Question About Track Curve Sharpness

[waycoolratt]

I bought two Athearn Western Maryland SD40 locomotives today, I plan on starting my portable layout soon. I'll probably make it in 2x3 and 3x3 sections that I can take apart when I need to move it. For this project, the sharper the curves in the track, the better so I can save space. When I was a kid the layout my dad built had a curve that would derail some of the locomotives that have 3 sets of wheels on each truck, my two newest obviously being SD40 have 3 sets on each truck.

I'm wondering how sharp the curves can be and still almost gaurentee they wont be regular spots that derail the locomotives. Does anyone have any suggestions?

 

[UP2CSX]

Well, I can guarantee they won't derail on 36" curves. Unfortunately, that's not an option for you. The absolute minimum with perfectly laid track would 18" curves. 22" curves, again well laid, should be fine. In many cases, the absolute radius of the curve is not as important as the track being prefectly level and the arc be smooth, with no kinks or bumps, especially at joints. This is one situation where flex track may be the best solution since you can lay the largest curve your layout section can accept, which may be a little bigger than you'd get with sectional track.

 

[lmackattack]

minimum 18" if track is near perfect
22" is better but will still look a little tight

26"+ would be best if you hav the space

also Number 6 switches is a sugested min for 6 axel locos

 

[Cjcrescent]

A picture is worth a thousand words. Jim was right when he said that 36" radius won't work.

However, you can get pretty close! Attached is a quick drawing I did in Xtrkcad, showing the minimum and max radii you can fit on two, 2x3 foot modules for a corner. A 3x3 module really wouldn't be different. The smallest two radii are 18" and 20". The largest is 34". Depending on where you have your track locations, as well as the overall size you can build for, you can go from 18" to 34" or anywhere in between pretty easily on your corners, and not have to worry about derailments. If/when it comes time to move them, just take a dremel tool and slice the rail at the joints!

All this is assuming that you want to keep your curves on two modules. If you want to keep them on one module only, then you will be limited to a max of 22"

 

[Selector]

Although, if you intend to have a closed loop of any configuration in your defined space, you will have to have curves in the 18-22" range on the face of it. The more folded and convoluted your loop, expect much tighter curves than 18".

Essentially, you take your widest distances where you know you'll have the tracks doing a 180 deg to run back to close the loop...whatever shape that loop is (oval, figure 8, etc.) That widest distance must accommodate tracks that have curves measured at the centerline! That means a couple of things: the outer rail on the curve will go wider than the centerline, so plan for that, and secondly, you should have about 2", minimum, outboard "terrain" outside of the ties along those curves so that tumbling engines stand a chance. If you can't do the 2" because you need the wider curves, then glue a 1" tall retaining object, like a retaining wall or a rock cut at the edge to catch falling rolling stock or engines. Mind the clearances! How much overhang outside the outer rail will your engines have on your tight curves? A steamer is likely to need about 3/4" clearance for the rear cab roof and other parts of it on tight curves.

But, for figuring, rough figuring, you take your widest measure through the curve and divide it by two. That will give you your centerline radius. For a sheet of plywood, that is about 22" safely with some terrain outside the curve for placement of something to keep engines from falling off the edge.