Last updated on
21st March 2020
The 3½"and 5" gauge track is constructed of mild
steel flat 3/4" x 3/8" (20mm x 10mm) on edge.
Originally the rail was supported by bent
16swg mild steel chairs 1" wide, riveted into
the rail with 3/16" soft iron rivets and either
fastened to wooden sleepers by 1" x 12 mild
steel counter-sunk screws. The sleepers were
made out of any suitably treated wood although
the majority are hardwood, and have a minimum
dimension of 11" x 1 ¼" x 7/8". The
sleeper spacing is every 10 to 13" depending on
the location. Rails were joined using angle iron
fishplates bolted to the rail.
As and when sections of track have had to be
renewed the rails have been welded to metal
sleepers. The metal sleepers were often
made by cutting up the old rail that was being
replaced. Rail joints are now also welded. There
are now only a few sections of track that are of
the original construction.
Track foundations are concrete, to a minimum depth of
15" with a surface width of at least 12".
A 4" soil pipe is buried alongside the track to
convey cables and air lines around the site.
The wooden sleepers of the track rest directly
on the concrete. Where steel sleepers are used,
these will normally rest on an unattached wooden
sleeper below. This gives sufficient clearance
below the rail for the concrete foundations to
be covered by granite chippings to give a
As with the track itself there has been a significant change from the original
method of construction. Originally bricks were let into the ground at regular
intervals and the sleepers rested on these. This quickly gave rise to problems
maintaining accurate track levels and so work to place the original main line on
concrete foundations was undertaken in the 1970s. All subsequent extensions were
built with concrete foundations from the outset.
The minimum curve radius is 29ft in the steaming bay
loop and 37 ft on the main line. There is an 18 ft transitional curve length on
the outer main for a straight to a curve. The super-elevation design speed on
the outer main is 6 mph (10 kph) with a maximum cant of 3.6° on the curve, cant being at a rate of 0.2° per ft.
The concrete track sections were
levelled to the appropriate track cant when laid in the late 1970s. The cant
effect was not found noticeable so when the inner main was laid in the 1990s
super-elevation was not used. The 3½" and 5" gauge tracks have a common outer rail
and a minimum structure gauge of 3ft wide by 4ft 6ins high.
The original points on the railway were of the stub type, where a whole section
of track slid sideways to line up with the other track. These have now all been
replaced by points of more conventional design and the points are now of all welded construction.
The majority are operated by compressed air, but two, giving access to sidings, are
operated by hand as required.