Turnout "length"

Dave-

Turnouts are numbered to express the length of the diverging leg of the turnout, in units, necessary to diverge from the straight leg of the turnout by one unit.  Therefore, a number 5 turnout will need 10 inches to diverge to a track on 2 inch centers, whereas a number 6 switch will consume 12 inches of length to do the same thing. 

Jeff Fry

Thanks

Ah!  Such simple math!  I have read several track planning and yard design books/articles and never realized that!

Thanks very much!

Dave

Yard design

One of the key drivers of your yard design will be what size trains you want to put in the yard. 

Traditionally a class yard is pyramid shaped with some tracks shorter than others.  If you want to use the yard primarily as a staging yard you may want to make the yard more of a parrallelogram with all the tracks the same length.

In that case the main enters the yard near the back of the yard on one end and exits the yard near the front on the other end with the leads parallel on both ends.  The maximum length of the yard tracks will be the number of tracks plus 1 x the length of a switch subtracted from the length of the space available.  Assume #6 switches, 12 in long, 8 yard tracks and a 212" long area. 12in x (8+1) = 108", 212-108 = 104"  or 8 ft 9".

Alternatively if length variance isn't aproblem you can save space making the yard diamond shaped, that is the main line enters the yard on each end near the center of the bench and you have a left hand and a right hand lead.  The maximum length of a yard track will be about the length of the space minus 4 X the length of a switch.  The minimum length of a track will be the number of tracks on that side of the main plus 1 X 2 X the length of a switch subtracted from the length of the space available.  Assume #6 switches, 12 in long, 4 yard tracks on one side of the main and a 212" long area.  The shortest track will be 12in x (4+1) X 2 = 120", 212-120 = 92"  or 7 ft 9 in, the longest track will be 4X 12 = 48", 212-48 = 164" = 13 ft 9 in.  So you will have tracks 13-9 and then 2 each of tracks decreasing by a foot each to 7-9.

If you add compound ladders you can almost cut your effective switch length to about 2/3 of a straight ladder, so a #6 switch ladder effectively has a footprint similar to a #4 ladder.  Switches now are effectively 8 or 9 " long instead of 12" long.  Do the above calculations with an 8' switch instead of a 12" switch and you gain several feet in each track.

Turnout length varies by brand

Attractively simple, but sadly not generally correct. The number of the turnout refers only to the frog. What happens beyond the frog varies from brand to brand and even within different lines within a brand. (For example PECO Code 75 vs. Code 83)

Different manufacturers also use different "lead" lengths and different lengths before the points. So this general rule of thumb is not very accurate for precise planning.

Nope.

Switch dimensions

If he is surveying track centers to actually build the layout or cut roadbed where he has to be accurate to a tenth of an inch, you are correct.

If he's noodling on the back of an envelope to get an idea of what he can fit in his footprint and only has to be accurate to within a inch or two, then the general rule of thumb is fine.

Thanks again

Yessir..for now noodling is a more accurate descriptor of my inaccuracy..thanks again all of you.

Reconsider your yard duties

At this point you are planning to use your yard as a parking lot next to an engine terminal. If you design the yard that way you will likely only be able to use it in that manner. If on the other hand you look at it as a tool for classifying trains and building new ones you may find that it is more useful as your interests change. In the short term you can still use it as a parking lot but in the long term it will be able to do much more for you.

As to your questions of length there are several ways to increase capacity of your yard tracks for a given length. A split ladder cuts the length of the ladder nearly in half putting eight tracks in the ladder length of 5. A compound split ladder does even more in some instances. Useing a curved section so that the number 6 ladder is on a number 4 angle will also shorten the length of the ladder and increase the length of the body tracks as well.

There are numerous books on the subject some of which are out of print but many are still available. A great many tips can be gathered from Byron Henderson's blogs and his website. By the way he also does design work for a fee as I understand and could probably put something together for you that would be better than you could do for yourself. Do not take this as an attack just a comment that there are lots of options out there and sometimes the cost of employing someone to do something is cheaper than the cost of your time and frustration and allows you to begin building your layout sooner.

Now if you have your space available and want to try some of these things in a real size format photocopy some of your turnouts with your printer scanner and begin putting them together in various combinations in your space and see what fits. Nice thing about this meathod the learning curve is very short.