Wednesday, December 18, 2019


The last major terrain gap on my railroad has been the missing mountainside behind Cascade Summit.  The prototype Cascade Summit is located just RR-West of the summit tunnel (Tunnel 3) and is located along the shores of Odell Lake.  The mountain pierced by the summit tunnel continues as a ridge flowing down to the lake.  This ridge provides the background for the Cascade Summit station site.  

My Cascade Summit tracks were built on a benchwork table that extends out from the wall above the lower mainline which has begun the climb out of Oakridge.  This is a "half-mushroom" design feature.  The Cascade Summit benchwork extends five feet from the back wall to the operator aisle.  Cascade Summit tracks are located along the aisle edge, so no great reach is required.  One important use of the benchwork depth was to provide space for the summit wye, used in the steam era for turning helper locomotives.  The summit wye tail tack was located inside a single-ended tunnel.  

I thought I would begin my terrain project in this area by completing the tunnel liner for the wye tail and then encasing this area in terrain.  The deep scene and low ceiling height above the roadbed (two feet) means the terrain will reach the ceiling before reaching the back wall for this area.  My first thought was to build a back wall for the terrain using my standard terrain underlayment of insulating foam.  As I wrestled with this, I eventually realized I would do better with a very firm backing for the eventual top of the terrain--a backdrop.  This began a major construction project made more difficult by tight clearances.  

I began the terrain effort by completing the summit wye tunnel.  I previously reported on my modeling of the tunnel portal and initial tunnel liner in a post this past year:  
Several tasks remained.  First, I needed to paint and ballast the track, as access would be restricted or eliminated by the new efforts.  I then built a solid end of the tunnel.  I used three pieces of 1x4 to form a "U" roughly five inches long. Then I built a foam-core tunnel liner to span the space between the tunnel end and the portal and initial liner.  This foam core liner remains removable. 

Summit wye tunnel liner in place.  The track has been painted prior to ballasting.

I then turned my attention to the backdrop structure.  My Cascade Summit forms part of a large S-curve.  The backdrop needed to follow this same pattern.  This meant corner coves at the ends to meet the existing walls and another cove in the middle--right over the wye tunnel.  I began by building support structures for these curved backdrop segments.  I cut top and bottom profiles from plywood, temporarily screwed together to get a common curve.  Once separated, I joined the top and bottom plates with sections of 2x2.  The end corner pieces were full height for this area--about two feet tall, though I chose to leave a small margin between the ceiling and the backdrop structure.  The backdrop cove over the wye tunnel needed to provide clearance for that tunnel for subsequent maintenance.  This resulted in a modest height cove former, mounted on legs attached to the underlying benchwork joists.

Backdrop cove former mounted above the summit wye tunnel.

With formers for the ends and middle curve mounted, I filled in the rest of the backdrop structure, beginning with 2x2 posts for vertical support.  In retrospect, I should have built the straight sections off the layout as short "stud walls" which would have needed just a few screws to the existing benchwork joists to secure in place.  Ah, hindsight...  I braced the straight sections with knee braces which extend back to the actual wall.  The resulting structure is quite rigid.

Backdrop structure.

Finally, I applied hardboard "skin" to the structure, beginning with the coved portions.  I used most of my supply of hardboard scraps for this effort.  The cove over the tunnel and the straight sections are not full height.  Only the top needs to be continuous as my intent is to build terrain to very nearly the top of this backdrop structure.  I provided support for the bottom of this elevated backdrop edge by toe-attachments of 1x2 horizontal supports using a pocket-screw jig.

Skinning the backdrop.  One more segment is needed to fill the gap to the center (over tunnel) cove.

The curve that began it all--backdrop mounted above the summit wye tunnel.

After the construction adhesive sets, I will begin the process of filling and spackling the backdrop panel joints, filling the screw heads used to attach the panels as I go.  I chose to mount all of the current backdrop panels using construction adhesive and screws.  Earlier backdrop efforts used brads rather than screws for support as the adhesive set.  The limited working space this time and the nature of the support system drove me to use screws for this function.  

I plan to paint this new backdrop with my basic "sky blue," but may not do much of the fading to horizon haze used at lower elevations on my layout.  Stay tuned.

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