The Scissors Crossover

Before track can be laid on the Mother of All Helices (MOAH) I had to build a scissors crossover. Since the helix is designed to be serial storage for trains, the crossover is at the entrance of the helix and will allow me to store trains from either direction on either track of the helix. It will also allow trains into and out of hidden staging which will have a connection on the inner track on the lower level of the helix.

To this end, I had built four Fast Tracks jig-built turnouts (2 right hand and 2 left hand). I intended to build these into the crossover. Unfortunately, I could find no good information on building a scissors crossover. Fast Tracks had printable templates for building one in HO or smaller scales, but they were not available in O scale; and they were for a much tighter track center spacing than I was using so they could not be enlarged to equivalent O scale.

The NMRA had no data on building one using the #6 turnouts that I had on hand. Particularly I wanted to know the degree of the crossing in the middle as a function of the turnout number and the track center spacing.

Paul Mallery's "Trackwork Handbook" had instructions for scratch building a simple crossing and it was of some help.

I guess that I could have calculated the angle of the crossing using geometry had I put my mind to it. Instead, for better or for worse, I decided to wing it and improvise as I went.

So I started to lay out the crossover on the back of my 2x4 ceiling tile where I build most of my scratch built track. The two left-hand turnouts were positioned first as these form the facing-point crossover which will be the most often used route through the crossover. The turnouts had been built with extra-long rails on the diverging routes and I joined these to form a continuous route through the crossover.

Here's what that looked like:





Next, it was time to start fitting the right hand turnouts. The straight legs of the turnouts were temporarily joined with rail while the diverging leg was butted against the left hand crossover. These pictures show it best.





To keep the straight routes in line and in gauge, I used Fast Tracks "Sweep Sticks". I had what I thought was a brilliant idea to cut one of the sweep sticks into a tool that would hold the intersecting rails in gauge as well as to the proper angle while they were being soldered to the previously laid crossover. The next photo shows how I used sweep sticks.



The angle-cut sweep stick did not work out as well as I had planned. I did not have enough hands to hold the rail tight against the sweep stick while wielding the soldering iron and the solder. However it worked well enough to keep the track just within tolerance by the NMRA gauge.

Once the first right hand turnout was soldered in place the problem of how to align the turnout on the opposite side arose. This time I had better luck with improvising a tool. I made a tool out of 3/4" x 1/8" aluminum, notched to fit over the in-place rails and which would hold the off-side turnout rail in alignment with the turnout already soldered in place.





The detail shot shows how the tool is held in place with wooden clothes pins with their handles turned around and end-for-end so that the straight legs are pinching the tool to the rail. It's important that a tool like this be used on the gauge side of the rail and not on the off-side.

The tool, with a lot more clothes pins, was also used to align the rails in the center of the diamond:



Here, the two running rails in the center of the diamond are aligned and soldered in place:



Here's the scissors crossover with all running rails in place:



Now came the really tedious part - the guard rails. The guard rails will have to have part of their base removed to fit against the running rails; and where their ends butt against the running rails they will have to be filed to an angle as well as having the base relieved to fit snug against the running rail.

Before the guard rails could be fitted the flange ways had to be filed through the running rails. I tried, without success, to use a Dremel tool for this purpose. Even though I have a cutter that it the exact size for an O Scale flange way, I could not hold and guide the tool accurately enough to cut a good flange way. In addition the tool had a tendency to catch on the rail and become uncontrollable.

During the fitting of the guard rails and the filing of the flangeways, I ran into a curious problem. After checking the work with the NMRA gauge, I would run a truck through. This particular truck was removed form a car where I had replaced all of the wheel sets with Precision Scale wheel sets. Oftentimes one wheel set on the truck would have no problem going through, but the other would hang, usually catching the back of the wheel set on the guardrail or in the flange way. For the longest time I did not question what are supposed to be high-quality wheel sets, and I did a lot of extra filing to get the thing to pass through.

Finally frustrated with the amount of filing that I was doing, I checked the wheel sets. Sure enough one wheel set on the truck was wide-gauge. So I got the other truck from the original car and start using it - and the problem persisted! This time I checked the wheel sets early and one wheel set on this truck was wide too! So out of four wheel sets, from a reputable company, two were out of gauge. Just goes to show, take nothing for granted.

Here are pictures of the completed scissors crossover.











Placement of the PC ties was ad hoc and did not follow any pattern. Fortunately, this scissors crossover will be hidden from view (but still easily accessible) inside the helix; so the fact that it's not competition quality is not an issue. Still it's a shame that no one will admire my handiwork.

I will have to build another one of these for the top end of the helix, to get re-routed trains back on their proper tracks. But that's a job for April.

It's Itsy-Bitsy

I've finally finished a project that I've been thinking about since 2007, namely, creating a scale B&O Color Position Light (CPL) dwarf signal. What's the big deal, you ask? It's to exact scale and it's itsy-bitsy.

The story starts at the 2007 O Scale National Convention. I attended a clinic by a gentleman who was using 3D Computer Aided Design (CAD) and a jeweler's 3D wax printer to create O Scale parts. He would design a part in the CAD program, send it to the wax printer which would print a copy of the design in wax. The wax model would then be used to make a rubber mold, the mold would make more wax copies which were then used in a conventional lost-wax process to produce the final parts in brass.

While this sounds complicated it was, for its time, an inexpensive and fairly simple way to get to finished parts if you needed more than one copy.

At the time I had been looking into various 3D printing processes concentrating on stereo lithography (SLA), but the costs of those machines were astronomical and having models produced on them was far too expensive, even for one piece; so the wax printer/lost wax process was promising.

Soon after the convention I settled on the B&O dwarf signal as the model that I wanted to produce in O scale. It had never been done to scale; MTH (and, I believe, Right-o-Way) having produced grossly over sized versions for the 3-rail O gauge market. Also, I had the plans for the General Railway Signal Type 'VA' B&O CPL dwarf signal so that would make it easier.

Here's a picture of the prototype.



This dwarf has two additional markers and a sign on top, but the basic signal is the lower eight lights.

The CPL dwarf is a difficult signal to model. Eight lamps, each with visor, on a small target would be difficult and expensive to produce by conventional machining; even to build a single master for reproduction by casting. Many 3D printing processes, like fused deposition modeling (FDM), are too coarse to produce a small, finely detailed model.

In 2009 I took a job where we use 3D printing (out shopped) to check designs before we commit them to production. I had a chance to sample several different 3D printing processes as well as get some exposure to 3D CAD. Now I had access to the tools and some people who could help me out.

Here's what the 3D model of the basic CPL dwarf signal looks like:



This model is somewhat simplified. The nuts and bolts on the case are not reproduced; nor are the ribs on the backside of the case back; nor are the edges of the case rounded. As it turns out, none of these are visible at normal viewing distances.

I still needed to find a supplier that could produce the models without charging $80-100 for each one. Enter Shapeways. I'm not the first modeler to discover Shapeways 3D printing service. Their service is unique; they offer several different 3D printing processes, they offer worldwide shipping, their prices are reasonable and they are modeler-friendly.

I designed the model to use the full capabilities of Shapeway's "Frosted Ultra Detail" (FUD) material which could hold the smallest features out of all of Shapeway's processes. FUD is a 3D printing process called 'PolyJet', which prints a part using a UV-cured plastic shot from a multi-nozzle print head much like your inkjet printer prints. The signal's shell, which is hollow to allow for illumination, is made to the minimum thickness allowed by the process. With some trepidation as to how they would appear, I made the visors a little thicker than the minimum for strength.

Since the model was done on a heavy-duty 3D CAD program (Solid Works) it passed all of Shapeway's tests for printability. After I uploaded the model to Shapeways, I discovered, to my delight, that the model could be produced for well under $10 (US); so I ordered one.

When it arrived, it struck me just how tiny this thing is. It's so small that I am convinced that it could not have been produced to scale, with scale-sized visors, by most other process, especially casting. Here's what the model looks like.



The model is on the dining room table's tablecloth and that's the weave of the fabric that you can see. This gives you some idea of the size of this dwarf. I'm really happy with the way the visors came out. They are 20 thousandths of an inch (less than one inch in O scale) and although that is thicker than the prototype, you cannot tell from looking at it.

Here's a picture on the layout:

That's an O scale E7 in the background. The O scale figure is 1.43" tall (36.43 mm).

I have made some changes to the back cover of the signal, which is a separate piece, and I have another batch on order. When those arrive I'll experiment with painting (Shapeways could not advise me on compatibility of FUD with paints) and illuminating. I'm sure that this signal can be illuminated with 'chip' LEDs; but that will require me to design and lay out a circuit board, which will take a while.