Eltham Model Railway Club
Ideas and Help - Curve Tolerance
It's very simple really. your curves, be it a yard on a curve, a doubletrack mainline etc- you have to allow a clearance factor so your trains do not hit when passing on a curve ! Rather than finding out before making and laying your track, it is best to plan beforehand. To do this simply find the longest item of rollingstock that also has the lonest overhang, ie a long wagon that also has it's bogies well back, so when going aorund a curve, it swings out more. A long loco is also a good thing to try. A Big Boy articualted steam monster loco is another.
To test and ensure you do not sideswipe a train when passing, simply draw out a curve, the tighest you wish, then draw a parrallel arc/curve at the next radius you propose to use. I used a stick screwed to a wood and a hole up the other end for the pencil. To change radouss I drille more holes to repositon the screw rathe rthen the pencil. You then simply place your rollingstock onto the paper to compare and see the tolerances and clearances. It is good to have say three items of the same wagon, but you can mark the clearance points as well.
The pictures show me doing this very thing to test some ideas I have for out exhibition layout. THe inner curve is 30 inches, our absolute minimum radius. On straights we use 45mm track centers. But for such a sharp curve we wan to allow a wider track center to allow for wagon and loco swing. In this test I set two track centers, 55mm & 65mm. I tested the closer tolerance first with my longest wagons - 80ft container wagons. - they passed with flying colours. Yes they could get a little closer, but we have a margin here for error and longer & wider locos/wagons.
