Marvelous work! That 2-6-6-2 is the 'cat's meow'!
How do you join the frame pieces together? AND the boilers?
Thanks! With the articulated it is just a matter of making a brass extension to the rear of the front engine, and making a pivot with a piece of brass tubing and a screw. On an earlier one, the boiler was simply the plastic prairies cut and cemented together. The one shown is actually a couple of Pacific boilers that follow the same method as with the rigid-frame locomotives: On those, I locate where I want to cut the two halves of the frames and the boilers, based on the length of the additional side rods to be added to the driver sets. Fortunately, Mantua side rods are separate pieces, not one continuous piece like some other makes. The ends overlap and the hex-head screws have shoulders on them that allow the two pieces to pivot up and down slightly. This is handy for one of the things I do to allow the longer wheelbase to negotiate 18" radius curves.
When I am sure where to cut the frames, I splice the cuts with a new cover plate made out of brass with the additional screw holes located and drilled. I might make another splice plate to go on the top side of the frame, but haven't really found it necessary, as the boiler keeps the frame rigid.
For the boilers, I make the cuts for the two pieces using a very precision method...stick each original boiler in my bench vise, leave a little extra that can be filed to fit, and grab my hacksaw! I'll screw each piece to the frame, filing the joint until they fit snugly together, then take them off and drill a small hole in the ends of each side of one piece the right diameter to hold a small nail with the head cut off. The trick on the second piece is to drill a slightly larger hole for the other end of the nail so you don't have to be quite as precise in locating the matching hole. Then, I mix up some two-part epoxy, preferably some that has metal particles in the matrix. Devcon Plastic Steel is what I used for the first ones. JB Weld is also fine. Pack the epoxy into the holes where the nails go and along the mating faces. I then screw the boiler to the frame and let the epoxy harden for at least 24-48 hours. Then, file and sand the outside of the joint, and add whatever details I want.
Now for the dirty little secret on how to get a 2-10-4 around an 18" curve: Turn the locomotive on its back. Remove the cover plate. All but the earliest Mantua's have brass bearing inserts that the axles ride on. Remove the front and rear drivers and their bearing. Cut a small strip of .010" brass sheet that fits in the slot in the frame. There is a locating pin that keeps the bearing from sliding around, so you have to make a hole in the strip. Place the strip in the slot over the pin and put the bearing and the driver back. Now make a piece of brass that will go over the middle drivers, leaving a slot for the drive gear. Drill holes where appropriate to accomodate the screws that hold the main cover plate. The end (flanged) drivers are now shimmed downward .010", while the center driver are shimmed up off the rails .010". The purpose of this is to prevent the blind drivers from catching on the railheads as the locomotive come out of the curves. You can't tell the blind drivers aren't resting on the rails unless you get right down at eye level with a light behind the locomotive! With a gearbox and a can or coreless motor and driveshaft replacing (unless one of the original engines came with it instead of the direct drive open-frame motors), the weight of these beasts is sufficient to pull a bunch of cars up a 2-1/2 percent grade with curves at each end.
For my B-1a Mountain 4-8-2, I just used a Mikado frame and spliced on the front end of a Pacific. The boiler is made from two Pacific's.
Hope this longwinded explanation isn't too much for the forum. The main problem nowadays is that the components are getting scarcer and most expensive. I just paid $30 plus shipping for a plastic pilot without the air pump shields cast on! (The "Q" mounted their cross-compound compressors under the walks. WARNING! Following the above procedures could be HABIT-FORMING!