using 1"x 3" tubing for car spines?

[DRS_RR]

I know one of the limiting factors for a tighter radius track like I have at home is to ensure that you have enough swing in the coupler pocket. I was looking at the recent cars added to DSL that are for sale, and looking at them it appears they too were built with a 1"x 3" tube for the spine and don't look too bad. I know there are the drawings of the Tom Bee splines for 1"x 2" tubes, I haven't seen any for a 1"x 3" tube. If I went with a 1"x 3" tube does the bolster plate need to be made wider also to all for the sharper curve for the trucks to make contact with? plans call out for 2" should it be wider like 2.5" or 3"? Unfortunately I'm limited to 23' radius in the backyard and that is what I'm stuck with, the cars I have now have the cannonball wide coupler pocket on it while the engines have the normal coupler pocket and seem to do ok together, but I'm afraid new longer cars might cause issues so thinking the wider tube might be a good compromise.

Another question I have is I know Mike Massee in his builds that are posted on here uses this set up where he welds a section of tubing on each side for the bolster plate instead of having the 3/8" plate for the bolster plate added. I'm not sure if this is due to the type of trucks, or since he is modeling in larger scale with trucks with larger wheel sets it sets his coupler height? If there are any advantages/disadvantages from just welding tubes on the side for the bolster plate.

I also like how mike had angles welded to the sides of the spine for mounting to the wood car bodies.

I found a decent trailer shop and the guy said he can cut and weld me up some frames at what I consider a decent price since I don't have the ability, but figure I should get some questions answered first so that when I do this I'm not left with junk that can't be used.

Any input and suggestions are welcomed.

Thanks,
Dave

[rkcarguy]

1x3 tubes will certainly allow more pivot of the couplers, but also where the hole is drilled in the coupler and placed in the end of the tube has a notable effect and 1x2 may still be plenty. I used Tom Bee couplers, and drilled the couplers on the dimple provided. Then I drilled the holes through my 1x2 tubes 1-1/8" on center from the end and it seems like about twice as much side-to-side movement as I'll need for a 40' radius.
As for frame design and ride height, there are different truck manufacturers with different heights, and a lot of variance there. I tend to try to make my stuff as low profile as I can, so I can always add spacers to get the ride/coupler height correct.
If you look at pictures of rolling stock online, many 40' flats, bulkhead flats, and tank cars have the trucks nearly at the ends of the frame so the wheels are barely under the end of the car. This is good, because it means less frame "cantilevered" out over the truck bolsters on curves and less coupler pivot required. Not sure what you are wanting to build, but that's something to consider.
I'm building in 2" scale and fabricate my own frames, I use channel or tubes for the spine, angle around the perimeter, and smaller channels spanning from the spine to angles on the sides. The angle and channel provides many areas to drill through for attaching the deck. Where the channels may interfere with the trucks/wheels on the ends, I use flat bar there instead.
One word of advice, the side you weld will shrink and pull things out of plumb. So you always want to try to weld the same on both sides and top bottom so you don't warp your tube. I don't like welding angle along tube, because it creates a lap seam which cannot be painted and will ooze rust.

[Glenn Brooks]

Dave, you are on the right track identifying coupler pockets as a principle limitation for tight radius curves. Fortunately you don’t need any coupler pocket at all to make 7.5” gauge cars serviceable. Just attach an appropriately long shank from the coupler to an attachment point at or near the sill, or inside the frame and you’ll be good to go. Add coil spring to the shank, both sides of the attachment point if you want to buffer coupler shock. Any car up to 3” scale will swing a 23’ curvature, if the couplers are not limited by a pocket assembly. In fact I’ve seen lots of 1:1 flat cars, RR rcranes, and other MOW rolling stock with no coupler pockets at all- just a proper draft gear attached to the inner most joists, or beams of the frame.

Which leads to one other observation. The ”spline” you commonly see on 1.6” car builds, works very well for live steam rollingnstock. However, it was never a solid one piece beam on 1:1 equipment. In fact, flat car builds all had up to 6 joists evenly spaced between the end sills to form the car frame. The center bit was usually never solid. Always the inner most beam was actually a two piece assembly - left and right hand beams with draft gear mounted in between, on the center line.

To achieve freely turning trucks on your build, you can affix a bolster plate across the width of the frame. Drill a hole on centerline and drop a pin down through the bolster and thru the truck bearing. Good to go.

Here’s a similar example. Now this is a 12” gauge 3” scale flat car (built with 1x3” tubing). It has a 3” king pin and bearing pocket arrangement, mostly because I wanted to build this true to the original 1885 bolster design as possible. However a simple 3/4” diameter bolt would have done the trick as well.

PS. 3/4” x2” channel works real well for car frames as well. Channel and I beam shapes were the actual materials car builders used for frames in the steel car era.

You could also go for true miniature quality and build wood frame, truss rod flat cars with simple wood working hand tools and a pot of glue! harlock has a superb wood frame car build here on Chaski that gives plenty of tips about technique.

Good luck. And have fun! Building rolling stock is a fascinating thing to do.

Glenn