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Track   

Even with no trains running on a Broad Gauge layout, a noticable component is likley to be the seeming chasm between the rails of a scaled 7 ft gauge track, so this is worth the effort to look right.

This image of mixed gauge tracks is quite a different look from today's cross sleepered track, and clearly shows the drainage cess between the running rails.

Making Baulk Road track in 7mm scale


The Prototype

Brunel's unique broad gauge trackwork was formed of 14" by 7" timber baulks laid longitudinally, originally fastened to the tops of round wood piles.  Wider baulks were used at points and crossings.  Cross ties (transoms) of 5" by 7" timber were positioned every 10ft, with iron tie bars fastened through the width of the baulks, positioned just to one side of the transoms.  Ballast was laid above baulk level initially; later, just level with the top of the baulk.  However, after a while, the baulks sagged between the piles, so the piles were removed, and the whole track was supported by the ballast.

                                          
The iron 'Bridge rail' was supplied in straight sections, 15 ft in length, and fastened down with bolts through the flange on alternating sides, at about 18 inch intervals.  No curved baulks (or rails) were used on the prototype, and the radii of bends varied from 500 to 1000 ft.  In the early days, the rail was laid on top of a wedge layer of cross laid 1" thick, 6" by 8" hardwood or pine packing, on top of the baulk.  This canted the rails inward, so the wheels tyres would run flat on the rail; but was later discontinued as the slightly tapered wheels naturally centre the axle on the rails.

Over the years the 'weight per foot' of rail increased to cope with heavier locomotives and trains; and in the final years new broad or mixed-gauge track was being laid on cross-sleepers, as on the narrow gauge parts of the GWR network, with bull-head or flat-bottomed rails.  Bull-head rails in chairs particularly eased the final gauge conversion.

Away from stations and yards, a central drainage gulley was created between the rails, by raking the ballast to each side to support the baulk, and the transoms formed a distinct bridge over the gulley (cess).  However, in yards where horse and man shunting took place, setts or cobbles were laid between baulks, at baulk level.

A full size bend of 500ft radius is 3.5m in 7mm scale, and modellers normally do not have that sort of space.  One solution is to only model straight-ish track, as in 'Bristol Goods Shed' (as photo).  The 'Coldrennick Road' layout uses 4ft 6ins (1.32m) radius, but gauge widening of up to 49.7mm is essential for such curves.  Other railway builders use 6ft (1.83m) - a recommended minimum - and 8ft (2.44m) where space allows.  Rolling stock can be engineered to tolerate these curves, 6 wheelers and rigid wheel base locomotives needing lateral slack for middle axles and coupling rods, but that's a whole new topic !

The Model Baulks

Bass wood or hard wood of oblong section is ideal, and can be fastened down with screws or wood glue; 8mm by 4mm for baulks, and 3mm by 4mm for transoms.  Careful measurement of the position is required so that when gauged, the rails sit centrally on the baulks.

                                          
If you are ballasting up to baulk level, or modelling track with setts laid between, you can use thin ply baulks, such as the pieces supplied for scratch built points, 8mm wide.  With Nickel Silver rail you can use copper clad PCB strip (see later).  A good supply of ready cut timbers of all sizes and woods can be found in the marine modelling world, per metre lengths.

You can model the iron tie bars with straight wire, painted black, positioned just behind the cross ties, with a bolt head on the outside of the baulk, or drill through and push the wire through to simulate the bolt heads.

The under rail packing can be modelled with 5mm wide strips of card, the planks indicated by scored lines.  The strips can be glued down to the wooden baulks and painted, as on 'Teign House Sidings', but sensibly, most people leave the packing out - and unfortunately it isolates the rail from copper clad PCB baulks.  Similarly, the baulks should be painted and weathered - black for new creosote, varying browns for weathering.

Bolt heads can be glued to the top of the flange - again, most people leave this out, but Paul Marchese laboriously created them all with blobs of araldite on 'Baker Street'.  They can also be seen in the above photo of the display track made by Bill Saltau.

Victorian era ballast was perhaps a little finer than the aggregates used today.  In the photo of the display track, standard model railway ballast has been used, similar to that sold by Peco and other suppliers for 4mm scale track.

The Model Rails

There are two types of 7mm scale Bridge Rail available - Aluminium and Nickel Silver - but only one weight of rail, the later, heavier type.  Nickel Silver can be soldered with ordinary solders and an iron, but it is not easy to solder or weld wire to Aluminium.  It is best not to try, but to find an alternative method.  Aluminium rail is a tenth of the price of NS, but many of the lengths have a slight twist which can cause difficulties.

                                          
The rail has a good flat bottom flange, which lends itself to fixing down with glue.  PVA or Araldite have a long set period, so the gauge can be adjusted before it sets.  Keep a weight on the rail until the glue is set.  Superglue is instant but more permanent than PVA, and is suitable for quick repairs, especially if the original fixing was with Araldite.  The Araldite forms a slight channel, which helps to keep the track to gauge as the rail is pushed back down into the superglue.  Glue gives an invisible fixing.  If you don't trust glue, see below.

Other fixing methods and electrical connection - NS Rail

Since you can easily solder copper, brass and NS to NS, you can solder it down to copper clad baulks, but there are caveats.  Watch out for distortion as heated metal expands.  Unless you are good at sweated solder joints, excess solder will be apparent around the flange.  Electrical connection can be made by soldering wire to the outside of the rail and leading down below through a hole in the baulk.  This is most suitable to yards and stations where the ballast and setts can hide the joints.  If you are modelling rail bolts (as above) you can use the wire as an electrical connection which can go right through the baulk to wire underneath baulk or baseboard.

Alternatively, you can solder the flat head of a countersunk bolt underneath the rail and lead this through a hole in the baulk, out of sight, and make electrical connection using nuts and a solder tag under the base board.  If two or more bolts are used in this way, they can be an alternative fixing to glue.  Watch out for little nuts becoming loose in transit on exhibition layouts.

Other fixing methods and electrical connection - Aluminium Rail

Instead of soldering bolts to the rail, you can drill a very small hole from underneath, and tap it out to take a thin brass bolt.  This has to be 14BA or 12BA; any larger and you can damage the rail and see it from above.  A solder tag, with a length of wire, and nut at the head of the bolt before inserting gives electrical connection, and the hole in the baulk and baseboard should be wide enough for the rail to be lowered into position and not too wide to be hidden by the rail flange.  It is best to make a drilling jig that centres the drill over the rail flange, so each hit is correct.  Only one connection is required per length of rail.  There is some concern about dissimilar metals reacting with one another, brass and aluminium being especially reactive, in the presence of water.  Layouts kept in normal dry domestic conditions should have little problem.  A prominent 7mm modeller has had at least 15 years' operation without any sign of corrosion.  If you are concerned about this, consider using steel bolts.

This drilled and tapped hole and bolt is unsuitable for fixing the rail in position - you must use glue of some form for this.  I have found PVA is a good fixing as long as you don't give the rail a jolt, or catch it with your sleeve and pull it off.  It is also excellent for track repairs and re-alignment as it will give way with a screwdriver blade twisted under the rail.  Araldite and superglue will hold tighter to the rail.

Bob Harper on 'Maristow' layout used aluminium rails glued to wood baulks.  The electrical connections were made by forcing a steel dressmaking pin down through an interference hole in the web, and coating over the top of the pin with conductive paint; the wire feed was then soldered to the bottom of the pin.  He had a good thirty year life from it, but recently has had to remake these, using the same connections, by drilling down through the head of the rail, and forcing in a wire dropper with a wider, tapered top down through the hole before filing flush.

Happy track laying !         -    Pete Boyce