7 ¼” GAUGE SHAY LOCOMOTIVE.
Some notes on the basic dimensions and some constructional details
1. GENERAL.
Mainline gauge model, i.e. 1/8 scale.
Based on Lima “B” Class Shay, of about 65 tons, of early 1900’s
Overall size, 65” long, 14.5” wide and 20” high.
Dry weight is about 280 lbs, ( ~ 300 lbs working).
Project was started in May 2005, engine first run, without cab etc, in July 2007.
Model is not quite complete, needs domes, bell, pinion guards etc etc.
2. DESIGN.
Aim was to produce a loco which would travel easily at 5 to 6 mph and thus be
suitable for passenger hauling on Club tracks.(That is real, not scale speed).
The overall size and weight had to be compatible with my estate car.
It is thus my own design, based on information from books and the Web,
mostly USA based sites.
Was designed to be easy to operate and maintain, as far as possible.
Designed on a PC with a 2D CAD system, “Turbocad” v4.
Some attention was paid to lubrication methods, and replaceable bearing bushes.
Design of individual parts was made compatible with my machining facilities.
Note that the design is in metric dimensions, I have quoted inches here when
convenient.
3. SUB ASSEMBLIES.
Boiler
Copper boiler, coal fired, of conventional locomotive type, 100 psi rated.
Barrel 6” diameter, 17” long, firegrate 6” x 4.5”.
16 fluetubes and 4 super heater flues with stainless steel radiant type elements.
- I had the boiler made professionally.
Water feed is by rear truck mounted axle pump, injector or Wier pump.
Engine
3 cylinder, piston valve, Stephenson’s valve gear.
Scaled from full size 11” bore by 12” stroke engine, ie 36mm x 38mm.
Pistons are aluminium alloy with two cast iron rings.
Piston valve bore is 18mm, using 3 part stainless steel bobbins with cast iron
rings.
The 3 throw crankshaft is of built up construction, Loctite(603) and pinned, with
case hardened big end journals. The 3/4” diameter shaft runs in bronze bearings,
the centre ones being split.
The central eccentric pair is also split.
All the engine casings are to my design, cast by a local commercial foundry in
spheroidal graphite iron, (a ductile grade and beautiful to machine!).
Note: I am aware that all the early engines were slide valve, but I wanted a loco
that would not be an unwelcome slowcoach on the track, so I designed an engine
that would rev freely. It needs ~800rpm do travel at 6mph (model velocity), which
it does comfortably.
I understand some early locos were re-engined if they got damaged.
Trucks
Based on the early bar frame design.
Bar frame section 14 x 5mm black bar, 12 x 3mm for top braces, bottom angles
12 x 12 x 3mm.
Wheel diameter 116mm, (~ 4.5”). These are commercial front bogie wheel
castings for a 7 ¼” Gauge “King” class GWR 4-6-2 locomotive!
Gear ratio is 1.75:1, a bit lower than most Shays, (it also made the pinion
manufacture a bit easier). Gears are 35T and 20T, which I cut myself.
I made the patterns for the truck castings, cast as for engine parts.
The axles run in two-row self aligning ball bearings on the gear side, and a
standard sealed ball race on the other end in the sprung axle box, both 12mm bore.
The pinion shaft runs in porous bronze bearing bushes.
The truck pivots on a ball thrust race (slightly preloaded) with limit stops to
prevent damage to the universal joints etc in the case of a derailment.
Universal joints and sliding shafts much as Mr Shay designed them, shafts are ½”
square, sockets are two pieces of bright steel angle silver soldered together.
Cast iron brakes shoes on both trucks, chassis mounted vacuum actuator for front
truck, (to be compatible with most UK passenger stock), steam power cylinder for
the rear truck coupled with screw down cab handbrake.
Chassis
Main rails 20 x 40 mm hot rolled channel (single piece) with substantial plate and
channel drag boxes for the “Railroad Warehouse” couplers, (very nice), and one
channel frame stretcher.
The truck pivot bearing housing plate bolts to the side channels to allow easy
removal of a truck without any other loco dismantling.
Oak buffer beams of 26 x 40mm section complete the chassis.
Cab
Outline based on the early loco type, with typical Shay features.
Designed to lift off after removal of securing nuts to cab floorplate for easy
maintenance access to cab pipework and controls.
Removable cab roof section for ease of driving.
All timber construction in fine grained pine,(ex 1970’s window frame!)
Timber has been varnished, I have no idea what the full size did, but it looks
nice!
Front windows hinge open, side windows slide, both with hardwood frames and
Perspex panes.
The internal arrangement of controls has been made to make driving as
comfortable as possible.
Water tank
Outline based on the early loco type, with typical Shay rivet patterns.
Standard construction of sheet and small section angle, riveted together.
Sides fixed to floorplate to make a removable sub assembly.
Capacity nearly two gallons (UK).