GME news

The first GME bridge to be sold (a PL24) was sold by Winona Garden Railway of Guelph, Ontario, in November 2009, and since then they have travelled around the world, mostly to the USA, but also to Türkiye, the Czech Republic, the UK, Anguilla, and Tasmania. Production quantities have been small, but they have found a niche with people who like the real rivets and the fact that they are built by hand. Some have been specials designed to the customer's requirements, and many others have been modified standard designs. In fact, shipping a standard bridge has been a rare event.

After thirteen years and hundreds of thousands of rivets, a few complete bridges - all specials in various ways - are still available. At the moment there are:

- One 0/S scale 24" operating bascule bridge

 

- One PL24 medium width plate girder bridge

 

- One TR 42 deck truss with timber deck, 45 mm gauge track, and handrails.

We are still pleased to answer general bridge questions and will supply outline drawings of the GME bridges for people who may find them helpful with their own designs.

Gnome on show

We spent an enjoyable day at the 2023 Ontario Narrow Gauge Show  on 15th April in Hamilton, Ontario, after a long break for the pandemic, and had the last few GME bridges on display there - all specials of various kinds. As always, it was a fine show of imagination and craftsmanship, in an excellent location, and with plenty of interested and interesting visitors.

0 and S scale bascule bridges

The BA24 bascule bridge for 0 and S scales is an operating trunnion type with an opening of just over 18 inches (457 mm).  It is a balanced design using a cast concrete counterweight. It can be supplied for either manual or remote electrical operation using a DC gearmotor and chain drive with a torque limiting clutch. One powered bridge assembly is still available.

O, Gauge 1 and G scale plate girder bridges

Click on the drawing below to see a larger version:

Standard plate girder lengths:
Model no.   PL12     12 inches (305mm)
                   PL24     24 inches (610mm)
                   PL36     36 inches (914mm).
Widths: 
                                 4 inches (102 mm)
                                 2.54 inches (64.5 mm)
                                 2.0 inches (51 mm).

(Above) PL12M for 1:20.3 scale

(Below) Rivet detail

G scale and Gauge 1 truss bridges

These are available in three widths as deck trusses for the larger scales, with the timber deck included. The standard lengths are shown above, and others may still be available to special order. An example of the narrowest version of the TR42 with two PL36 plate girders, is shown below. This is 114 inches (2.9m) overall, and assembled with 1,274 solid rivets. Watch an animation of a customer's installation.

Through trusses for 0 and S scale

Extra height TR32 (32 inch span) trusses for 0 and S scales, with increased internal clearance for North American double stack container cars, have been built in single (TR32H) and double track (TR32DH) configurations. 

Frank Grantham 1933 - 2018

We are saddened to record the death of Frank Grantham, a mechanical designer par excellence, who was one of the original partners in GME. He was responsible for the detail design of the basic structures of a series of bridges that continue to be shipped around the world, from Canada to Tasmania. Frank had served a craft apprenticeship in the UK, and we knew each other first as colleagues at a Canadian company building naval aircraft handling equipment. Following his retirement he helped set up Gnome Miniature Engineering, combining professions and hobbies. Always a fine designer, a meticulous model maker, a good friend and a most congenial colleague, he will be missed.

How they are made

For the standard structures, each part is laser cut from aluminium alloy sheet, cleaned, deburred, brake-pressed, joggled if required, and then riveted into the assembly using solid rivets. Here is a plate girder rib as cut and after forming:

Parts are often altered from standard to suit particular variants, and this is mostly done by hand.

Below is a sub-assembly of an all steel custom bridge that went to a client in Türkiye to display his 1:8 scale live steam locomotive (see bottom of the page):

Custom bridges

A large proportion of our work has been to special requirements, such as this 1:8 scale steel static display bridge - a favourite project that went to Istanbul. It incorporated 7 1/4 inch gauge track parts from The Miniature Railway Supply Co.

































The most economical approach to a custom design is to base it on standard parts. The picture below shows the first of many specials; this one for a large 0n30 railway, using mostly modified standard parts.

Masonry viaducts appearing to be curved are common, but there was rarely a horizontally curved steel bridge until the development of modern welded box girders. Most bridges that appear to be curved are a series of straight sections, and this is how we build a curved bridge. For a sharply curved bridge, the girders will be trapezoidal in plan, as in the example for an 0n30 railway shown here.

Decks

Prices include timber decks consisting of transverse timbers with longitudinal guard timbers. Assembly is with nails, and screwed cleats secure the deck to the structure.

0 and S scale decks for indoor use are from precision milled basswood sections from Mount Albert Scale Lumber, either stained to resemble fresh creosote or with a simulated weathered appearance.

This illustrations show four different red cedar outdoor decks after weathering for up to six years.

(above) L-R: (1) pictured after 6 years exposure, no stain, no preservative; (2) 6 years, stain with preservative; (3) 5 years, stain with preservative;  (4) 3 years, stain with preservative. They are exposed to sun, rain, snow, salt, cats, deer, raccoons, squirrels and birds. After 7 years exposure, the specimen on the left appealed so much to a customer that he asked for it to be installed on his TR42M. Happy to oblige! Properly drained, the cedar weathers well and keeps its strength.

The standard large scale decks are red cedar, stained or unstained. For Gauge '1' the transverse timbers are 5 inches (127 mm) and for 'G' they are 6.4 inches (162 mm) long, corresponding to roughly 13 feet (3,962 mm).

Prices and availability

Series production of the GME bridges has ended, but several complete bridges remain available for sale. Please e-mail us at gme@gnomengineers.com for the prices and availability of the bridges shown in the News post above.

Gnomes...

If you arrived here looking for gnomes, we have to say that's just the name, not the product. However, we are happy to recommend a friend in the gnome business deep in the Muskoka forests of Ontario, who will make the most delightful gnomes in all shapes and sizes for you.

Individual girders

Individual plate girders to add to your structures are available in 12, 24 and 36 inch and intermediate lengths (305, 610 and 914 mm).  A 1/2"x 1/2"  mounting angle is riveted to the inside, and stainless steel screws are provided for attaching the girders to your own deck.

These girders can be packed more compactly than complete bridges, substantially reducing shipping costs.

Paint

The most popular paint finish is flat black, but red oxide, grey primer, or unpainted finish are also available. All structural materials and fasteners are corrosion resistant, so the bare metal is always satisfactory outdoors.  Unpainted bridges are cleaned before delivery, but customers who paint their bridges should ensure that the surface is clean and dry before painting - wash them in a strong detergent followed by thorough rinsing and drying. Use a primer formulated for aluminium alloy surfaces and allow ample drying time in a warm, dry environment before top coating.

Bridge strength and stiffness

GME bridges are certainly quite light...

But they are strong...

The original design specification said there must be negligible deflection with a 25 lb (11 kg) locomotive at the middle of the longest span. The picture shows about 74 lb (34 kg) of bricks stacked at the middle of a TR42 with negligible deflection.

A knitted bridge

Nothing to do with GME this time, but here is the Main Street Bridge in Cambridge, Ontario; normally just an unattractive mass of Depression era concrete with a false bowstring girder superstructure. However, for a few weeks in autumn 2010, it was transformed by hundreds of local residents into a lively and colourful collage of knitted items of all kinds, celebrating the town's history in the textile industry.

Track

The bridge decks are designed to accept the popular makes of prefabricated track, such as Aristocraft and LGB for 45 mm gauge, and Peco, Atlas, Gargraves and older Lionel for 32 mm. Guard timbers are provided on all decks, and the track fits between them. For a more prototypical appearance, the rails can be chaired or spiked directly to the deck cross timbers.

Note: If you use Lionel Fastrack, please let us know before you order. Single track through trusses may need some adjustment to the deck, but double track through trusses are not suitable if 6 inch track centre spacing is used.