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On30 Underframe Options (Home)
Our On30 cars are designed to fit either our own original recipe Resin Underframe or the Bachmann®
#29907 Freight Car Underframe. The differences are explained below:
Our original Resin Underframe resin frame is closely patterned after plans for SPng boxcar #10 published in the Jan/Feb 2001 issue of the Narrow Gauge and Short Line Gazette. It is more typical of something running on a Western road from about the 1890s and later. The 4 trussrods and longer queenposts give the car a load rating of perhaps as much as 40,000 lbs. It comes with a Westinghouse Air Brake system consisting of the cylinder/reservoir, levers, and piping. (See information about Brakes below). The Resin Underframe consists of a one-piece Floor with all the sills (beams) cast into place. Styrene Needle beams are provided, to which Queenposts must be attached. We supply an alignment jig to make this task relatively easy. The Brake parts are from Grandt Line, and are highly detailed. Body bolsters with kingpins are separate resin parts as are the coupler mounts. (For conversion to On3, omit the coupler mounts. Attach Kadee® #803 couplers directly to the bottom of the Underframe.) The Trussrods are pre-cut and pre-bent for you. Holes for Truck and Coupler mounting are pre-drilled and (where applicable), tapped.
The unpainted frame reveals the different detail parts.
Note: the inside of the lower carbody should be painted before installing the underframe (unlike the
photo above, which was done in a hurry)!
Assembly of our Resin Underframe takes more time, but is not difficult.
The Bachmann® Underframe, having only two truss rods and short queenposts would be typical of a car with about a 20,000 lb capacity. It comes with an Eames Vacuum Brake Diaphragm, but no piping and only one lever (See information about Brakes below). The Bachmann® Underframe comes pretty much assembled and including couplers, which make it trickier to package. We provide a Resin Floor for use with the Bachmann® Underframe. The floor is held in the carbody the same way as our own Resin Underframe. The Bachmann® Underframe is secured the same way it is held into Bachmann® cars (via the truck mounting screws). So, their Underframe is removable (which is a good thing - you may want to convert the Brake System later when our Air Brake Conversion Kit becomes available).
Bachmann® Underframe shown with our floor. Note, the tabs on our floor are the same as on our Resin Underframe, and lock it into the carbody.
This unpainted view shows the Bachmann® Underframe resting in the carbody. It is held in place by the truck mounting screws. The couplers are included.
Concerning Brakes...
Air Brakes: Though refined over the years, the basic concept of Westinghouse Air Brakes is still used today. A reservoir on each car supplies air to the cylinder through a "Triple Valve". Loss of pressure in the "Train Line" causes the brakes to be applied. This provides a near failsafe situation should a train become uncoupled. While an Air Compressor has more moving parts than a Vacuum Venturi, compressed air is easier to deliver to where the work needs to be done than vacuum (which isn't really "delivered". Vacuum requires that air be pulled from the train. In the truest sense, vacuum brakes really do suck). Higher mechanical forces can also be achieved with compressed air, which is beneficial for stopping heavier cars.
Vacuum Brakes: Vacuum brakes relied on vacuum created by a steam operated venturi in the locomotive. Due to the accumulation of vacuum leaks in the "Train Line", longer trains were difficult to stop. With higher forces available when using compressed air, vacuum brakes were not widely used. The Sandy River & Rangely Lakes continued to use vacuum brakes up to about 1915.
We plan to release an Air Brake conversion kit for Bachmann® Underframes sometime in 2009.
For On30 Reefers click HERE
For On30 Boxcars clidk HERE