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Turnout number.

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Turnout number.
Posted by 1arfarf3 on Tuesday, July 21, 2020 5:00 PM

What HO turnout number to install in 32" radius curve? 

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Posted by peahrens on Tuesday, July 21, 2020 5:35 PM

I'm no expert on this but by looking I can start the conversation.  

1.  If you want a straight turnout, where the diverging route continues the curve, I presume you want a turnout where the curved rail radius within is no tighter than 32".  Looking at NMRA Recommended Practice RP12-31, I see that a #5 turnout has a 23" radius and a #6 has a 35" curved portion (closure rail) radius, so you would choose the latter.  Note that this does not fit your 32" curve precisely due to the mis-match plus the straight sections at each end of the turnout, etc.  Plus, I don't know if the manufacturers' turnouts adhere to the RP exactly anyway.  EDIT:  Reading elsewhere, it is pointed out that only one truck at a time is on the closure rail radius, so the #5 turnout with 23" or so closure rail radius should be fine operationally.

2.  If you are looking for a curved turnout, you can choose one where one curve is nominally 32" and the other outlet track is either tighter or wider radius, if available!  I have some #7-1/2 curved turnouts (nominal 32 / 28 radii).  And if you want the tighter curve to be 32" or more, that would be a high curved turnout, maybe #8 (36 / 32 radii).  I don't see anything by Walthers available now, except fairly tight radii (26 / 24).  I know PECO makes curved turnouts but don't know the details.  And availability also depends on the track code you are using.  You might find what you want on EBay.  If you need a curved turnout, others know more details than I.  

Paul

Modeling HO with a transition era UP bent

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Posted by Pruitt on Tuesday, July 21, 2020 5:41 PM

The best thing to do is google "turnout substitution radius." It will provide a number of links that address your question. One of them, on a forum I don't think we're supposed to link to, says that the #4 substitution radius is 29 inches. The Atlas Custom-Line #4 turnout is actually about a #4 1/2, with a substitution radius of 36".

 

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Posted by BigDaddy on Tuesday, July 21, 2020 5:46 PM

I seem to remember that some of the "advertised radii" are optimistic.  Do I remember incorrectly?

Henry

COB Potomac & Northern

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Posted by peahrens on Tuesday, July 21, 2020 6:04 PM

BigDaddy

I seem to remember that some of the "advertised radii" are optimistic.  Do I remember incorrectly?

That is true of the Walthers-Shinohara 7-1/2 (32 / 28 radii) and similar turnouts of 2012 and earlier.  I believe the small radius turn was advertised about 2" wider radius than actual. 

Paul

Modeling HO with a transition era UP bent

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Posted by riogrande5761 on Wednesday, July 22, 2020 11:15 AM

Rio Grande.  The Action Road  - Focus 1977-1983

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Posted by selector on Wednesday, July 22, 2020 11:21 AM

You're both saying the same thing, different construction.  

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Posted by gregc on Wednesday, July 22, 2020 11:48 AM

Pruitt
The best thing to do is google "turnout substitution radius." It will provide a number of links that address your question. One of them, on a forum I don't think we're supposed to link to, says that the #4 substitution radius is 29 inches. The Atlas Custom-Line #4 turnout is actually about a #4 1/2, with a substitution radius of 36".

how is that "substitution radius" measured?   

  • from the points thru the frog
  • from the points to the end of the diverging rails

and is it the equivalent to a curved piece of track?

 

the following shows possible #6 turnouts contructed with different lead lengths (distance from point to frog).   the angle of the curved section of track (blue) must match the frog angle (of course if can be compound curves.   shortening the leads requires a smaller radius and a section of straight track (red).

 

 

 

NMRA TN-12 specifies a lead length of 6.5" and curved rail radius of 35.4" for a #6 HO Scale straight switch turnout.   i don't understand how the measure/calculated a radius of 35"

greg - Philadelphia & Reading / Reading

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Posted by cuyama on Wednesday, July 22, 2020 3:14 PM

1arfarf3
What HO turnout number to install in 32" radius curve? 

No commercial turnout will fit smoothly and perfectly into a true curve, if that is what you are asking. If that’s not what you are asking, providing more information may help others help you.
Even curved turnouts are slightly off from a perfect circular curve due to the points.

 

Byron

 

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Posted by RR_Mel on Wednesday, July 22, 2020 3:41 PM

Byron

I thought I would post this info from a previous enquire on frogs.  I took a picture off the internet of an actual Peco turnout that I did an overlay on my CAD.  It took a bit of tinkering to work out the dimensions but as the picture shows the rails do come out perfectly to fit the circles on the CAD.



I only ran this Peco turnout.



Mel


 
My Model Railroad  
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I'm beginning to realize that aging is not for wimps.

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Posted by cuyama on Wednesday, July 22, 2020 4:30 PM

If you compare the actual parts (I have) with the equivalent curves, you'll find that there is still a difference from a pure circular curve. There has to be, or I’m pretty sure that the point rails couldn’t work for both paths. 

It's small, but if the original poster is trying to a lay a new turnout into an existing curve, it won't line up. That’s why I asked him/her the question.

 

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Posted by RR_Mel on Wednesday, July 22, 2020 5:34 PM

Byron

I’m far from a draftsman but I have been using CAD programs for 35 years and this particular Peco turnout points look to be super close.



The way I set it up was by importing a Peco Picture from their site then playing with circle dimensions (radius) and moving them (circles) so that the circle overlay matched the rail curvature. 

I took the turnout measurements off the Peco site.  I made the rail width .04”.

The radius dimensions are to the inner rail not the center of the track, although .32435” won’t make much difference in 60”



Mel


 
My Model Railroad  
http://melvineperry.blogspot.com/
 
Bakersfield, California
 
I'm beginning to realize that aging is not for wimps.
 

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Posted by cuyama on Wednesday, July 22, 2020 5:39 PM

Mel, certainly not questioning your drafting skills. But I don't see how lead and point rails that work for both radii can be a pure circular curve for either route, let alone both routes.

When I had this part in front of me on the bench, it seemed easy to see the difference from a circular curve. But it may not matter either way depending on what the OP actually wants to do.

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Posted by selector on Wednesday, July 22, 2020 7:45 PM

To my eye, the top point in the graphic is tangent, or offers a very close approximation of tangent rail, and so I'm going to agree with Byron...no N. American style turnout of any description is going to conform to a true radiused arc across the angle of arc.

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Posted by Anonymous on Wednesday, July 22, 2020 8:32 PM

Having used the Peco turnout, it doesn't exactly substitute for either 60 or 36" radius.

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Posted by Pruitt on Wednesday, July 22, 2020 9:27 PM

gregc
how is that "substitution radius" measured?   
  • from the points thru the frog
  • from the points to the end of the diverging rails

and is it the equivalent to a curved piece of track?

As far as I know, the substitution radius is the equivalent curve radius of the entire turnout, from the beginning of the lead-in at the point end to the end of the lead-out at the diverging leg end. As manufactured, without modification. 

That would mean you can adjust the substitution radius a bit by shortening the lead-out past the frog, and shortening the lead-in towards the points.

Anybody got a different definition? 

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Posted by gregc on Thursday, July 23, 2020 5:49 AM

Pruitt
As far as I know, the substitution radius is the equivalent curve radius of the entire turnout, from the beginning of the lead-in at the point end to the end of the lead-out at the diverging leg end.

as far as I know, the only turnout that is a direct replacement for a curved section of track is the Atlas Snap Switch that replaces a section of 18" radius Atlas curved track.

the Atlas Snap Switch is different from the Atlas #4 Switch which is a conventional switch with straight diverging rails.

greg - Philadelphia & Reading / Reading

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Posted by cuyama on Thursday, July 23, 2020 9:41 AM

Both the 18" radius and the 22" radius Atlas HO Snap-Switches have a short straight section in front of the points (1½", IIRC). So even they don't fit smoothly into a curve.

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Posted by gregc on Thursday, July 23, 2020 11:32 AM

here's an illustration of substitution radius.

the following shows a #6 turnout with 4 different lengths of divergent rails from the frog: 0, 1, 2 and 3".   

of course a length of 0 means the length of the frog is zero and is impractical, but that is where a curve would need to continue from to match the radius of the closure rail

when there is a length a straight tack beyond the frog, the turnout could fit into a curve with the right radius.   the center of the curve would pass thru the midpoint between where the divergent rails end and extend past the points to finally become tangent with the centerline of a straight track if the turnout was extended.

 

 

here's a table listing the substitution radius for various frogs and divergent track lengths (the column for 0.0 is the closure rail radius)

#           0.0    0.5    1.0    1.5    2.0    2.5    3.0 Divergent Length (in)
#     10  132.0  142.0  152.0  162.0  172.0  182.0  192.0
#      9  106.9  115.9  124.9  133.9  142.9  151.9  160.9
#      8   84.5   92.5  100.5  108.5  116.5  124.5  132.5
#      7   64.7   71.7   78.7   85.7   92.7   99.7  106.7
#      6   47.5   53.5   59.5   65.5   71.5   77.5   83.5
#      5   33.0   38.0   43.0   48.0   53.0   58.0   63.0
#      4   21.1   25.1   29.1   33.1   37.1   41.1   45.1

 

greg - Philadelphia & Reading / Reading

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Posted by gregc on Thursday, July 23, 2020 11:33 AM

cuyama
Both the 18" radius and the 22" radius Atlas HO Snap-Switches have a short straight section in front of the points (1½", IIRC). So even they don't fit smoothly into a curve.

certainly not in the middle of a curve, but where the curve starts if a corresponding amount of straight track is also removed

greg - Philadelphia & Reading / Reading

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