Modeling Scale Test & Repair Cars - (Part 1) SPMW 790 & 438

Over the years I've bee researching the SP, there have been many interesting prototypes that have popped up.  As time moved forward more research materials came to light.  Often this process would allow me to finally build or rebuild models of them.

SPMW 438 "Scale Repair Car" and SPMW 790 "Scale Test" in their post-1958 MW Gray color scheme - Eddie Sims collection

One such project is a "Scale Test & Repair" outfit.  The January 1956 SPMW Roster shows several scale cars, including the SPMW 790.  This didn't mean a lot, other than finding a prototype for my Walthers 4-wheel Scale Test Car, which I built about 20 years ago.  Recently, Eddie Sims shared a photo with me of the SPMW 790 with an unknown car, which had a number that was hard to read.  However this mystery car is stenciled "Scale Repair", and I had a good guess as to the number range, which I looked up in the roster.  Turns out this is the SPMW 438, an ex-B-50-10 class boxcar, converted in 1950 for use as a Scale Repair Car.  I've read about such repairs and servicing, which the track scales need to be checked on a regular basis, and when needed, repaired.

SPMW 790 - Scale Test Car

The Early Years

Stock Walthers 4-wheel Scale Test Car painted black and lettered with some goofy scrap decals in the early 2000s.

The Walthers model is plastic without much weight to it.  Brass models are available, but I didn't get one of those.  Several 1/4 oz lead weights were fitted inside the plastic model and the axle reliefs in the floor were cut larger so the detection chips used for the LMRC signal system (Chubb based) would function.  I also fitted "Scale" KD-58 couplers.  Intermountain 33" wheels were fitted.

Prototype Photos

SPMW 790 with 16-section sleeper - about 1960 - Victor B D'Agostino collection

More photos showed up over the last couple years, including this one from Victor's collection.  While also a later era shot, it shows the SPMW 790 moving with an ex-16 Section sleeper bunk car of some sort in a train.

Operations

Note that the scale test car must be operated near the rear of the train, but it may NEVER be operated as the LAST car in the train.  The scale test cars do not have working train brakes.  The hand brake is only to hold the car when spotted on the scales.  The cars are designed to not change weight at all, thus allowing for accurate measurement and calibration of the track scales.  Some more modern scale test cars, like the 'master' calibrated cars are not allowed to be moved on their own wheels between the master scales across the country.

Upgrades

The Walthers model I felt was lacking in 2019 when I was shown Eddie Sims' collection photo of the 790, which clearly shows the lettering it received after the 1958 change to overall light gray.  Change the body back to black and the lettering to white, and I'll be able to model it before the change to light gray.  The decals I'll be using are from Microscale 87-1013 and left over fragments from OwlMtModels 1210 SP F-50-series white decals, from when I've built several of these models.  Mostly I'll be using the OMM reporting marks and number decals.  I'm also planning to make up the "SCALE TEST" from the single letters from the relief outfits and other words in the right size.

Grab Irons

The first step is removing the decals and then the grab irons.

I removed the old details with some MicroSol on a brush and some light scrubbing with a toothpick to rub the white decal ink away.

Grab Irons removed and sanded/filed clean.

I started upgrading the details of the scale test car by cutting off the cast-on grabirons and replacing them with 0.012" wire.  New grab iron holes were center marked with my carbide scribe and then drilled at 0.015".

The plastic hand rails removed.

I also noticed that the stanchion hand rail was damaged and so I'll be replacing that with metal wire pairs fashioned by hand and cut to the right height.  The two mid-rail stanchions will be soldered to the continuous section.

The new grab irons partially installed, the end grabs will be next.

I'll be painting the grabs white, along with the vertical sections of the hand rail.  I'll probably also install the air hoses for the through air pipe on the car, as it has no air brakes.

The cleanup for taking down the cast-on grabs has really done a number on the paint job.  The next step will be the repainting of the model black.

SPMW 438 - Scale Repair Car

The photo I'll be using to model SPMW 438.

The starting point for the SPMW 438 is an Accurail 40ft single sheath 8-panel boxcar with wood doors and wood ends, basically a great starting point for SP's B-50-8/10/11 class boxcars!  Originally the SPMW Roster shows the 438 as a B-50-10 class car, but the original car number is 25831 converted to MW service 8-7-1950 and assigned as 'Scale Test (Repair)'.

Basic Construction

The basic construction of the car follows the normal process for an Accurail boxcar.  Sheet lead is cut for the floor weight and to fit between the centersills in the underframe. Screws 2-56 are used for attaching the coupler box lids and trucks.

Underframe Changes

The prototype car appears to be riding on leaf-spring equipped Vulcan trucks, so I'll probably be using the KD HGC Vulcan truck with scratch built leaf-springs.

The bolsters will need to be modified to include the roping staples, which are visible above the trucks.

Body Changes

The obvious changes to the body start with the removal of the door and cutting four windows.  A smaller change, but I feel worth while doing, is adding the extra diagonal straps, which many B-50-8/10/11 class cars have at the corners.

Marked body with mechanical pencil, laying out the changes.

I started several months ago by laying out the changes with a mechanical pencil.  I roughed out the locations for the new diagonal braces and windows.

Carving off the diagonal braces where the windows will go.

I started by carving off the diagonal braces from the panels where the windows will be cut later.  A No.17 Chisel Blade was used to carefully whittle down the ribs.  I tried to avoid carving into the wood board detail. 

The fourth panel diagonal is now removed.

Once I got it down to nearly the same level, more fine work with the chisel blade, carbide scribe, and No.11 X-Acto blade.  The wood grain is basically restored in the photos above and below.  The gusset plate at the top and the lower edge are retained, as on the prototype.

Starting to mill down the center of the door area.  Lead strip in the centersill is visible.

I started by milling out the inner parts of the door in several steps with 1/16" and 1/8" 4-flute flat endmills, held in my drill press.  I need to get my full XY table going, but for this process a good drill press with Z-stop and judicious use of clamped "fences" to keep the model aligned worked.

Can't See Black - Primer!

At this point I shot some Tamiya Sand as a primer so I could see my pencil on the carside.

At this point I continue milling down into the carside to the depth of the wooden sideboards.

Left side door milled down and 'man door' cut into the door area.

In a couple of places the endmill bit and lifted the carside, digging a bit deep into the door area, but did not punch through the carside.  The deeper gouge of the 1/8" endmill above the door will be filled in later with Squadron Putty and primed over.  I would have preferred not to have the gouges happen, but at least they're easy to fix.

Window holes cut in the right side of the car, notice this is the reverse side from previous photo.

I remarked the window locations and drilled through with two 1/8" plunges of the endmill.  I opened the rest of the window opening with my key-hole razor saw.  Then I finished the openings for both the door and windows with No.11 blade and files.

Diagonal Bracing & Man-door Framed

Progressing with the Man-door and diagonal corner braces.

I started framing the door way with 2x4 scale styrene strip with Tamiya liquid plastic glue.  The man-door is made from a piece of 0.020" styrene with 0.040" V-Grove sheet.  The doors are cut 4ft wide and 6.5ft high.  I also made a backing piece pf sheet of 0.020" styrene which mounts to the back side of the carside.  The door V-grove piece is then mounted to the backing piece.

Diagonal 2x4 braces added.  I scrapped the primer off of the carside so the glue will bond well.  After installing the braces, I filed/sanded down the thickness of the braces to appear stacked at the top gusset joint.  The right side diagonal braces were fun to cut and fit around the cast-on ladder.

The last step on the carside in this series will be to frame out the windows with plastic strips, which I'll cover in Part 2.

End Modifications

Stock end with outer vertical brace from the right side of the end.

SPMW 438 prototype photo cropped - Eddie Sims collection

The end modifications include removing the right side vertical brace column.  The SP cars in these classes had diagonal braces instead.

End with diagonal 2x4 braces installed and 3x6 door header added to end.

I also cut down the grab irons and center marked the replacement metal grabs with my carbide scribe. I'm going to leave the ladders alone, as the Accurail ladders are very fine, and I can hide the cast-on look with painting and weathering.

B-end of the SPMW 438 with diagonal brace cut around brake platform.

In Closing

I plan to install A-line stirrup steps will be installed as I get closer to completing the model.  New wire grab irons will also be installed in the non-ladder corners.  The man-doors will receive a center lap-joint board and some other small framing details.

SPMW 790 and SPMW 438 status wrapping up work on July 18, 2021.

I'm going to wrap up this blog post here as it is getting rather long.  I'm looking forward to painting both models and decalling them, but a number of the next steps will come before I can do the final painting.

Jason Hill

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