Turnout Radius

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new guy

Active Member
The "new" new, NEW plan calls for a turnout at the very start or along a curve and I'm wondering do the turnout radii match existing sectional track in HO scale. This will make or break the part of the plan involving a turnout at the beginning or along the curve in question. No "horsing" it back into radius, margins are TIGHT right there and it must be smooth.

I know 4's are "tighter" than 6's but just what is the radius on turnouts? Thank You for any info.
 

trailrider

Well-Known Member
Some turnouts, like Atlas Snap turnouts have the diverging track roughly conforming to 18" radius, with the main straight. OTOH, Atlas Custom turnouts have a more straight divergent track which don't fit a particular radius. Both Atlas Snap Switches and Custom Mark IV have the straight route that fits in a standard 9" section. They also have provision for mounting switch machines.
Peco makes turnouts with a double curvature. One I measured on my layout has the outer curve at a 22" radius and the inner curve at 18" radius. Peco turnouts take up more length than snap track sections. Peco turnouts have a snap-over spring on their throwbars which permit either manual operation or using a switch machine, which Peco sells. Personally, I use more positive switch machines, and remove the snapover springs. Peco turnouts come in Insulfrog (with the frog insulated from the closure rails) or Electrofrog, which have "hot" frogs. I prefer the latter, but it depends on your layout.
Shinohara (sold by Walthers) also makes double curve turnouts. The ones I measured, are called #6's, and, like the Peco, measure 22" and 18" on the outer and inner curves respectively. Shinohara turnouts require either a manual ground throw or a switch machine that applies positive pressure to the points. Shinohara turnouts are all live frog.
All turnouts need to have power fed from the point end, and if you have a reversing loop or crossover, the frog ends need to have insulated rail joiners installed to prevent shorts.
Hope this helps.
 
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Iron Horseman

Well-Known Member
I know 4's are "tighter" than 6's but just what is the radius on turnouts? Thank You for any info.
Technically no, North American turnouts do not have a "radius". The absolute correct way to do it is to start the radius after the end of the point rails. As such, the sectional track curves in HO scale do not match a turnout.

However, the HO scale track manufacturer's have jimmied up a turnout that is supposed to fit into an 18" radius curve. In the Atlas world this is called a "Snap Switch". It is approximately a #3.4 turnout. Theoretically one can put a 1/3 section 18" radius curve piece onto it and substitute it for a full 18" radius curve. I've not had much luck doing this. It still always seems a bit larger than it should be.

Also in the Atlas world their Custom Line #4 turnouts (which are really closer to a true #4.5 turnout) are really close to being a 22" radius equivalent. I believe that one has to add a 22" radius 1/2 section to the diverging leg to make it fit. The track in question is code 100 track, one has to cut the 1/2 section themselves.

Likewise if we are talking code 100 track, then we go to the Peco brand. All of their turnouts have #6 frogs, but the are built to a European Prototype that has curved departing rails. Somewhere there is a table that shows what the radius are. I believe a Peco "short" turnout is close to a 24" radius. That might be able to be worked into a curve. Once again a piece of sectional track would have to be cut down to make up the distance. There is also the really small Peco ST-240 and ST-241 turnouts with a true curve of 17.25".

Finally, one gets into all the true curved turnouts. If the track plan allows it, that could be the best solution. Atlas used to make an 18"/22" curved turnout. They can still be found at swap meets and the like. Peco makes one they call the double curve (ST-224 and ST-225) where the inside radius is about 17 3/4".
 
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Selector

Well-Known Member
Be careful of the Walthers/Shinohara line of curved turnouts. I found out the hard way, unless they have since been modified, that their two radii are not as advertised. The two with which I have experience, now ten years ago, were their curved #7.5 and their #8. Neither turnout was usable once I had them in my hand and learned that I was misled. I had to cut all the webbing under the rails so that I could widen the two routes sufficiently that they would work.

The 7.5 was advertised as 28"/24", but the inner route was closer to 21". The #8 was supposed to be 32/28, but the inner was closer to 25". This ended up discussed on the modelrailroader forum, and others learned that theirs, too, were as I had found. Now, all of us who were affected dutifully announce our experience whenever the topic of curved HO turnouts comes up from someone interested in acquiring them.

Only curved turnouts, or the Peco Code 100 English variety (non-Streamline), have truly curved routes through the frogs. N. American style, Atlas and Streamline Electro and Insulfrog Pecos, and the Micro Engineering, as examples, have a straight route through the frog and beyond, even if the closure rails and points rails are curved. Otherwise, if you have to use N. American style, you must concern yourself with the 'substitution radius', details of which you can find on the NMRA site.

It seems to me that Peco must make set track elements that would conform to their curved turnouts, but otherwise, you'll have to get close. If you are within 2" of radius between your flex/set track curves and a curved turnout, it won't make much difference either visually or practically as you connect them. With variances greater than about 3", it will be noticeable and you'll notice a slight jerk in yaw as the rolling stock moves across the joint. Maybe. Viewed from the side, eyes low to the surface, no.
 

montanan

Whiskey Merchant
At one time Shinohara produced curved turnouts. They were at a particular radius to and particular radius. Don't know if they are still available.
 

new guy

Active Member
WOW! Thank Y'all for the most excellent response! Problem solved, Raise up the curved lines and run that diverging line as a completely separate line and run it under the curved lines, no turnout, no worries, well the usual worries anyhoo. Trying to do that particular spot in that particular manner will have to wait till I start hand laying scratch built ties and rails in HO....could be a while on that so raise em up it is! They are "thru lines" and a turnout there was only for access to the area behind the curve to a "parking/storage yard for stock and loco's. Just have to lay more track. (hehehehehe, sweet!)

Thanks again and have a VERY CHRISTMAS!
 

otiscnj

Well-Known Member
Peco also makes a large 'double radius' turnout, which is supposed to be something like 30" and 60". They take a lot of room, but are great for long passenger cars. I've incorporated them into my layouts for years, but my layouts have been pretty large, for a while now.
 

beiland

Well-Known Member
Peco also makes a large 'double radius' turnout, which is supposed to be something like 30" and 60". They take a lot of room, but are great for long passenger cars. I've incorporated them into my layouts for years, but my layouts have been pretty large, for a while now.
Yes, I've discovered I have quite a few of these in a collection I purchased,...and likely will not be able to make use of them on my relatively small layout plan. :(
 

Selector

Well-Known Member
Yes, I've discovered I have quite a few of these in a collection I purchased,...and likely will not be able to make use of them on my relatively small layout plan. :(
If you ever have the occasion to consider boring through the drywall and onto a shallow shelf on brackets bolted to the drywall and studs on the other side of the same wall, you can make two or three tracks to store ready-made trains. When space is tight, and you'd rather not have to package up cars or locomotives to run another type of train every other week (this is when your collection of rolling stock and motive power grows a bit), you can store complete trains on a 6-10' shelf. The access to that storage would be via the outer route on the wide Peco curved turnout. So, if you could ever see this happening (you can always patch a hole in drywall, sand, and cover with paint), now might be the time to insert this turnout into a curve where the trains would use the inner route 95% of the time. It's a thought. You'd be surprised how many modelers have had a eureka moment and made a tunnel portal through the closest wall and have tracks running onto some sort of staging or storage to save themselves some trouble.
 




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