Do you mean a circle within a circle?
Some added information that I sent to another forum.
I am including my questions and their answers. Maybe you can help answer my unanswered questions.
Questions
I only have a 44" x 20" space to work it. I would like to make a figure 8 in that space. I do not need to use the whole 44" length, it can be shorter, but it cannot be wider than 20". Is this possible?
I am looking at Kato Unitrack 20-170 & 20-171. Kato claims it has the smallest radius available in their tracks. It is an 8" radius.
Could I use these tracks for the circle part of my figure 8?
If so, how many would I need to make this circle fit in a 20" wide space?
How many straight tracks would I need to complete the figure 8?
The 20-320 crossing would have to be used.
I know I can only run a short locomotive on this track, but that is what I will be running on it.
Answer From Forum
If the sections work out like they do in HO, 6 will create a half-circle (180º). If my figuring is right... you should need like 8 or 9 sections per side to make the round parts for the figure-8.
Question
Now when you say 8 or 9 would make a circle are you talking about using the 20-170 or the 20-171 tracks?
20-171 is the short version of the 8" radius tracks
20-170 is the long version of the 8" radius tracks, which I believe to equal 3 of the 20-171 track. Right?
Answer
yes, I mean the full section tracks, not the 1/3 section tracks.
The diameter of the circle would have to be 18" in order for the circle to be at least 20" wide. This will decide exactly how many tracks you will need to make the circle part of the figure 8.
Question
Okay I have the circle. Now how many straight tracks will I need? Which size do I buy? I really need to know the number of the track to buy.
ie; Kato 20-100