Turnout numbers and curve radius

[GerFust]

Is there a source someone can point me to in order to understand into what radius curve a #4, #6, #8 turnout takes the layout? If working with 22 inch radius track, what number turnout should I use? If placing a turnout on a curve, how do I know what the smaller and larger radii are when buying a turnout?

[edo1039]

I would suggest the larger #'s and the 4's for yards or branchlines.i am sure you will get a lot of hits on this.

[Anonymous]

Hi, Gerald, I go along with Ed on this one #6 or larger on the mainlines and #4 in yards or branchlines. As far as turnouts having radi that match various curves I don't think there are any exact matches. The Atlas "Snap Switch" is an 18" radius curve to match their sectional track but as far as I know that's it. Use flex track to build your layout that way you don't have to limit yourself to any fixed radi and you can transition your track to fit smoothly to your turnouts on their diverging side. Unless you use a curved turnout a turnout in a curve is not a good idea. Check out the Shinahora and Peco and Model Engineering line of turnouts all are execellent...Hope this helped...Vic

[Anonymous]

There is an "equivalent radius" for the switches - see John Armstrong's "Track Planning for Protptype Operation" for details. But you need to know that, with a few exceptions, the diverging leg of a turnout has both curved and straight sections in it, rather than being one continuous curve. Therefore the diverging leg should not normally be used in as part of a curve. It maybe OK at the start or end of a curve, but not in the center of a curve.

[Anonymous]

I agree that you should read John Armstrong's book. Assuming you are in HO Scale, remember that the Atlas #4 Customline series turnout is actually a number 4-and-a-half frog. If you join the NMRA you will receive their standard dimensions of a variety of turnouts which should be fine for planning purposes.

Yes, the 'curved' leg of the turnout is actually made of a curved portion and a straight (tangent) portion. My recollection is that an Atlas #4(1/2) turnout has a radius of closure rail equal to 22 inches, but after considering the tangent portion, the 'substitution radius' is 36 inches. So an Atlas #4(1/2) is comparable to a 22 inch radius curve, although I encourage you to use #6s if it doesn't cause you any undue sacrifices. Incidently, turnouts often make good transition curves when placed properly at the beginning (or end) of a curve. I believe the substitution radius for the Atlas #6 is 60 inches and the radius of the closure rail is something tighter than that.

Good Luck - The Other Ed

[Anonymous]

I "inherited" 1/2 of a layout, had to make the 2nd half to make a whole layout. The "legacy" portion has a turnout in the middle of a curve, which I kept (but relaid the track to a smoother radius.) So, what is bad about a turnout in the middle of a curve? This is an Atlas 4 (1/2) on a 20" radius curve. I can't really take it out, but is this a "non-prototypical" issue or a "I'm surprized you don't have trouble" issue?
Dean

[Anonymous]

It's a little of both. Using the diverging leg as part of a curve puts a "kink" in the curve. This can cause problems, not always, depending on the quality of the track-laying and rolling stock, the speed involved, etc., etc. Just like so many other things in this hobby, what works for one is taboo for another. If you aren't having problems, don't worry about it, and if you are, you know where to look!

[GerFust]

Thank you all, that was helpful. I'm planning on building a small space layout very loosely based on the St. Paul Central which contains a turnout in mid curve - and yes, I'll use a curved turnout there. Without a turnout in the curve isn't much room for a decent length passing siding in a 4x8 layout. They placed two straight sections in the midst of a curve (including the turnout), which appears to have limited them to 18" radius on one end of the layout. That's something I want to avoid. After two unsuccessful tries at a layout, I'm retreating and starting small and trying to build some skills so that the darn thing actually works.

[Anonymous]

Hi Gerald, I downloaded that track plan and I see the problem that you are trying to avoid. You're limited to 18" curves on the left hand end of the layout. Do you have room to make this layout larger? If you could make the layout say 2-3 ft wider and longer it looks like everything would "drop" into place with 22" curves, or larger, on both ends and a longer passing siding. Sometimes track plans on paper just don't translate well to plywood...HA HA. Don't give up... keep plugging at it. Take Care...Vic

[Anonymous]

Gerald,

I opened the track plan and looked it over. How strong is your attachment to that track plan? It appears to include Atlas snap switches and has several reverse curves. I could adjust a few items and improve the alignment if you care for the assistance. I recently built a 4 x 8 ish layout for my son on a piece of plywood. Let me know if you would like to explore some options with regard to this plan.

Good Luck - Ed

[GerFust]

Ed:

Thank you for the offer. I might take you up on that. I'm not using EZ track (or whatever it's called) - I'll be laying flextrack with normal turnouts and cork roadbed. And the published track plan isn't something I'm sold on. I had designed a 5x10, then scaled it back to 4x8. After that I was surprised to see that published track plan had generally the same elements I wanted.

After all the feedback given above, I'm back to 5x10 (although much different than where I started). I think the benefits are clear, wider radii, ability to NOT run parallel to the layout edge, a broad curve rather than a straight on one edge, longer sidings without curved turnouts (although I may still add one). I'll still keep it flat (hopefully my first completed layout, so no need to get too fancy), use #6 turnouts (and #4 for the yard, since I own them already), *** view block in the center, and have a line off the layout to another section holding the staging tracks. If interested in taking a look at it once I have it on paper (or a download or MS Excel drawing), please email me at [e-mail].

Thank you!

[Anonymous]

I look forward to working with you.

Ed