flat bottom rail, the lead into the check and wing rail is planed instead. To be strictly correct, the next 12.8mm of a bullhead check rail should be bent to a radius of 220mm, but most modellers will be content to merely bend the end.

Turnout geometry describes the terms used for the various components and sets out the details of the turnout geometry and its effect on modelling.

Turnout geometry calculations explains, with examples, the calculation method. This article is for modellers who wish to draw turnouts not covered in the tables, or those who wish to know how the information is derived.

Pointwork drawing examples contains several illustrative examples of the process of calculating the important dimensions for curved turnouts.

BS 4521: 1971 Specification for railway turnouts for private users - Part 1: Turnouts over which Bristish Railways locomotives operate - Section 1.1: Turnouts using BS9 section 95R bullhead rail - Section 1.2: Turnouts using BS11 section 110A flat bottom rail.

Contains many drawings of turnouts and turnout components. Later versions of this British Standard may omit Section 1.1.

This article was developed by M. Holland with additional material from R. Chown, H. Finch, G. Overton and K. Thomas for the Gauge O Guild Manual. It was adapted for the GOGWiki by Nick Baines.