Mr. Edmund Collins III was kind enough to publish the plans for the 30,000 lb capacity flat car in the book Hidden Treasures: The Story of the Ohio River & Western Railway by Ed Cass which was published by TimberTimes. I highly encourage subscribing to their magazine if you like logging. It is quite excellent!
With these plans we can build the car. But I like to have assembly drawings for construction. The difference is that Collins' plan is not to scale. I want to build an O scale (1/4" to the foot or 1:48th) model and will need to know what length to cut the wood. Construction drawing are not as detailed and are based on building sub assemblies.
First we'll need the frame. It consists of two end cabs made of wood, and six beams. There are two needle beams as well. For the NMRA AP Judging you don't have to use a CAD system. I just use it because it is faster.
Next I label the drawing with its pertinent information.
To start the drawing I'll start with my best know timber dimension which is the end cap. Right away I spot a mistake in the Collins drawing. The top drawing has a square timber cap but the frame drawing below has a not that it is a 6 x 8 cap. Problemo!!! The photos are very hard to make a call from. Other wood flats that I've seen appear to have something closer to a 6"x8" cap than an 8" x 8" cap so we'll go with a 6"x8" cap.
30' less two 6" beams yields 29'. That is the length of the beams. The drawing says they are 5 x 12 inch on the outside beams. 5 x 8 on the four inside beams. Normally they would be interlocked with the cap in some fashion, usually with the beam with a notch that the cap fits in, but that doesn't seem to be how this car is built per the photo showing the straight on shot of the end cap. Maybe it was notched in the end cap in a mortise type arrangement.
Let's start building our grocery list for lumber. To convert the standard dimension to O scale dimensions we'll use my grid located here: http://modelrailroadersnotebook.blogspot.com/2010/02/o-scale-lumber-converters-tables.html. You can also use this site: http://urbaneagle.com/data/RRconvcharts.html. We'll start with the 6" x 8" cap timbers. 6" / 48 = 0.125, which converts to an actual 1/8". 8" / 48 = 0.1667, which converts to approximately 3/16". I'm not going to buy scale lumber for this model but I might have something close. So I'll sand or saw the wood to the precise measurement.