Car Frames - Keeping Trains on the Track
It is very important to have a frame that holds the track well, particularly with cars carrying passengers. Just follow a few simple rules and you'll cut down your derailments considerably.
Rule #1: Bolster plates must be level to each other
Some meets I have gone to, people approach me to trouble-shoot their
derailment problem. They begin by pointing out a track area, saying other
cars don’t derail there. So I check out the frame first.
It's easy to do. Turn the car over and remove both trucks. Wipe clean the
upper bolster plate (the surface which the truck bolts to). Take two levels
and place them on each plate, crossways to the car. They both should read
You can get by with only one level if you can guarantee the car does not
move when you check each plate.
Also, you should check to see that the bolster plates are level lengthwise.
You can do this by placing a piece of bar stock (that you know is straight)
on both bolster plates. The bar stock should sit squarely on BOTH plates.
I have also seen cars with a bent kingpin. These pins must be 90 degrees
to the plate in all directions. The truck should furthermore have a rocking
motion, but not too much. I limit mine to 1/32” for each bolster pad. I have
good results with this dimension coupled with a flat frame.
The following diagram shows the design I use. If possible, buy tubing with the seam on the small side. If this is not possible, then weld the upper bolster plate on the opposite side of the seam. In other words, put the seam on the top-side. This will insure level bolster plates.
Here's another drawing supplied by Tom Bee for those who want to build their own car frames.
Frame shown with car body removed
Rule #2: Place the load in the middle of the car and make it as low as possible.
If the load is on one truck only, then the load sway puts the bolsters out of
balance. The load compresses the springs on that truck only, causing the side
frame of the other truck to lift upward pulling the wheels off the track and
derailing. In this case there is nothing wrong with the track or the frame.
The "built-in twist" of each truck doesn't help this matter either, it's just
Rule #3: Put coupler height in proper dimensions.
I have actually seen one coupler move under the other, lifting the car off
the track. Follow the IBLS standards and make the middle of the coupler
pocket 4 5/16" to top-of-rail while the car (or locomotive) is loaded.
Typically, loaded cars from unloaded cars move 1/8". Which means for
cars carrying passengers or ballast, make the coupler centerline 4 7/16".