Turnouts

[jowalmer]

Layout consists, for the most part, of an outer and inner oval.  I use regular bachmann turnouts (44130 and 131 [DCC]) and 18"R curves (44501).  From the straight on the outer oval I use these turnouts to turn to the inside which makes a siding.  From the siding, I use another set of turnouts to create the inner oval.  One train running on the inner and one on the outer.

I was checking out the #6 turnouts today at the LHS, and notice that 1) the quality of the moving parts are better (no rivets and the pick rail??? has a much better taper, less derailments???) and 2) the geometry of the turnout is different-than the turnouts I am using.  I also notice that there is a small piece of track that comes with the #6.

Question, if I substitute a set of turnouts I am currently using with #6 turnouts, will I have any problems with the siding on the inside connecting together to the outer oval due to the different geometry of the #6 turnouts?  What is that small track section for? 

Would there be problems creating an inner oval using crossovers instead of the inner siding to inner oval?

Too many questions?  No, then good, I have one or two more.  After reading a post on here I learned of the Atlas layout software, downloaded it and have been fiddling.  Is there a library of track in the software from Atlas track that matches bachmann's track dimensions?  For example, with the code 100 library loaded, are the 18"R curves the same dimensions in degrees as Bachmann's.  Are the Atlas #6 turnouts the same as bachmann's?

terminology above may not be correct...I am new at this.  Maybe I should have posted this in the HO threads...oops.  Thanks.

Jim

[Jim Banner]

Turnouts do indeed come with different geometries.  The simplest for planing a layout is the arc-and-tangent type (Atlas calls them Snap Switches.)  These have a constant radius, typically 18", all through the diverging route and can exactly replace 2/3 of a standard 18" radius curve plus 1-1/2" straight.  They usually come with a 1/3 curve so that the turnout replaces exactly a full length of 18" radius curve plus 1-1/2" of straight.  This extra piece can be seen on some of the E-Z Switches.

Then there is the similar but not identical #4 turnout which has an eased curve and is straight through the frog and beyond.  (The arc-and-tangent turnout goes from straight to 18" radius with no transition.)  Many so called #4 turnouts are distorted to make them replace a Snap Switch and the frog is then not exactly a #4.

Number 6 turnouts cannot be arranged to directly replace standard 18" radius track so they are generally made much more like the prototype.  The result is fewer derailments, especially when backing a train through them.  They do take up more room, which means many people avoid using them in switching yards, but if you have the room, a yard with #6 turnouts is a pleasure to operate.

To answer your questions:
The differences in length and in frog angle between regular turnouts and the #6 turnouts may cause you problems.  To get the same distance between parallel tracks with #6 turnouts, you need more length and this added length may not exactly line up with joints in the present tracks.  I believe the short pieces that come with the turnouts may help here.
The biggest problem of using crossovers to create an inner oval would be the loss of the siding between the ovals (if I understand correctly.)

Much of the Atlas planning software will work with Bachmann track as well.  Curves of 18" radius mostly come in 30^o sections with fitters of 10^o and 20^o also available.  Straights come in 9" lengths and often in 27" lengths as well.  The Snap Switches or their equivalent can replace a standard 9" straight on the tangent (straight through) route and an 18" 30^o curve plus a 1-1/2" straight on the divergent route.  Numbered turnouts may differ (perhaps someone else can confirm or refute this.)

One last answer to an implied question - the movable rails in a turnout are the point rails.  If they do not close properly against the nearby stock rails, then wheels will "pick the points" and a derailment will likely occur. 

[jowalmer]

Thanks Jim.

As for direct replacement of the #6 for regular turnouts, I am able to make whatever changes that are needed to accomodate extra length or width in the layout, i just wasn't sure if Bachmann sold the correct straight/curve piece lengths to accomodate the change in geometry.  In other words, because the #6 is a 9.?? degree angle turnout, will there be an appropriate curve to bring the turnout to 90 degrees of the main line without haveing to cut track?  The same goes for when connecting the siding to the main line, will there be straight pieces of appropriate size to make it all work.

Thanks again.

Jim

[Joe Satnik]

I have seen the #6 turnout's departure angle called out at 10 degrees.  (rrtrack.com) 

This may be an approximation, or real, as the we can only guess that the divergent path follows straight off the frog, or guess that the frog was precisely made to 9.5 degrees. 

Calling it 10 degrees does make the math a little easier.

If you are trying to get to 90 degrees, you have 80 degrees left to make up with curves. 

90 - 10 = 80 degrees.

So the trick is to come up with a hodge-podge of curves that add up to 80 degrees, and are within your allowable range of radii. 

The length of your locos and cars will determine the minimum radius.  The max width of your layout will determine the upper radius. 

In the NMRA tables

http://www.nmra.org/standards/sandrp/rp12_3.html

Line 11 shows the RCR or "radius of the closure rail" which is 43" for a #6 turnout.

This is the shortest radius turn that locos or cars will see traveling through the turnout on its divergent route.

When using turnouts, it is good to match your layout's minimum radius to the RCR. 

If the RCR is too small, it becomes your layout's minimum radius.

If the RCR is too large, the turnouts longer length wastes valuable real estate.

If I were to err, it would be to the long side (higher turnout number), thinking of future expansion or re-use, or future longer wheelbase locos/cars.   

If you wanted pure 18"R, 10+10+30+30 = 80 degrees. (Terrible mismatch for #6 RCR.)

22" radius comes in 22.5 and 11.25 degree sections.

26, 28, 33.25 and 35.5" radii come in 18 degree sections. 

33.25"R also comes in 6 degree and 12 degree sections. 
         
If you want 33"+ radii, they are in multiples of 6 degrees.

6 x 13 = 78 degrees, an error of 2 degrees from (target) 80. 

6 x 14 = 84 degrees.

Things improve only a little by adding 22"R into the equation.  (Multiples of 11.25 degrees.)

7 x 11.25 = 78.75 degrees, and error of 1.25 degrees.

Best mix I could come up with, mostly 22"R:

One section 33.25"R / 12 degrees + Three sections 22"R / 22.5 degrees =

12 + 67.5 = 79.5 degrees, or 0.5 degree of error from 80 degrees.

Of course, that takes your min radius down to 22"R.  Phooey.

What we really need is a longer radius 10 degree curve section, say between 33.25"R and the next step above the RCR (43"R). 

Imitating Kato spacing = 2-3/8" increments: 35-1/2", 37-7/8", 40-1/4", 42-5/8" and 45"R.

Continuation of Bachmann 2-1/4" increments: 35-1/2", 37-3/4", 40", 42-1/4" and 44-1/2"R.

NMRA standards Class 1a (largest locos and cars)

2-1/2" up to 40 inch, 2-3/8" above:  35-1/2", 38", 40-1/2", 42-7/8", 45-1/4"R

http://www.nmra.org/standards/sandrp/s-8.html  Scroll down to HO

Here is a possible cottage industry until Bachmann makes a high radius 10 degree curve (needed to bring the #6 turnout back to parallel):

Cut 8 degrees out of the middle of high radius 18 degree curves and sell them as a 10 degree curves for the #6 turnout.

You can wake up now.

Sincerely,

Joe Satnik

Edit: added next larger radius curve (x3).     



       

[jowalmer]

Thanks Joe.  I had to re-read it a few times but I think I get it.