BACKDROP SPINE INSTALLED

My plan for the HO scale SP Cascade Line features a “C”-shaped peninsula that forms the “Valley Core.” (http://www.blogger.com/blogger.g?blogID=1100386727262758268#editor/target=post;postID=8623016313855752576)

The Oakridge and Eugene Depot scenes are separated by a backdrop which continues to wind through the middle of the peninsula as it curves around to Springfield.  This backdrop spine needed to be installed before track laying.  Indeed, I spent a fair bit of time up on the subroadbed “table” installing the back drop frame work, sheathing that frame with hardboard panels, spackling the joints and applying a first coat of paint.  Far better to do all that work now before track gets underfoot.

The backdrop spine was formed from strips of plywood cut to 2 ¼” wide.  Much of the spine is straight, but it does include the broad curve separating the Willamette River crossing from RR-East Oakridge and Westfir.  I also placed an “S”-curve in the section between the Eugene Depot and Oakridge Depot scenes.  Top and bottom pieces for the frame were cut from two slabs of plywood, joined temporarily by screws.  As seen in the photos, the frame is a simple box frame of top and bottom pieces joined by straight vertical pieces.  The backdrop is 3 feet high on top of the 48” benchwork and roadbed base level.

Backdrop frame behind Eugene Depot.

Even at the framing stage, the introduction of the curve sections, including the “S”-curve provided a fairly rigid structure.

Another feature of the backdrop frame is the installation of conduit to provide electrical runs to the top of the backdrop.  These will be used for signal repeaters.  A couple of conduits at the basement’s central post will be used for the NCE throttle radio antenna and for a fast clock to be mounted on the post.  The conduits are made of sections of “smurf” tube (named for the blue color) that I had left over from a cable run installed in the basement ceiling as the house was built.  The conduit width (installation hole is 1 1/8”) set the overall width of the backdrop spine at 2 ¼”, leaving adequate material on either side of the installation holes.

Backdrop termination at end of Springfield peninsula.

The backdrop spine running down the Springfield peninsula needed to be terminated.  At the suggestion of Seth N., after a visit , I elected to flare out the backdrop to a relatively broad cylinder as a terminator.  I used a concrete pier form, which is 8 inches wide.  One cannot see both sides of the backdrop simultaneously.  Indeed, one cannot look directly down the plane of the backdrop.

The backdrop is sheathed using 1/8” tempered hardboard.  I chose this “old school” technique because I was well familiar with it and willing to do the joint filling work.  The backdrop is quite long, so joints would have been necessary for most any material.  The Springfield peninsula backdrop terminator is sheathed with a scrap of vinyl flooring, using the smooth underside of the flooring on the outside. 

Backdrop spine with hardboard sheathing.  The backdrop “S”-curve between the Eugene Depot and Oakridge scenes is shown.  Also shown is a flare on the Oakridge side that meets the edge of the main house support post.

I started by attaching the hardboard panels to the top of the spine with wood screws.  The bottom and some of the edges were attached using 5/8” brads with a staple-brad gun.  I eventually tired of being super-careful with the screws and attached most panels with the brads.  These mechanical attachments were needed only long enough to allow the construction adhesive applied to the framework to set.  The problem with the screws is that 1/8” hardboard does not leave much margin for the screw countersink while still leaving enough material to hold it all together. 

After at least two coats of vinyl spackle and sanding, the backdrop was ready for paint.  I primed the backdrop using the same light blue applied to the basement walls.  The color used is actually about halfway between the sky color well above the horizon and the almost white haze layer seen closer to the horizon.  As such, it is a good primer.  The fade between “upper” sky blue and horizon haze will be a project in the near future.

Backdrop with first coat of primer.  A modest-length train has been placed into the Eugene Depot area to help with visual scaling.