29 June 2010
This time, I decided to try something different. Instead of using double-sided foam tape, as I have consistently in the past, I went with an adhesive. It's my preferred home improvement product: Loctite PowerGrab. I simply applied a bead of it to the base, and dropped the track on top.
As I pressed the track into the adhesive, I suddenly realized that this might have been a huge mistake; I'd completely forgotten about all of the little slots and holes around the track joiners, and suddenly I was faced with growing white snakes and blobs everywhere. Yikes!
But what I thought at first was a major lapse in judgment turned out to be a golden opportunity. Using a moistened paper towel, I wiped away the globs, and the adhesive neatly filled in all of the cracks and crevices around the joints. Since everything will be painted, the remaining excess adhesive was the opposite of a problem; it was instead a cosmetic benefit.
Such is the beauty of taking risks. Sometimes, instead of just learning from our mistakes, we may occasionally discover exciting new possibilities we hadn't anticipated. And now my layout is ready for track painting. (PowerGrab is not a silicone-based caulk, so paint will adhere to it.)
By the way, I'm now really glad I decided to solder all of the track joints!
27 June 2010
Just making the plastic fulcrum piece, though, was quite an ordeal. I can't recall ever investing so much time in making a single little styrene rectangle—well over an hour spent on something that measures all of about a half inch long by 90 thousandths at the wide end, tapering to 40 thousandths at the other end.
Most of the work went into figuring out exactly how it had to be shaped. You see, it needed to hold a point rail such that each end was in precise contact with both the stock rail and the frog at the same time. Then it had to be able to rotate a degree or two and place the other point rail in precise contact at both ends. That's four precision points to hit on a moving part. That's hard work. Not to mention that one edge had to be ever so slightly curved for the diverging route point.
As for its fabrication, it was a relatively simple—if time-consuming—process of taking a few swipes with a fingernail file, measuring, test fitting, and repeating these steps countless times. And for all of that effort, the part couldn't be more uninteresting-looking:
And that was just the half of it. The following hour was spent attaching the points to the fulcrum. For this step I arranged a vaguely Rube Goldberg-ish looking contraption, with clamping tweezers clamped in a vice—plus a ruler thrown in so that the cork backing would make up for the difference in the sizes of the tweezer handles. Once I had this kluge jig set up, the real time-sucking work began as I had to measure exactly where the points needed to be positioned relative to the fulcrum.
What made it so complicated was that the bottoms of the point rails did not sit flush with the bottom of the fulcrum. This was by design—I didn't want the point rails rubbing on the base of the switch. So, it was measure, tweak, measure, tweak, repeat, repeat, and then, after a swig of wine to calm the nerves, it was time to apply the CA.
CA can surprise you. It can bond some things furiously well, often when a super-bond isn't even needed. Other times it completely fails to bond at all—even on combinations of materials that had proved successful in the past. On this occasion, when I released the point assembly from the clamps, it just fell apart, as if I'd applied water instead of CA. (This product became famous under the trade name "Krazy Glue"—and an apt name it is.)
Time for Plan B. What was Plan B? Solder the points to a metal fulcrum, and pretend it's plastic. Actually, Plan B used to be my Plan A; I'd originally intended to make the points out of a single piece of metal to demonstrate how simply it could be manufactured. But the potential of shorting pushed me toward the more conservative design approach of electrically isolating the point rails by using a plastic fulcrum.
No matter; the switch would work either way, and assuming there's sufficient clearance for the wheel flanges, nothing bad will happen. (If it did, I could use the old fingernail polish trick to add a layer of insulation on the sides of the points.) Since I had a plastic pattern for a new metal fulcrum, the hard work was already done, and Plan B got going quickly.
To simplify the assembly, I used .010-inch thick nickel-silver, as this was the clearance between the bottoms of the point rails and the switch base. I could simply solder the points right to the surface of the nickel-silver, then trim the nickel-silver down flush to the sides of the points.
After soldering the parts together, I determined the precise center of rotation and drilled a hole in the fulcrum, then drilled the corresponding hole in the switch base. I tapped the hole in the fulcrum for a 00-90 screw, then made a bushing from a sliver of thin-walled brass tubing.
The flea-sized bushing (above, just to the left of the screw) was crucial to the proper functioning of the points: it provided a smooth bearing surface for the hole in the plastic base—as opposed to the screw threads—and also allowed the screw to be tightened without binding the mechanism.
With the points temporarily mounted, I marked the throwbar for the pin that would move the points. This was just a small square of plastic bonded to the throwbar.
After about two hours of fine-tuning, I was at last rewarded with a nicely-snapping set of switch points. At this point I covered the nickel-silver fulcrum with the original plastic one, which I'd sanded thinner to account for the thickness of the metal under it.
But enough about building the darned thing... how does it work—with trains? Ah, for that, you'll have to wait until the next installment. I'm a real stinker, aren't I?
26 June 2010
As I normally do at times like these, I started digging through my material supply drawers. Hmmm, nothing but nickel, brass and stainless steel. My junk parts drawers were likewise devoid of useful amounts of sheet steel. Out in the garage, there was plenty of steel—hinges, brackets and whatnot—but all uselessly thick.
So I made a trip to the local home improvement store, where I spent roughly an hour wandering up and down the aisles looking for inspiration. The closest I came to something suitable was a ten-foot-long strip of flashing. It was only three bucks, but I simply could not see buying ten feet of metal only to clip an inch off the end. And I had no need for flashing, so the rest would just clutter up the garage.
I'd invested roughly two hours of total time in my quest over the course of about two weeks. It was starting to get absurd. Then, somewhere along the line—I'm clueless as to what triggered the thought—it occurred to me: a tin can lid. And there in the bottom of the recycling bin was exactly what I needed. (I have no idea what the can contained, but I do know it was best by February 2013.)
As an aside, this little adventure took me back to my very earliest days as a model railroader—back to a time when scratchbuilders were creative and made structures out of cardstock removed from new shirts, or benchwork out of discarded pallets, or locomotive boilers out of... wait for it... old tin cans. It's been so long since I've had to think that far outside the box that I'd forgotten what it was like to be that resourceful. Embarrassing.
Anyway, it wasn't long before I'd sliced the can lid into long, slender rectangles, and sanded the edges true. The final shape I needed was a very narrow, stretched-out L, which I cut out of the rectangles with a jeweler's saw and cleaned up with jeweler's files.
Once I had the points whipped into shape and bent to fit the switch geometry, I was both elated and vexed. It was a thrill to see the parts fit with absolute perfection; in fact, they actually looked better than I'd expected.
At the same time, I had substantial doubts about how to attach them to the fulcrum. My plan up to this point was to bond them in slots cut in the top of a block of plastic. But seeing the finished parts in situ, I could tell there wouldn't be enough plastic left at the bottom of the slots to hold together. Nor would there be sufficient surface area to reliably bond the sides of the points to the plastic. I was looking at a situation where I'd probably have to solder something to the point parts to give the assembly enough strength to withstand operation.
This did not, however, diminish my hopes of it being "manufacturable" one single bit. There are manufacturing processes that I cannot reproduce by hand, but that would ensure a very strong and simple assembly—indeed, the new point design could be made in a manner substantially similar to how the points in Eishindo's switches are made now.
And so the assembly of my new "recycled" points into the final working part will wait for the next installment, so as to give me a chance to cogitate on the matter.
23 June 2010
In this image you'll see a penciled-in plus sign. This is the center of the fulcrum. It's location took me by surprise: it looks as if it's way too close to the point end of the switch. But, the mark is in fact the precise midpoint between the end of the points and the tip of the frog point, which constitutes the length of the movable portion, save for the wings on the sides of the frogs, which don't count.
The flipside doesn't look especially exciting at the moment, and this won't change much. Except for the fulcrum itself, which will poke through to the left of the cover plate (right of center), the underside of the switch will essentially remain the way it is now.
Basically this exercise has brought me back to a point just before I'd chopped the switch open, when it was all one solid piece; the difference, of course, is that there are no guard rails, frog wing rails, ties, or any other features. An alternative to what I've done would be to mill out all of the aforementioned stuff, leaving a featureless expanse of smooth plastic. Obviously, not having a mill, I've had to resort to other means.
This little adventure of mine is having the somewhat unfortunate effect of making me wish I was the product manager for this thing...
22 June 2010
I believe I've nailed the new throwbar design, which is cosmetically barely indistinguishable from the original, and functionally quite close as well. Basically, using a needle file, I've opened up the slot in which it moves to increase its travel, which now appears to have reached a range of motion adequate for the task of moving the new points—and without impinging on parallel track sections, as a bonus.
I also removed all of the pins from the throwbar that engaged the original points, and shortened the bottom cover plate.
These simple modifications all offer a number of advantages: they make use of existing parts, which moves me toward my goal much more quickly and easily. Plus, should Eishindo actually adopt the design change (although I hold zero expectations they ever will), it should help to keep retooling costs down, at least for these parts.
In the process of making these modifications, I discovered a minor design flaw in their existing product: the pins on the throw bar that engage the points are a thousandths of an inch or so too tall, and as such they catch the edges of the opening on the underside of the switch body, as shown below; this has the effect of making the throwbar harder to move. (Should Eishindo decide to stick with their original design, they'd at least improve functionality by either reducing the height of the throw bar pins or increasing the relief for them.)
One word of caution to adventurous modelers who may be inclined to tinker with their switches: note that the assembly screws are very nearly single-use. Once they're removed, re-threading them is a serious challenge owing to the fact that they're held in place—barely—by all of about one thread on the stumpy little screws. Turning them just a couple of degrees too far strips the threads in the plastic holes. This sure adds to the "fun" of modifying—or even just repairing—these switches!
Stay tuned for the continuing saga of the T Gauge switch rebuild.
12 June 2010
I was on the verge of soldering the two point parts together when it occurred to me that I was looking at a potential shorting issue. With the points electrically tied together, it meant that, being the same polarity, the backs of the wheels facing the point rail not in use would be of opposite polarity, and given the high variability in flange width, I foresaw an unfortunate situation (below). So, the points could not be made from a single piece of metal.
This was not the end of the earth; it simply required a bit more thought. If nothing else, this simplified the mechanism from the standpoint that the wiper parts to feed current to the points would go away (they had to anyway, because using PC board as a cover plate on the bottom, as I'd intended to do, was not an option owing to its thickness). But how to reliably power the point rails?
The answer was provided by Eishindo. The original point design (above), which uses magnets to hold the points in position, also appears to use the magnets to improve electrical contact with the stock rail—even though the points are uselessly short to provide much of an electrical performance advantage. They'd even gone to the trouble of gold-plating the points, so it seemed as though it might be a good conceptual starting point.
Introducing my new point design, version 2.0 (below). It consists of two pieces of thin gold-plated sheet steel, .040-inch-high, with small tabs embedded in a cast-on plastic fulcrum (similar to the way the existing points are manufactured—at right). The metal is thicker than the original parts for more rigidity. The extensions on the ends provide additional surface area for contact with the stock rail and existing magnet assembly for the best possible electrical conductivity, as well as to hold the points in position (doing away with the need for a mechanical indexing mechanism underneath). And with the points being isolated, the point rail not in use is electrically dead, eliminating the possibility of shorts.
The flat top of the fulcrum part may vary in length from the way it's drawn depending on how much of the point rails need to be embedded in order to maintain sufficient rigidity; it could run nearly the full length of the point assembly, although I think the ends of the point parts should have a bit of flexibility in order to provide the best possible mechanical contact with the stock rail and frog point.
The fulcrum may be secured to the base in a number of ways. One thought is simply a screw and washer; another might be to cast small triangular tabs on either side of a split fulcrum so that the point assembly simply snaps into the hole. The specific method employed is unimportant, and more dependent on manufacturing costs: the former approach is more labor-intensive to assemble, while the latter potentially changes the fulcrum mold from two parts to three.
Not shown in the illustration is the new throwbar, which simply has a block that extends up in between the point rails and presses on the inside surfaces to move them. This may or may not require lengthening the extension tabs at the ends of the points for more rigidity and to lower the throwbar block. The throwbar may also need to be relocated from its current position in order to give it more mechanical advantage and reduce its travel.
These details will be ironed out as I begin experimenting. Stay tuned for Part 3.