What diameter Atlas O 3 rail track do I need for the outer track on a two track curve when the inside track is O-72. I need proper clearance for large articulated engines.
Original Post
Replies sorted oldest to newest
Terry L posted:What diameter Atlas O 3 rail track do I need for the outer track on a two track curve when the inside track is O-72. I need proper clearance for large articulated engines.
Terry: It depends on how far the engines extend out...80 diameter would give a four inch spacing...that MAY be good enough, but I have doubts. I suggest you draw arcs of 72, 80, 88, 96 and center your engines on these arcs to see if they would pass one another. My largest engine is a scale MTH 4-8-4 and will pass by 21 inch long passenger cars on 96 and 89 diameter curves.
And, I greatly prefer using flex track that may be bent to any desired radius/diameter...real railroads use 14 foot spacing which is 3.5 inches in O scale---very close---would only do that on straight track. 4 inch spacing is what I set my curves of 96 and 89 at. I do NOT have challengers or big boys...
You should be able to use O81. That will give you 4.5" spacing. Still, you always want to check those autoracks and 80' passenger cars against your big diesels.
Jan
It may depend on the placement of the curve. We had a place on the G&O where we needed 6 inch spacing to account for the boiler swing of a Big Boy using O-72 track. You might think today that you never will operate such large equipment. However, most of us have found that just isn't true. 4.5 inches spacing should work in most circumstances. As Jan said above, O-81 will give you 4.5 inch spacing using Atlas track.
NH Joe
Thanks, I am running a scale Cab forward so I need to play it safe. I assume that 0-72 and 0-81 will work if I just start the outer curve a little later. I'm only doing 90 degree corners so it won't have a chance to get too tight before it straightens out.
You might want to consider a section of 0-90 curve track leading into your 0-81 curves to give you the extra "elbow room" while providing a kind of easement or transition curve.
Is atlas curved track diameter measured from the inside, center or outside rail?
Atlas track diameter is measured from the center rails. You are right that you can start the O-81 curve a little later and increase the spacing. For example, if you want 5.5" spacing you would start the O-81 about 1" past the O-72. The tracks won't be exactly parallel throughout the curve, but they will be close. There is a free layout planning software program called SCARM that you can use to try out different configurations. It has a "ruler" function that will allow you to measure the spacing between tracks at any point.
