This forum is dedicated to Riding Scale Railroading with propulsion using other than steam (Hydraulics, diesel engines, gas engines, electric motors, hybrid etc.)
Hi all,
I have a small 0-4-2 porter type loco in 4 ¾ “ gauge that can negotiate 7.5’ radius curves. What in your opinion is the tightest turn that can be made in 7.5” gauge with a locomotive that is 13” between wheels? How much will increasing the gauge in the curve help?
I’m hoping to run this thing in my small back yard and was hoping that one of you could chime in with some suggestions.
Joel
Photo below is my 4/ ¾ “ gauge loco on a 15 foot diameter temporary track.
RJ
You're probably going to get more wear on the track and wheels on really sharp curves, but it should work. Widening the gauge is also good up to a point (perhaps adding 1/8"). Slow speeds are in order, and maybe a little oil on the outside rail (assuming little or no grades).
Just for fun, have a look at the prototype specs on the electric loco I am building. First a picture from the Davenport catalog (1937). Second picture is a blow up of the Davenport specs, listing the minimum radius of 25 feet! With 2.5" scale, that would be 5.2 feet minimum radius! Actually I don't think it would work because my lead truck doesn't have enough swing. The last picture is my engine, not yet finished. Its rigid wheelbase (distance between center lines of drivers) is also 13".
Short radius curves are ALWAYS a trade off. While the gauge and scale are different, our experience is the same. With our home made train, 18" gauge, 3" scale, we are running 12' radius curves. Wheel and rail wear are obvious. Two things that often get overlooked: Power & Bearings. The short curves take a lot of power to get through, even with expanded gauge. In our case, the 5 hp Briggs & Stratton, geared down three times, has plenty of power to get around. With the smaller battery powered locos, using the extra power will shorten your riding time. Maybe significantly, maybe not, but something to consider. While doing some maintenance, I noticed what seemed to be extra side play in an axle. Further testing noted that all of the axles appeared to have more side play in them than I remembered. Upon detailed investigation, I found the brass insides of the axle pillow block bearings had been worn away by the shoulders on the axles. This is what is allowing the axles to slide side to side farther than original. This lateral wear is caused by the force exerted, on the axles, in the curves.
You have to remember, I didn't build the train and I would not have placed sliding pillow block bearings on the axles, where the axle is allowed to slide through the center bearing race, being located by the shoulders on the axle. But this does illustrate the little seen effects of short radius curves.
As I said, short radius curves are ALWAYS a trade off. Shorter equals more wear, more power needed, but allows for more right of way options. Larger equals less wear, less power needed, but reduces your track laying options. Just some thoughts to keep in mind.
With 2.5" scale, that would be 5.2 feet minimum radius! Actually I don't think it would work because my lead truck doesn't have enough swing. The last picture is my engine, not yet finished. Its rigid wheelbase (distance between center lines of drivers) is also 13".
