Turnout Quesiton

[Darick]

I am wondering what the difference is between a number 4 turn out and number 6 or 8.  I am building a layout with 22" turns on the main line. I want to make sure I choose the right turnout.   

Darick

[dehusman]

The number of a turnout is the ratio of the angle at which the tracks diverge.

In other words if a switch has a #6 frog and turnout then for every six units, the two routes diverge one unit  So with a #8 frog for every 8 units of run they diverge 1 unit.

Most N American switches are straight through the frog and the diverging route is straight, with the exception of Snap Track #4 which are 18" radius.  European switches are curved through the diverging route.  So you can't just drop a N American prototype switch down in a curve and expect it to match.

Dave H.

[jrbernier]

Darick,

  There is no HO turnout that has a 22" radius curve through the divirging leg of the turnout.  Most North American protype practice uses 'numbered' turnouts.   The divirging leg moves away at an angle.  #4/5/6/8 turnouts follow this standard.  A #4 moves away from the straight at a ratio of 1 to 4.  A #6 moves away with a ratio of 1 to 6, and so forth.  The Atlas Customline #4 is actually a #4.5 turnout and would be a good match for your 22" radius trackage, but it will not replace a 22" radius piece of sectional trackage.  The Atlas 'Snap  Switch' does have a constant 18" radius through the divirging section of the turnout, and is meant to be used with sectional track.

Jim Bernier

 

[selector]

I know what you are probably asking for.  Will the #6 or # 8 turnout be a better partner for the curves I intend to use, and will my rolling items be able to use them okay?  Dave is right about the ratio of divergence at the frog.  But, because the diverging route only curves until just as it gets to the frog, and then leaves the turnout in a line, it won't work on a curve.  But if you are just wondering what is a good match to make sure you don't get derailments, you can use a #6 turnout for equipment that would begin to struggle on 30" curves no problem.  I don't imagine you have anything that would have to go slowly through a 30" radius curve?  If not (since you tell us it'll be 22"), be secure with a #6.

[Pathfinder]

I would think that No.4 would be alright as well, as I have had good success with them on locomotives and cars that run well on 24" radius.

It will be a tighter turn of the straight track but would also be more in keeping with the radius you have selected for your mainline.  Just have the locomotives and cars in keeping with the mainline, so keep to B-B diesels and smaller steam locomotives (ie 2-6-0, 4-4-0, maybe a small 2-4-4-2/2-6-6-2 logger), 40' freight cars and "shorty" passenger cars and you will do fine.

But if expansion is possible in the future, with bigger curves and bigger equipment, the stay with the No.6 turnouts.

[IRONROOSTER]

Here's the NMRA's table of dimensions for HO turnouts.  Be advised manufacturers don't always follow these.  For curves the two critical domensions are 6 and 11.  6 is the overall curve of the turnout which for a #4, #5, and #6 is 43" and a #8 is 117" - all of these are more than ample for your situation.  11 is the curve of the rail through the turnout which for a #4 is 15", #5 is 26", #6 is 43", and #8 is 67".  This latter radius affects fixed wheel base steam locomotives the most and you should make sure this is your minimum radius or greater.  In this case a #5.  Atlas #4's are really #4 1/2 and should work with 22" radius curves.

John Armstrong's book Track Planning for Realistic Operation explains this and other critical dimensions for model railroads very well.  I consider it to be the one essential book every model railroader should have. 

Enjoy

Paul