Friday, December 30, 2022


One of the signature structures on the historic SP Cascade Line was the engine shed at Oakridge.  Oakridge served as the helper station at the base of the long mountain grade in the steam era.  Four tracks including one stub track served the engine facility.  Initially, servicing was done out in the open.  Sometime around 1938, an engine shed was erected. This may have coincided with installation of locomotive inspection pits.  Working out from the main line and yard tracks, the first track was not covered and served as the engine facility run-through track.  The next track held the “long pit” and was covered by a very long shed—enough to cover two cab-forward steam locomotives.  The third track held the “short pit” and covered a single cab-forward.  The stub track was the fourth track and had a wall on the stub end.  The shed was built using retired rail for framing and corrugated iron sheathing.  Partial side sheathing was mounted just under the roof.  


Oakridge engine shed mock-up, seen from the mainline and yard side.  The “long pit” shed section is in the foreground.


The pictures I have of the shed are covered by intellectual property rights, so I am not free to publish them here.  I can point to one photo on Joel Ashcroft’s Southern Pacific in the Cascades website:  The shed shows in the left half of this photo as well as in the lead photo for the Oakridge photo pages.


Once I committed to modelling the historic SP Cascade Line, I knew I would need to scratch-build a model of this structure.  I decided to start with a mock-up while I resolve several construction issues for a more accurate model.  I elected to make the “mock-up” a fairly detailed model on its own, finishing with one of my current favorite materials—image textures from Clever Models.  Some modelers argue that making mock-ups, particularly better-detailed ones such as mine for this project, is a waste of time.  The mock-up is intended for replacement.  For my Oakridge engine shed, I needed to get a better idea of how the engine shed would look and to resolve a number of construction and size issues.  My mock-up was time well spent.  While some of the construction challenges I faced were unique to the mock-up, they exposed analogous issues that must be addressed in a complete model.


I began by roughing out dimensions for the shed.  I do not have accurate plans for the shed and needed to estimate everything based on a modest set of photos.  I very quickly discovered that although my track spacing for the engine facility seemed generous when fully exposed (not covered), I likely will need to increase the track spacing from 15 scale-feet to more like 20 scale-feet.  This is based on both the appearance of the completed mock-up in position and from careful study of a couple of the photos showing the geo-East end of the shed with the stub-track wall.  


With rough dimensions, I began construction of the roof.  I used triangular end pieces and an identical middle piece to help form the roof pitch.  These formers were separated by balsa strip out towards the long edges and a central foam-core spine.  More foam-core was used to form most of the remaining roof between the spine and the roof edges.  These were incomplete panels as the foam core has real thickness.


Roof section formers composed of chipboard end and center roof pitch formers, foam core center spines and balsa strip edge formers.


I then turned to making post assemblies using Evergreen styrene strip.  I used 0.060 x 0.080-inch strip for the posts and 0.040 x 0.12-inch top and bottom plates.  I started out placing the posts at 20 scale-feet intervals, but a check of photos sent me back to add more posts for 10 scale-feet intervals.  This was one of many brain “interruptions” during this model effort.  I also added longitudinal strips to hold the roof-edge side wall sheathing and a couple of other long beams seen in photos.  I think the “beams’ may actually be steam lines on two of the post assemblies.


Post assembly construction, here with 20 scale-feet post spacing.


One feature seen in photos are knee braces just under the roof trusses, presumably keeping the posts square to whatever roof truss structure was used.  I used my NWSL Chopper with a jig piece set to help make 45-degree end cuts on same-length knee braces.


Cutting knee braces with an NWSL Chopper.  The cutting jig width on the other side of the chop blade was cut to 3 scale-feet wide.


I attached the styrene post assemblies to the wood roof spans using canopy cement and a bit of gap-filling CA adhesive to set several of the posts in position quickly and at the desired square joint.


Attaching the outer post assemblies to the roof sub-assembly.


At this stage, I was glad this was a “mock-up” as my placement of several of the cross-roof-spans was imperfect.  A final model will need to have real roof trusses that join precisely to the posts.  What I have is good enough for the mock-up and certainly conveys the open framing seen in photos.


When I sheathed the roof assembly with sections of “corrugated” image printed onto cardstock, I chose to augment the glue-stick adhesive on the cardstock with a brushed-on coat of thinned white glue on the subroof.  This was a BIG mistake!  The various bits of cardstock in the assembly—likely the foam-core sheathing—tightened up as the glue set. The result was a “pagoda” roof that bowed up on the ends.


Initial roof sheathing.  Close inspection will reveal the end posts have lifted up relative to posts more in the center of the structure creating a “pagoda roof” effect or a rocking structure.


I tried to correct the bowing by inverting the structure and applying another thinned white glue wash to the underside of the roof.  This did not cure the problem and created a second problem of printed image bleed at the roof peaks (lowest points on the inverted structure….).  I finally settled upon slicing each roof panel section (every ten scale feet) with a razor saw and then inserting cardstock into the gaps.  This seemed to straighten out the structure, but some bowing remains end-to-end.


Correcting the roof bowing.  The green splotches along the ridgelines are from the first correction attempt using diluted white glue on the roof assembly underside.  Cardstock spacers inserted into razor saw cross cuts were my second straightening attempt.  With the shed assembly seemingly straight, I applied new roof sheathing.


I assembled a wall for the stub track stall by laminating corrugated image cardstock back-to-back.  I cut into this for the window seen in photos and then applied an impression of framing on the inside wall.  


I learned a lot as I built this structure.  Adjustments to the track layout are called for.  I need to sort out how to properly frame the roof.  At least 51 roof trusses are implied by the number of roof posts seen in pictures.  I need to figure out what spans between roof trusses.  I also need to locate a suitable corrugated sheathing material—something that attaches well to the structure framing.  


For now, I have a mock-up that conveys the major features of the structure.  It may need to last for quite a while…


Oakridge engine shed detailed mock-up.