EMD F7 in SCALE
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BODY CONSTRUCTION: An Illuminating Task Part I
A locomotive has to have a headlight, and my F-unit is no different. For me, a headlight is not a cosmetic feature. My night vision isn’t good, so I needed a headlight that can actually light up the track to where I could see obstacles laying on the rails, misaligned turnouts, threatening rabbits, etc. Although I’m not a rivet-counter, I’m not willing to accept gross deviations from the prototype.
LED lighting is very bright and efficient, which is likely why many large-scale locomotives use it in their headlights. However, the high color temperature of LED lighting looks nothing like the 74-volt, incandescent lamps used in the real F7’s headlight. Not wanting the LED appearance, I needed to cobble together an incandescent headlight, one that I could run on slight reduced voltage to give it that old-time look, as well as to extend the life of the lamp.
The accidental solution to the problem came about one day as I was using my green “suspect beater” (a large Mag flashlight of the type the police sometimes use) and happened to notice the outside diameter of the business end looked to be about the size of the locomotive’s upper headlight pod. A quick check confirmed my suspicions: the flashlight’s bezel was a near-precision fit into the pod. Discovering that led me to making some sketches of how I would adapt the flashlight to headlight duty. I wasn’t going to use my “suspect beater” as a headlight, so I needed to find another one, preferably black.
The plan was to disassemble the flashlight to the point where I could cut down its body to fit into the available space—most of the body length, of course, is there to house the batteries, which wouldn’t be needed. A pigtail with a two-pin plug would make the electrical connections and I would somehow bypass the flashlight’s switch, since it too wouldn’t be needed. A saddle epoxied to the F-unit’s nose would hold the modified flashlight in position, with the saddle designed so the flashlight could be readily removed if necessary.
A little scrounging around found me a black Mag unit that uses four D-cells—it was on sale for nine dollars, hanging right next to the Mag LED flashlights selling for 35 dollars.
I will come back to why I chose the four-cell unit. I bought two of them.
The next step was to disassemble the unit so I could rework it. Naturally, removing the batteries and the bezel-and-lens assembly, of which the reflector is a part, was easy. Getting the switch and socket out of it was less easy—it wasn’t readily apparent just how Mag assembled the mess. So I fired up an Internet search engine (not Google!) and did a little digging.
While digging, I learned a subculture exists that modifies Mag flashlights to accept five watt laser diodes, for what purpose I don’t want to know (the output from such a laser can be very dangerous). In order to do that, the flashlight has to be fully disassembled so a heat sink can be installed to support the diode. In the process of reading, I also learned the switch and socket are a single assembly and that Mag, believe or not, actually sells replacement parts. Yep! You can rebuild a C- or D-cell Maglite...although I question the economics of doing so.
Anyhow, it turns out the rubber cap on the on/off push button is removable—you can pry it off with a jeweler’s blade screwdriver, exposing the push button’s switch plunger. You access a setscrew through a hole that is concentric to the switch plunger. Recently-made Maglites have a setscrew that requires use of a T8 Torx® driver, which I was able to get at the local Ace Hardware store. However, the shank of the driver was a tiny bit larger than the diameter of the switch plunger’s access hole. My battery-powered drill motor and a #40 drill took care of that problem—I was going to scrap the switch anyway.
Below is a photo of the Torx driver being used on the flashlight.
With the setscrew backed out a turn or so, the switch and socket assembly slipped right out of the body. Here’s what the flashlight looked like after being eviscerated.
Before going any farther, I should mention that that same website that instructed me on how to field-strip a Maglite also had a link to another website that sells parts for doing the laser diode conversion. One of those parts is a lens made from borosilicate glass (same type of glass used to make Pyrex® cookware), which is able to tolerate the intense output of the laser—the stock polycarbonate lens will badly discolor and warp. Also, the borosilicate lens has scratch-resistance, which was of interest to me. So I bought some borosilicate lenses, one for my soon-to-be headlight and one for my green “suspect beater” (the “suspect beater” seemed to be a little brighter after I changed out the lens—go figure).
The next step was to shorten the body, which is an extruded, aluminum tube. I only needed enough body length to support the socket assembly and give me a place to anchor the assembly to the the F-unit’s nose, so the cut was made about 3/4" south of the body’s push button hole. Here’s a photo of the body after the dicing and slicing, with the bezel assembly next to it—aside from lens replacement, the bezel assembly is unmodified.
The next step was to butcher up the switch-and-socket assembly to eliminate the switch. Here’s a photo of the assembly following disassembly.
The switch plunger and its contacts were no longer needed, so they got tossed. I then made up a pigtail and soldered the wires in place, the positive lead to a cap that presses against the center contact on the lamp, and the negative to that longish metal piece with the nut, which is also what anchors the socket assembly into the body.
With the now-headlight wired up and assembled, it looked like this.
The next step was to mount the headlight into the F-unit. The goal was to have the center of the beam focused on the track approximately 30 feet in front of the locomotive. In order to work out the mounting angle that would be required, I did a layout in CAD. It worked out that the headlight needed to be inclined 1.5 degrees from level to achieve the desired focus. Due to the rearward slope of the F-unit’s "bulldog" nose, the included angle between the headlight and nose worked out to 102 degrees. As I intentionally made one of the mounting saddle pieces oversized, it was a matter of doing some grinding to get the right mounting angle, as well as get the saddle to properly fit the internal contour of the nose.
With grinding and fitting completed, I trial-fitted the headlight to the body and energized it to verify its aim. Having done that, I inverted the body, thoroughly cleaned the saddle mounting surface, mixed up some PC-7 epoxy and placed the saddle where it belonged. PC-7 is a relatively slow-curing epoxy that responds well to heat, so I put a heat lamp on it. Here’s a photo of the saddle after the PC-7 had cured and I had cleaned up the area.
More photos in the next post.