We had a discussion of this issue a couple of years ago regarding the placement of my Walthers Cornerstone Modern Roundhouse relative to the Walthers Cornerstone 130’ turntable. Ed (7j43k) posted a formula in that thread which proved to be totally accurate. Here is that formula:
Based upon that formula, the exact distance of the roundhouse from the edge of the pit on the 90’ turntable would be 4.8125" (4 13/16 inches).
Rich
Edit Notes: The stall width is exactly 2" front, and 5" rear. The stall length is 17 5/8". The diameter of the pit is 13 3/16".
The (a-b) calculation gets you the effect of the stall angles. Or at least approximately. The formula provides a method of calculating the effect of the proportion of two hypotenuses: that of the right triangle within the roundhouse and the right triangle outside the roundhouse. The radius (d? not r?) of the turntable is then deducted from the length of the outside hypotenuse. Given the requirement for accurate track lengths I recommend using the cut to fit method instead.
All you really need is the two measurements: The distance from each of the two back corners of the side walls of the roundhouse to the point on the layout where those two distances meet. That’s the center of the turntable.
The depth of the roundhouse and the stall angles place the distance of the centre of the turntable to the back wall of the longest stall, which is the number you actually need to place the roundhouse. The length of the connecting tracks is then just a cut to fit problem.
As I tried to point out earlier, the real question to ask is where does the back wall of the roundhouse fit into the layout? The other dimensions all result from that point regardless of the size of the turntable.
Well, this is a lot of discussion for something so simple. The instructions I read were if you were using a **** size turntable install RH tracks so they stick out **** inches from the front edge of the roundhouse floor. That is what I did and the fit was perfect.
I am pretty sure it was the RH instructions that gave that but I no longer have them. I could be wrong and it may have been somewhere else I read it other than the instructions, but I don’t think so.
That would surprise me if the roundhouse instructions specified the distance because the radius of the turntable is part of the forumula, so the rounhouse specs would have to account for different size turntables such as 130’, 110’, 90’, etc.
You can’t find the instructions that you read and you don’t know where to find them. I looked at my instructions and template and there is no reference to distance specs.
So, apparently, it is not so simple.
But it doesn’t matter because once I printed Ed’s formula from my older thread, an exact distance was finally provided to the OP.
If the distance from the roundhouse to the turntable is long enough, you will get the tracks overlapping and there will be frogs in the approach tracks. Ashland, WI on the NP was one example of such, and there are others.
The footprint of the turntable and roundhouse are determined by the roundhouse stall angle and length. The turntable size is not relevant to the calculations you need to make. If the turntable needs to be (edit) smaller than ideal because the roundhouse stalls are very long or the operator wants long tracks in front of the roundhouse doors for some reason then connecting tracks could connect or cross, unless you also change the stall angle.
Put another way: you don’t need to know the length of the connecting tracks between the edge of the turntable and each roundhouse doorway. That number doesn’t help you locate or install the roundhouse and turntable.
You just cut those connecting tracks to fit after the roundhouse and turntable are in place just as you would for any layout.
No complex calculation is required. The roundhouse location determines where the center of the turntable must go which in turn requires a certain length of connecting tracks. You never need to calculate the length of those connecting tracks.
