K-Line K-0750 is what diameter?

K-0750 may be the manufacturer number. Check out this retailer. Does not have your number but some large radius K-line track.

I have lots of K-Line catalogs from 1987 up through 2005.  Not sure I have all of them. I looked through about 20 of them and the number K-0750 is not listed among the available track products in any of them.  The closest is a #K-0720 which started appearing in about 2003 and was still in the 2005 catalog.  But as you already know is 81” diameter Super Snap curved track.  They seem to have skipped all the numbers between K-0739 and K-0751.   

You said yours was Shadow Rail but the Shadow Rail used K-06XX numbers while the K-07XX numbers are for Super Snap.    

HTH,

Bill

"I suppose I could pick it all up, make a circle, and measure it..."

You could, but it would probably be easier to put one section of track on a photocopier, and shoot 12 or 16 images. Then tape the images together in a circle.

Or place the section on a large flat surface, like the floor, and shoot a line from each end, parallel to the last tie at each end, and extend those two lines to a point. Then measure the length of the lines at the point where they meet. That is your radius.

A carpenter's laser would be helpful, if you don't want to draw lines with a pencil on your floor.

Thanks gents!

It is for sure Shadow Rail and not SuperSnap. A mistake in the mold would make the most sense. Not at home at the moment but for sure some source had O-80 and another have O-81.

Actually I got side tracked by another issue; for some reason something that fits fine on the floor, two ovals of O-72 with straights, is not working in SCARM.

I might just break down and take the track up; but I need to find a place to put all the trains; some of the track is under shelves.

Both Legacy K-Line Trains and RR-Track  only show 081, 096 and 0120 sizes. That's to the center rail.

Do the geometry as Mr. Bloom has outlined and confirm the radius with the one piece. 

Regardless, in SCARM use the Atlas 3 rail O scale track system, which closely matches the K-Line, using 081. (Ross has 096 and 0120) You'll be missing some short straights, which you can make using the flex track modeler, then copy , paste and move if you need another. Change between Ross and Atlas libraries for the smaller radius curves to match the K-line radius. Switches will be another adventure. if you are using K-Line.

If that doesn't work, the basic RR-Track has the exact library and you may have to purchase that software.