Jeff, Perhaps if you gave us a few dimensions and info such as what model carriage, what scale carriage /gun including length, width and height of rails your Chassis will have, we could all visualize what size Barbette Carriage you want to make. It would also help Austin out by telling him if his mill has the capacity to do the work. We know a little about the process having built a batch of the 100 Pdr. Parrott Seacoast and Navy Rifles upon such a carriage. FYI, we are Not looking for this type of work.
Looking at the photo we took of the 1859 iron, front pintle carriage below, you can see why all of our searching for ready made, scale I-Beams was for naught! Nothing, not even British garden railway I-Beams were the correct size for a 1/6 scale carriage. We needed 28 inch long, 2 inch high and 1 inch wide I-Beams with 15 degree gussets 4X. The big problem was that the web (vertical part) was only .200" in 1/6 scale. All the webs on existing beams were Much thicker! Making them
was not fun. They were just about 2" outside the capability of our Bridgeport Series 1 milling machine. We built a gigantic shuffling fixture, a 70 pound device which held the 1x2x28" bar of 1018 steel, and after we got to about 50 % of total length milled, we shuffled the bar down about 3 inches and milled the other half. The other 4 sets were farmed out to a local shop with larger mills. We absolutely stole those rails from them at 250 dollars per set. They told us weeks later that the owner's brother had goofed up the bid and they should have gotten 400 dollars per set! He was too embarrassed to ask us for more money. They also had to meet the .015" we specified for straightness in the 28" length. Lots of arbor press time there!
If there is anyway that two pieces of small U-Channel can be welded together would satisfy your requirements, then a rail set will be a heck of a lot cheaper. Anyway, Good Luck! Can't wait to see some build pics!
Tracy and Mike
Fort Pulaski, Georgia...End of the Chassis upon which the upper carriage slides. Carriage for a 100 Pdr. Parrott or a 10" Rodman Gun.