Tunnel portals

I'm sure the observant among you would've noticed there's a few tunnel portals on my layout. There's a lack of proper NZR tunnel portals available to modelers, so I decided to create my own using the modern day miracle magic of 3D printing.

First step was to find out what information's available. As it turns out, the NZMRG Journal December 1992 edition has a "plan page" on NZR tunnel profiles, to various plans. It appears there wasn't really a standard design for tunnel portals, just a series of plans for each tunnel. I photocopied the plan page and stuck it to some card, cutting out the outline of the profile for Plan 10-229, which seems to have been from a tunnel on the Midland line:

Boring.

(If you look closely you can see I made some basic measurements in mm before photocopying the plan)

Cut-out ready for a test on the layout.

Then it was off to the layout to test the dimensions:

Lurkin' ZA. Note the portal will be where it says "tunnel", in case that isn't clear...

That all seemed to fit (although I realised the bottom of the portal needs to be slightly elevated otherwise larger wagons / locos will scrape it, mind you that is realistic...). As you can see the first attempt at making a 3D model (above) didn't come out so well, it seems a lot of the blocks weren't properly enclosed. So I re-cut the design and this is what I came up with:

The edges of the portal are "cove", it'll be interesting to see how this comes out in the printing process.

Coincidentally this portal is now on my Shapeways store.