Posted 25 October 2010 - 03:53 PM
For a trailer frame, 2" x 2" square tubing should be just fine. In 1/25 scale, this would translate to .080" square strip. For an older drag car frame using rectangular tubing, 2" x 3" was often used, which translates to .080" x .125". If you are building frame rails that kick up at the front and/or rear, consider using .080" thick sheet plastic. You would then cut the rails out as one piece with the kickups built in, which would save time and save a lot of angle cuts. The leftover pieces could be cut into .125" strips and used to build crossmembers, traction bars, etc. To build two matching rails, cut the two pieces out, tack them together in a few spots (not too many) with super glue, then finish shaping them while they are together. When you are done filing them to shape, separate the two pieces with a single-edge razor blade and scrape/sand off the glue. A trailer frame would normally be built to allow for a flat floor, so you don't need to worry about kickups. Straight strip material should work for that.
For a trailer axle (or a drag car straight tubular axle), don't use styrene rod. Instead, use 3/32" styrene tube with .039" music wire inside. The styrene rod will sag or bend under the weight of a finished model (even a trailer). The music wire, though difficult to cut, will not bend. If you use regular model kit wheel backs that are made for the usual model kit wire axles, you will have to plug the axle holes and redrill them smaller for the music wire. Don't use larger styrene tube with a regular model kit wire axle inside unless you are constructing a trailer to haul a car on. In that case, you'd probably use larger styrene channel or I-beam to build the trailer frame too.