TUNNEL PREPARATION – 3 -- MORE PARTS

Preparing for the scenic effect of tunnels on my SP Cascade Line involves many steps.  The previous pair of posts described major pieces needed for each tunnel—tunnel portals and the initial tunnel liners.  https://espeecascades.blogspot.com/2017/11/tunnel-preparation.html

https://espeecascades.blogspot.com/2017/11/tunnel-preparation-2-casting-portals.html

As I went into production casting tunnel liners (forty halves needed!), I continued creating additional casting masters needed for the tunnel entrances.  Specifically, I needed wing walls—triangular retaining walls alongside the portals—and another portal for the rock shed galleries that lead into a number of the tunnels on the Cascade Line. 

Tunnel wing wall masters.  The rear (left) wall needs to have the form board strips trimmed.

Wing wall mold box.  I intended mounting the two wing walls in a more compact mold box with the two triangles nearly forming a square.  Convention overcame me when I placed the walls on the mold base plate.  I mounted them as mirror images.  That led to the diagonal mold box walls at the top.

I used the same technique for representing form boards on the wing walls as I used on the two main portals previously described.  Various thin thicknesses of Evergreen styrene strip overlaid scribed sheeting which provided a horizontal line reference.  As with the wide wall portal, the wing walls can be cut down to whatever size or angle is needed for a specific installation.

The Cascade Line had a number of open gallery rock and snow sheds leading to the tunnel portals at higher elevations.  See Tunnel Nine’s East Portal: http://spcascades.railfan.net/TUNNEL9.html

And the photo below:

Rock and snow shed at RR-West portal of Tunnel 5.  A. de Gues photo.

The sheds were cast in concrete.  I will build my gallery sheds using styrene tubing for the pillars and hardboard sheet for the roofs and back walls.  The tall and relatively thin pillars do not lend themselves to easy plaster casting.  The gallery shed portals need to be a common design with the “1926” date casting.  I built a portal master using the same 5/16 inch tubing that I will use for the pillars.  I will hope for the best when pulling these out of their molds, though a break can be repaired with glue. 

Rock and snow shed portal master.

I just got a new bag of US Gypsum Ultracal 30, so I can cast these parts plus the regular tunnel portals and tunnel liner halves in quantity.

TUNNEL PREPARATION – 2 – CASTING PORTALS AND LINERS

Adding tunnels to my railroad involves considerable preparation prior to closing the area in with terrain.  The previous post described building masters for tunnel portals and half of a concrete liner.  It also described making the silicone molds using the masters.  The post can be viewed at:

https://espeecascades.blogspot.com/2017/11/tunnel-preparation.html

The tunnel project has now moved into a production casting phase.  I am casting the portals and tunnel liners in hydrocal, a US Gypsum product.  It has been a couple of decades since I last did any casting work for a model railroad.  I needed to relearn a couple of lessons in casting such as how fast hydrocal sets up and how to get it into the mold detail.  My first casting attempt used too much mold release.  It pooled in the mold, obscuring the detail.

First casting of two portals and a half tunnel liner.  Note the yellowish fluid on top of the half tunnel liner casting on the right (tall mold).  This is some of the excess cooking spray used as a mold release.  The resulting castings had very little of the form plank detail of the masters and molds.

Subsequent casting attempts have been far more successful.  I still suffer a little bit of trapped air bubbles, now mostly due to how fast the hydrocal is setting up.  Fortunately, the small bubble impressions are very minor flaws and easily corrected with some spackle. 

Tunnel portal castings.  The form plank detail built into the masters shows with this lighting.  The “1926” tunnel date centered above the portals came through, as well.

As I go into production on these tunnel parts, I am reminded that it takes a while for hydrocal to cure.  There is a lot of water contained in the castings.  I will wait for the castings to cure more before painting.  Meanwhile, I will do some shaping and finishing.  As seen in the portal photo above, I have a bit of mold overflow (like “flash” in a two-part mold) to trim off the back of the portals.

Half tunnel liner mold. The scribed siding lines and a bit of form plank detail is visible.  This mold has been sprayed lightly with mold release.

Cast tunnel liners.  The pair on the left has been positioned the way they will be used.  I need to trim the mating surface on the tunnel top centerline.  The liner half on the right shows the modest detail I built into the master.  Tunnel liner detail quickly gets lost in the gloom inside the tunnel.  Still, the liners will mate well with the more detailed portal castings.

I am now in production on these important tunnel parts.  With ten full tunnels, each requiring a portal and a concrete liner at each end, I have a lot of casting to do.  Consider this a “price” of mountain railroading.