I just want to know whats the smallest diaimeter round ho track layout i can make and whts the different 18 or 22'' things mean on curved track? im short on space right now. Thx
The numbers (18", 22" etc) are the radius of the curve measured at the centerline of the track. Most packaged train sets come with 18" radius track, which will form a circle that will fit, barely, inside a square 40 inches on a side. Fifteen inch radius sectional track will need a 32 inch square.
The absolutely smallest round HO 'layout' ever built had a minimum radius of 8,25 mm plus half the diameter of a silver dollar. Slightly larger ones have been built on an old 78 rpm record and the brim of a bowler hat. All showcased either an extremely small four wheel steam locomotive or a four wheel street car, running alone.
In my own work, I have one railroad that runs on 350 mm radius curves, just under 14 inch radius. It is restricted to very short cars and small steam locomotives. Its main line connection runs to 24" radius, because it has to handle long cars and big juice motors with six powered axles. Those long cars and long-wheelbase locos are embargoed from the tight-radius line - they can't take the curves.
Chuck (Modeling Central Japan in September, 1964)