I wish I could take credit for this idea but I can't... all the credit goes to a guy named Gary. The following is the original information from Gary followed by a pictures which I took.
I have designed my track to have a 1" border all the way around. I was stuck at first how I would draw this border on to the timber so as to cut it out exactly to suit all the different radiuses of bends.
I came up with what I thought was a good idea which I would like to share with you.
I found a 2" metal disk and drilled a small hole in the middle of this. I then laid the track down on top of the timber and rolled the disk against the edge of the track with a pencil in the small hole. This gave me a very precise line 1" from the track edge. As I said I used a metal disk, you could just as easy use a jam jar lid as long as its diameter is 2x your boarder size
I used wood instead of metal.