Whilst out on a walk with the family I spotted this Railway tunnel vent above the tunnel on the GWR main line and took some photos, when I got home I started thinking about how I could draw this and also thought it would be good to have a modular design that you could look down through on your railway to see the trains going through the tunnel.

The vent I spotted was about 3m high with a metal railing around the top, I presume the railings were added in recent times so two designs will be needed for this. Also having a Google search these vents can also be found in built-up areas but are generally a lot taller above ground.

With all this in mind, I decided to create a 3m and 6m high version and I have created a design for the metal security fence. The internal diameter of the vent is about 3.6m. In OO scale this is about 40mm and 80mm high with an internal diameter of 48mm (approximately 54mm external diameter). I have created two heights for above ground so when printed there is no join when printing a taller vent.

So that you can model the vent underground down to the railway lines I have added 2 sizes of extension 38mm and 76mm, there are locating pins to join the sections together. Once printed and joined together there will be a brick effect down the internal wall of the vent.

This has been designed at OO Gauge, 1:76.2 Scale,For HO Gauge print at 87%, 1/87 Scale,For O Gauge UK print at 175%, 1/43.5 scale (You will need a large printer),For O Gauge International print at 158%, 1/48 scale (You will need a large printer),For N Gauge UK print at 51.5%, 1/148 Scale, (I have printed this in N scale and it prints fine).

Examples in the photos were printed on an AnyCubic Photon M3 Resin Printer

I recommend printing these items on a 3D resin printer to get the best resolution print, for larger scales you might be able to print them on a filament printer (Not tested). As per normal with my designs, there is a balance between accuracy and printability, hopefully not affecting the design of the model too much.Files starting with _ have supports added.