Murphy’s Law - I’m at work without my “MR” booklet with the dimensions for a bazillion turnouts. Apologies if this has been answered, couldn’t find it in a forum search: What is the diverging path radius for an Atlas HO Code 83 #4 Custom Line turnout? Thanks!
Numbered turnouts are NOT a specific radius. An Atlas code 83 #4 custom line is actually a #4-1/2, and has a diverging frog angle of 12.5 degrees. The frog is straight, all the curving happens before it.
A real #4 has a frog angle of 14 degrees
Years ago John Armstrong calulated “substitution radius” for most turnouts, including the Atlas #4, but placing the turnout in this curve will not result in smooth operation. He used this as a guide in matching minimum radius to minimum curves in layout design.
His subsititution radius for the 4-1/2 Atlas turnout is 36".
Sheldon
A numbered frog normally has a radius for the curved portion between the points and the frog called the closure rail radius in the NMRA turnout diagrams. My best guess is that Atlas designed their closure rail radius to be about 22" to match their Snap Track. By the NMRA RP, a #4 has a closure rail radius of 16" and a #5 is 26". The Atlas frog angle measures to a #4.5 so a 22" closure rail radius is a pretty reasonable guess.
Turnout manufacturers seldom follow the NMRA RP in designing their turnouts. Most manufacturer’s #4 turnouts deviate in some way so that the RCR is greater than 16".
Note that the radius of the closure rail (RCR) has nothing to do with the substition radius of the curved path. The substitution radius is a curve for which the diverging path of a turnout can be approximately substituted without re-laying the curve. The substitution radius is much higher than the RCR, and is affected by how much straight track is beyond the frog and points as well as the internal frog to point geometry.
Fred W