When I was designing this set of designs I was doing it for my Model Railway Club and there was a clear need for the ability to have two tunnels next to each other in some circumstances. As these tunnels could be various distances apart then I also needed various sizes between buttresses. On railways with embankments there is often supporting walls either side of the tunnel portal and this can be achieved with this add-on.

Within this add-on there is a joining buttress with groves on both sides to slot portals and extension walls in. The extension adds approximately 6mm of width to the wall face. The extension walls come in four sizes of 30mm, 60mm, 90mm and 120mm with 6mm at each end that slots into the buttresses. These walls are the same height as the portals at 116mm tall and the extension buttress is approximately 125mm tall.

Whilst researching this design I found that tunnels come in so many different forms, and the surrounding support walls also come in lots of different arrangements. Therefore, as I develop this design, I will be adding several add-on components to help with building tunnels and bridges. (I am starting this project in April 2025 and will add components going into the summer of 2025.) I am also adding a single-track portal and add-ons.

The add-on components I’m looking at adding are:

Tunnel Portal Fronts (Single and Double) https://www.cgtrader.com/3d-print-models/games-toys/other/model-railway-tunnel-portal-double-track-modular-design https://www.cgtrader.com/3d-print-models/games-toys/other/model-railway-tunnel-portal-single-track-modular-design

Curved internal Arches will be made up of 2 degree and 6 degree segments, can also be formed with other arch sections to form exactly what you need that is not 2nd, 3rd or 4th radius.

designed at OO gauge, 1/76.2 scale but can easily be scaled for other gauges.for HO gauge print at 87%, 1/87 Scale,for TT print at 63.5% 1/120 Scale,for O gauge UK at 175%, 1/43.5 Scale,for O gauge International print at 158%, 1/48 Scale,for N gauge print at 51.49%, 1/148 Scale

The examples in the pictures were printed on a Bambu Labs A1 FDM Printer.As normal with my designs, there is a balance between accuracy and printability, hopefully not affecting the look of the model too much.

For FDM printing, I used a 0.4mm nozzle and a layer height of 0.12mm using PLA or PLA+ filament.

use this link to join CGTrader and download my designs.

https://www.cgtrader.com/designers/PJD1974?referral_id=3218445