I need to place my 90’ HO turntable inside a 22" radius mainline curve. To have room for the roundhouse, it needs to be as close to the mainline curve as possible. How much distance should I be looking at?
Which turntable are you using? The Atlas 3 stall & a Walthers with add-on stalls are way different![%-)]
Not that it makes any difference but I have a Walthers 3 stall kit. I want to leave as much room for it as I can.[sigh]
Do you have an NMRA clearance gauge? That would tell you in an instant. If not take the longest car that will go around the 22" curves and measure its overhang. Note this will be the dead center of the car. Add 1/4" to that and I would say this is the minimum distance for the roundhouse, turntable, or anything else to the track. This also assumes nothing on the turntable will ever “overhang” the end.
This engine is rounding the curve behind the Walthers roundhouse at the Bucyrus club…This area was finally fully scenic in November of last year.
That last sentence above is critical! If you are turning your NYC Niagara on a scale 100 foot turntable, the butt end of the tender will be sweeping an arc with a 120 foot radius! That’s why it was designed with that long rear overhang.
My advice is to take a piece of paper (I used card stock,) draw a circle the diameter of your turntable’s bridge length, then figure out how much overhang you will have to deal with when turning whatever overhangs the worst. Draw that overhang arc as a concentric circle, then bend a length of flex to 22 inch radius and see how close to the pit center you can move it before the center of your Pullman, auto rack or humongubox meets the arc of overhang. Add 1/4 inch so your little people don’t suffer heart attacks watching for a sideswipe.
Chuck (modeling Central Japan in September, 1964)
Bruce, figure on the lip edge plus one full inch, and add another 0.5" for any rolling stock passing by on the main longer than 70 scale feet.
-Crandell
I guess “far enough so there are no collisions” is about the best answer I can give!! If you can find a pic (like in one of Frank King’s books) of Endion MN on the DM&IR line, you can see that it was squeezed into a narrow area next to Lake Superior, between the Duluth-Two Harbors mainline and a road. The five-stall roundhouse was about as wide as the turntable, they had to increase the radius of the roundhouse’s curves or the ends would have been too wide, so the tracks curve coming off the turntable almost like they were going to a square enginehouse.