Build A Wood Caboose, PART 2
A step-by-step explanation of how and why
BY DAVE CUMMINS
LAST ISSUE WE assembled the cabin and the underframe of D&RGW caboose 0505, then joined them together. This time we'll add the truss rods, trucks, couplers, and paint.
WORKING TRUSS RODS
Truss rods on a wooden car perform the same work as an I-beam steel frame in a modern car. In a steel beam car the weight of the car, and its load, put the bottom flange under tension and the top flange in compression. On a wooden frame car the truss rod takes the tension and the wooden center sills take the compression. Truss rods were always steel because metal is very strong in tension and a tension member may be slim. A member in compression must be thick, so wood is a good choice. Those are simple engineering principles, just so you'll know the theory behind what we're about to build.
Modelers generally use three materials to represent model truss rods: Nylon line, cord such as twine, and brass rod. Cord tends to look fake. Nylon line is fine (tennis racket stringing material is the right size) but you must keep it taught to keep it straight.
I definitely prefer brass rod. You may thread and install it in essentially the same way as the steel rods on a real car. So you may adjust tension anytime. And since brass is metal, it is rugged. There is also an added benefit some modelers may forget to consider: When models are as large as 1:24 or 1:22.5 scale they become heavy and the engine actually must exert some strain to move a train. The strain transmits in from the coupler, through the car body, and back out the other coupler. With body mount couplers the tension load goes partly into the end sill because the coupler usually is at least partly attached to the end sill. The truss rods tie the end sills tightly to the rest of the body so the rods take the tension rather than the glued joints. To me, that is an important benefit.
The perfect size rod for 00-90 threads is .046-inch (scale 1 inch). On the other hand, if you prefer 0-80 threading as I do, .052 rod (scale 1 3/16 inches) is great. A thread table would tell you to use .056-inch rod for 0-80 threading but in keeping with the principle of using slimmer rather than fatter, I build my models with .052. It is close enough to take the threading and is a lot easier to work with because you need to remove less metal.
[Editor's note: The D&RGW actually used 1 1/8-inch diameter truss rods with a flare to 1 1/4-inches at the threaded ends. That makes Dave's .052-inch choice an excellent compromise.]
I suggest using metal turnbuckles without factory-made holes because the holes are often too big to thread to 0-80. You may then drill and tap to your own specifications. Be careful of the new whaite metal alloys. Alloy pieces used to take threads, but changes in environmental laws have forced changes in the alloys; they are now softer and tend to gum up the die. In my opinion, brass is the best material in spite of the higher cost.
Full-scale car builders threaded one end of the turnbuckle right handed and the other left handed. Theat way they could tighten the truss rods by rotating the turnbuckle. Right hand threads alone are fine for our purposes since we can use the end nuts to tighten the rods.
Prototype truss rods ran straight from the queen post to a casting on the top of the body bolster. A small set of internal rods ran across the car at the bolster to reinforce it.
Our wheels have greatly oversize flanges and we need a tremendous amount of truck swing because of the tight curves on model train layouts. So we will have to relocate the truss rods a little to get enough clearance.
Working with your choice of trucks and wheels, notice where the bend point will have to occur. Cut and glue pieces of lumber between the longitudinal frame members to make the bend come at the right place. If you try to stay as close as possible to the original you may have to cut away part of your lumber to give enough clearance. That's okay as long as enough wood remains to hold the rod.
Since the short internal truss is invisible, we have no need to build it. So start by threading the rod ends going into the turnbuckles. You will need a pliers with good teeth to hold the rod while working the die. An eighth-inch of thread should be enough. Using your full-size drawing corrected for the actual bend location, mark in the exact shape the rods must be. Then bend all eight rod pieces. Note that one truss rod on this car is lower than the rest, to clear the brake cylinder. It will require a special bend.
Assemble the four truss units. Drill clearance holes (.067-inch, a number 51 drill) in the end sills and the coupler mount.
Commercial three inch high queen posts are correct for this car. Epoxy them to the needle (queen post) beam. Then glue the beam to the frame. Do that as a separate assembly, and be careful to maintain correct and consistent truss rod spacing.
Now we're ready to install the rods. It gets a little tricky, so proceed carefully. Begin by putting the unit in proper position on the drawing and cut back the outboard ends, leaving about 1/4-inch on each.
Turn the car upside down and insert one rod end into the body hole from the inside. Work as much rod as possible out through that hole. Don't be afraid to make the rod bend a little. That will give you the best chance to get the other rod into its own hole. You may have to put a lot of curve into it but you won't hurt anything. Just be sure to hold the turnbuckle to so it does not bend. With the two ends in their holes and the rod in place on the queenposts, center the turnbuckle between the needle beams. Then shorten the ends a little more, leaving just enough length to accomodate the washer and nut. Thread it now, working the truss rod first one way, then the other, to allow room for the die work.
The last thing is to slip the washers on and run up the nuts. Tighten just enough to cinch the unit into the U-shaped depression at the end of the queenposts. Washers are round on some cars and square on others. 0505 had round washers. Either styrene or brass is a good material. Drill a clearance hole for the truss rod. My model got regular hex nuts. You might want to be more accurate and make your own square ones from brass. Use material at least .050-inch thick.
ALTERNATE METHOD OF MAKING TRUSS RODS
You may find it easier to use the nylon truss rod method. It is simpler in many ways but lacks the advantages of brass.
Cut eight blocks of wood wide enough to fit between the longitudinal frame members and the same height as those members. Drill each with a .052 hole through the center and parallel (not perpendicular) to the floor. Glue each block into place between the frame members and under the location of the body bolster (the part of the underframe where the truck screws in).
Tie a knot in a length of .052-inch diameter nylon line. Insert the untied end through the hole in one block and thread on a turnbuckle. Then run the line up over the queenposts and through the hole in the opposite block. Pull it taught, but not so tight it will bow the car, tie another knot, and snip off the excess on each end. Apply a drop of CA (superglue) to each hole, and the truss rod is done.
This method has some minor disadvantages. First, the space in the turnbuckle is not clear. Second, you lack the appearance of threads. Third, you lack the structural support of the brass rod method and, if you make the rods a little too short, they'll give the car a hump-back. Finally, the blocks under the body bolster must be strongly fastened to the frame because they'll be under constant stress and could come loose.
The advantages, of course, are the relative ease of construction and overall good looks.
TRUCKS AND COUPLERS
Since fitting trucks and couplers can vary so much depending on what equipment you use, you may have to devise your own solution to that part of the construction. But let's discuss the subject anyway; maybe we will clear away some problems.
Gary Raymond 1 1/32-inch metal wheels (the small, so-called "one-inch" size) are my standard for freight equipment. They substitute easily into most brands of trucks. But as luck would have it, not into the Ryan 3-foot 7-inch Rio Grande prototype, probably the best looking and most accurate for the caboose we are building. Some simple modifications both to the length of the axle and to the recesses behind the Ryan truck journal are necessary. A future article will tell how to make those modifications.
My caboose model has a rail-to-body dimension of .975-inch. That is different from the prototype (a scale 1.023 inches) and I did it deliberately to "hunker down" the car and add to that low-slung, narrow gauge look. Remember, our track is wider than three feet so some minor tinkering with dimensions may help recapture some of that "narrow-gaugey" look.
First we'll need a cabin-height gauge. Take a piece of scrap sheet and carefully make it as tall as your car height is to be. Label it so you don't cut it up for something else by mistake.
Measure the height of your truck bolsters (the "crossways" part of the truck with the screw-hole in it, holding the two sideframes together), including the thickness of any washers (recommended!). The difference between cabin height and truck bolster height is how thick you have to make the body bolster. I like to make mine a little wider than the truck bolster and taper it up to the sides. It really doesn't show (remember, it's underneath) so how you do it isn't critical. Be sure the bottom surface is flat and perfectly horizontal or the car will lean. If you have a problem it will be a lot easier to work it out now rather than later!
I use machine screws to attach trucks, using the biggest the bolster hole will allow, depending on the brand of truck. Whenever possible I like to ream the original hole out to give a tight fit to a 1/4-inch machine screw. The Ryan truck, however, only allow a Number 10 screw. This ream fit eliminates part of the car's side play.
The rest of the side play can be eliminated by back-filling the holes in the sideframes behind the truck journals or adding washers onto the axles.
I drill and tap the wood of the body bolster and center sill, insert the truck screw with nothing else to hold it, and have never had any problems. With body mount couplers there's little stress on the truck screw. If you're going to use truck mounted couplers you may wish to fix a nut in or on the center sill, because such couplers run all the operating strain through the truck screws.
After attaching the trucks, turn the car upside-down and set a piece of curved minimum radius track (also upside-down, of course) onto the wheels. This tells you immediately just where you need to make cut-outs on the longitudinal frame members to get enough truck swivel and flange clearance. To look right, mount the trucks the same distance in from the ends as the real one did.
Another personal preference: I use Kadee 820 body mount couplers. If you also decide to use body mount couplers you should fit them in place next. You will probably have to hog out some material to fit the coupler snugly up into the center and end sills. A good way to mark that is with a permanent gauge. Make it as tall as your standard distance from rail to top of coupler box. First use it to mark the end sill where the coupler needs to go, then as a check gauge while you remove enough material to allow the coupler box to mount at the correct height. Finally, mount the coupler with as many machine screws as it has holes for. Wood will hold those screws just fine.
It is possible that mounting the larger Kadee 830 couplers, or some other brand, could be difficult with the car as low as I built mine. The answer would be to build the car as high as the original by making a thicker body bolster. Similarly, truck mounted coupers may require you to jack up the car, too.
THE DRAFT GEAR CASTING
Prototype coupler boxes (the draft gear) are heavy steel castings. They extend the coupler out about six inches. The castings also serve as the end plate for the two center truss rods.
On the model we must represent this piece. I am unaware of a commercial casting for this part. [Editor's note: Shortline Foundry makes a D&RGW version in 1.22.5 scale either for truck-mounted or for body-mounted couplers; Ryan Equipment offers one for body-mounted Kadee 820 couplers as part of their new bolster kits in 1:24 scale.] In any event, it is a part you may have to design individually to your model depending on the particular coupler you use. The box you see in the photos was designed to fit my particular coupler.
With almost any type of truck-mount coupler you may need to eliminate entirely the portion of the box below the end sill to give clearance for coupler swing. Some box, at least, should be installed for visual effect.
As for materials, that's rather easy. I think styrene is by far the best choice. .060-inch sheet seems best to match the wall thicknesses of the original. In your design, try to incorporate the same rib arrangement as the original and almost any attempt will look believable.
Paint will help this piece a lot. Even if you airbrush everything it might be a good idea first to brush some paint into the corners to form fillets, better to imitate the original casting.
The Rio Grande used very distinctive steps on their end platforms. The model may follow the originals very closely for two reasons. First, Shortline Foundry makes correct steps in 1:22.5 scale and all you have to do is glue them on; second, if you choose to build them from scratch you'll require only two strips of brass or styrene. I prefer brass because the steps are the most likely part of the car to sustain damage in the event of a derailment. If you make 'em tough you won't have to do 'em all over again. [Editor's note: Shortline Foundry's castings are white metal and fairly rugged. Of course, if they bend or break, you may always buy another.]
Use .032-inch x 3/16-inch strip and, using two pliers, bend the main piece. Be consistent with both the height and the width. Then bend the back piece. Do it so as to make the back piece fit a bit snugly into the main piece. It will tend to stay in place and make soldering easier.
Sand the surfaces you will solder. Hold the assembly in a vice by the "attach tabs" while you do the soldering. I used escutcheon pins to attach my steps, so drilling those holes came next. Clean 'em and paint 'em and they're ready to go. [Editor's note: The correct color would be either boxcar red, black, white or aluminum depending on what era of the D&RGW you want to represent. Prior to the 1940s, black or boxcar red would be correct. Between about 1940 and 1950 the hardware was white. In the '50s the Rio Grande repainted end rails, steps, ladders, and grab irons an aluminum color.]
BRINGING THE PARTS TO LIFE
Here comes the fun part. Seeing parts of the caboose begin to look real as you add the color. In our case, painting subassemblies is almost a necessity. Otherwise it will be very difficult or impossible to do a neat job as we add the roof and the hardware.
At the very least we should paint the cabin before we epoxy in the glass windows. But we should leave a little unpainted surface where the epoxy will go so it can grab wood instead of paint. Touch it up afterwards.
The best way to color the platform floor boards is with a stain. They should look well-worn and mostly unpainted. Color them before installing them. Several methods work well, but all have one rule in common: Use a very dilute mixture. You may always add more, but you can never remove the stain once it's on. I have had best results with a mixture of a one or two drops of Floquil Grimy Black in a capful of their Diosol thinner. I have also found mixing a drop or two of black shoe leather dye or India ink in a capful of rubbing alcohol works quite well and helps to avoid both skin and respiratory contact with the dangerous chemicals and fumes common to laquer-based paints.
For paint you again have a few choices. The D&RGW used a shade of boxcar red slightly different from any commercially available model color so I mixed my own. The actual color is brown with a reddish cast. I used Pactra acrylic enamels (water-based and considerably less toxic than laquer-based paints), mixing six parts A14 Gloss Brown with one part A7 Insignia Gloss Red. That virtually duplicates the Rio Grande's color. If you want less shine, spray on Testor's Dullcote either from an aerosol can or, for a more professional result, from an airbrush.
Floquil Boxcar Red is also a good choice and you may buy it in spray cans. With a model as large as this it may be quicker and easier to paint from a can instead of using an airbrush.
And speaking of spraycans, Krylon Ruddy Brown Primer also produces a realistic and attractive oxide red color suitable for freight cars and cabooses.
Remember, these cars faded and railroads generally bought paint from the least expensive supplier so shades often varied considerably. Any of the shades I mentioned would probably be credible at any given time in the caboose's history.
I wanted to keep the underbody and inside of the cabin as unobtrusive as possible so I painted them flat black. On the prototype the interior is an "industrial" light green, sort of a "pea green"; the underframe is the same color as the exterior--boxcar red.
This installment ought to keep you busy through the holidays and into the new year. Next time we'll add the roof and more hardware.