Saturday, April 11, 2020

Dufferin-Montmorency Highway Overpass - Mark II

Ten years ago, I built the first version of Dufferin-Montmorency Highway overpass. At that time, the club layout was focussing on Limoilou yard and it was used to create both a sense of place and hide the hole in the wall.

It was also my first modelling blog ever written here, so you can say this structure was part of Hedley-Junction DNA. For the new diorama/switching layout, I also need a model of the exact same structure. However, this time I decided to learn from my mistake and make a better job out of it.

Back then, I basically never used any kind of putty, never really thought about sealing wood and MDF components before painting even if I knew it would help a lot. I wasn't very keen on sanding too before applying primer and between coats of paint. But that structure did look cool and was a favourite of many people how visited the layout. Often, we considered reusing it, if only it could have fit the scene and space available.
Original overpass: blobs of glue and damaged material.

Before build the new overpass, I had to determine where to put it, how it would relate to the tracks and where pillars would be. Easy to say, but as you will find out later, I made a little mistake and had  to take strong measures to correct it.

Original overpass: paint had a different texture depending of material.

First step was to assess the structure. Back in 2010, I made several compromises in terms of height and pillar spacing. I also made the parapets far too high while making a few errors how the crossbeam supported the stringers (concrete beams). I thought I should follow the prototype closer, but in the end, I reused the same dimensions as my first scratchbuild. The reason was simple, the prototype span is larger than my layout width! Also, having only one span would look silly and wouldn't hide the fact there is nothing on the other side. Having a forest of pillars really helps to create the illusion of a real visual barrier. In that respect, artistic considerations has the upper hand.

The pillars create a new and interesting vantage point to railfan the trains.
Another decision was to have the overpass complete on both side. On the first version, it was facing a wall and I didn't bother. However, this time, the overpass is floating in the middle of nowhere and needs to look good on both side. Also, even if there is a wall, I still would do both side, because I thing it looks better when you see all the lanes. Cutting a lane in the middle wouldn't be visually interesting and creates that "cropped" image appearance I'm not too fond of. Think of it in the same way as flat structure against a backdrop. You reach a threshold when it no longer looks believable and the same apply with overpass hiding the end of a layout. Too many great layouts are visually ruined by these compromises that should have simply be avoided.

Original overpass: the drain pipes made of sprues are a detail to replicate

While workmanship on the original overpass wasn't top notch, it was still a well-thought piece of modelling, so I decided to keep the recipe and only improve it where I could. The original overpass was made out of styrene and MDF. The decking and beams are concrete and thus MDF was my first choice material. Pillars have neat flutings on their corners, thus they would be easier to scratchbuild out of styrene. The parapets have very intricate 1970s random grooved pattern which was extremely fashionable back in the days in civil engineering circles. They can only be convincingly modelled with styrene. As for the crash barrier in the middle, MDF was my first choice too.

As many knows, MDF and styrene glue together extremely well with thin CA glue. The bond is permanent and almost impossible to break. The MDF will delaminate before you can break the glue bond. Also, the bond is instantaneous. You don't have even half a second to wiggle the part in the right spot. It must be perfectly dry aligned, then glued in place. It may be, as you can guess, both a blessing and a curse. Learn to work with it, and it will open a lot of possibilities. Interestingly enough, CA glue on MDF can be easily sanded down to a glass-like finish. This is of extremely great importance because when painting materials with different porosity, you get variation in shines that look horrible and only get worst with weathering.

All surfaces sealed with CA. When primed, the wood grain disappear.

So here's another tip for working with MDF. Seal your component with thin CA glue. Apply it over all the faces and when dry, with fine sandpaper, polish the surface. Not only it will reducing warping in the long run, but the surface is perfect for painting. And it works also on regular wood. Since I didn't have enough MDF for the concrete beams, I used leftovers from a 3/4" thick pine plank. The CA glue helped me to completely hide the wood grain.

The central crash barrier was quite a challenge. The particular profile on such concrete barrier is hard to replicate. Back in 2010, Louis-Marie did it on a table saw, but as he explained me, it was the perfect recipe to lose a few fingers in the process. It was time to find a safer way to do it. The new process is simpler, I used a 1/4" plank of MDF that was about 3 inches high to have enough material to grasp in a safe way. On each side of the plank, I cut notches about 1/4" deep and 1/16" wide. Once the profile was right, I then cut it from the plank at the correct height, leaving an inverted T-shaped base. The barrier was then liberally covered in CA glue and when dry, I used a file to flare the base and top of the wall. I repeated the process several times, sanding down material until satisfaction. Interestingly enough, CA pooled into the "T" crevice which smoothed the profile, making a visually compelling slope. On my prototype, the crash barrier plinth is covered in galvanized sheet metal and I really wanted that detail to be carried on the model.

As for the order of assembly, I started by gluing the concrete beams (stringers) first on the deck. When dry, I cut the deck and beams on the table saw to length, making sure to induce an angle for visual interest. Then, the crossbeams made of 1/4" MDF were added. They do wrap at each ends around the beams, creating a "C" profile or a kind of clamp. All surfaces were sealed and sanded twice at this point.

It was then time to make the pillars. They are basically styrene boxes. To create the notches on the corners, I simply glued another sheet of styrene. All angles were sanded and round to look like cast concrete. Then, using a square and sandpaper, I made sure each pillar was perfectly perpendicular. As I said, CA glue, MDF and styrene aren't forgiving. you must dry test your parts before gluing. When everything was exactly as wished, pillars were located on the crossbeam in their exact position and thin CA glue was applied. It soaked right into the MDF, creating a very strong bond. Full disclosure: I did glue two pillars in the wrong place... I thought I would break the model when I had to take them apart. Not an experiment to replicate.

Oups! The pillars are too close to the track!

The last step was to build the parapets. They were crafted on the workbench and made longer than the overpass. I prefer to cut them to length once glued on it. They are made of several layers of styrene sheet and stripes to match the random prototype pattern. Later, a styrene railing with grace them.

A man can barely walk by the train without getting hit by the locomotive.

With the overpass almost completed and ready for paint, it was time to test it on the layout... and the biggest of my mistakes became instantly apparent. Maybe by sheer naïveté, I thought having the track quite close to the pillars wouldn't be too bad. Unfortunately, it looked both unrealistic and visually unbalanced. Basically, about 4 days of works for nothing.

Serious alignement issue
However, while looking at the track, it was evident they weren't straight. It was a little bit weird since I was certain the alignment with the pillars was correct when I planned the layout. Using a long straight edge, I found out the misalignment was severe, at least 3/8" which in HO scale is almost 3 feet. In another place, I wouldn't have minded such an insignificant detail, but given the trains were almost scratching the pillars, I had to to something.

Gaining 3/8" makes a great difference

Thanks to Lance Mindheim, I glued the track with white glue. After wetting the track again with water, it became soft again and I was able to move the track to the correct alignment. It certainly wasn't a walk in the park, but it did work. After soldering back the feeders, I tested the overpass again. Now it looked right! Yes, I lost half a day correcting my mistake, but I know it would have been detrimental to keep it as it was. In the process, I had to scrap the complex road I had painstakingly built to fit the track geometry... so no, it wasn't an easy decision to make.

Final location with road

Nobody is immune from mistakes and addressing them when they appear is what makes you a good modeller. In fact, a good deal of being a better modeller implies simply to learn to not compromises with shoddy results and try to fix them. It's the only way to improve as rebuilding from scratch this overpass proved us.

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