Planning stage of layout: Specs for no "S" curve?

Hi Matt,

Which track/switches are you using?

It's 2 of the same switch for a crossover. Using curves from the divergent track to bring it back to parallel (to another thru on a switch) depends on the engines you will use and which center rail spacing that you desire. Placing a short straight in there will permit higher speed switching and increase the track spacing.

The engines have a minimum diameter curve that limit what you use. 

Two O72 LH or RH directly connected is fine for most engines for a crossover. Coming back to parallel using O72 curves from an O72 switch is usually ok for most engines. These just aren't high speed switches like a #5 for example.

The S can get you on the mainline with two opposite curves connected directly causing problems with larger cars, steamer cabs and scale couplers that are closer together. Again, this happens more with curve diameters smaller than O72.

Now, your constraints - building near the furnace will be a problem with furnace maintenance. If you insist on building near it anyway, then it is simply a matter of clearance for the overhang of cars. 

I would check the equipment that you will using for the cars/engines with the greatest overhang to find the minimum using the curves for that area. This, too, is usually a problem with less than O72 diameter curves. 

3 inches is plenty in most cases. You must actually determine the minimum for the equipment is a tighter fit is required.

Your minimum distance to avoid a S curve is equal to the longest piece of Rolling Stock you plan to use.

Since you are using O-72 curves, I assume your couplers are truck mounted and not body mounted.  Body mounted couplers usually need broader curves.

With truck mounted couplers, as Carl stated O-72 S curves normally are not a problem.  Aesthetics is another issue.

With body mounted couplers, and especially with Kadee type couplers, you need to follow John's advice.

Thanks for the insight! 

Regarding the curves and rolling stock. I'm using gargraves wooden tie track. My main line has the O72 curves where the S configuration comes into play. The inner loop currently is O54. I'm planning on using Ross switches (this configuration seemed to be the most recommended). I am attempting to keep a 3 foot buffer between the layout and utilities.

In terms of rolling stock, just the standard cars from Lionel, MTH, etc.

I'll post a picture later today when I'm back on my computer.

One question regarding benchwork. OSB or plywood for the top?

I intentionally built-in a S Curve on the 12x15 club layout. The S Curve is on the right side of the layout.

It was done to:

• Strongly discourage use of scale rolling stock. We wanted this as a Traditional only layout.
• Prevent "the kids" from attempting Mach 1 speed when running conventional

Traditional rolling stock operated at moderate speed runs through this section fine.

The Polar Express snaking through this section actually looked pretty nice.

For a new module that I am designing, I avoided the S Curve by ensuring there is > 20" between the frogs...

Here's the current iteration:

The top is the wall of the basement, with a support block sticking out (shaded in gray).

Approximately in the center, there's a 5" support column (also shaded in gray).

The furnace/hot water is also in gray.

Orange indicates the clearance that I would "like" to have (4' from left wall, 3' from right wall, 3' in front of furnace).

Thoughts, ideas, criticism? 

Matt the only S-curve I see is on the lower right side of your plan.  I would start further to the left and use a standard O72 left-hand switch here, with the curved leg going directly into tangent track (or an easement made with flex track.)

What I always heard, is that you should insert a straight section in the middle of the S-curve equal to the longest rigid wheelbase of your locos.  So for a scale Berkshire, etc., you would need about 4 inches to prevent the first and fourth axle from simultaneously going in different directions.  If you'll be running Texas types, etc., maybe 5".  Most "traditional" locos, small diesels and 4-wheeled steam won't have a problem.

There are a lot of ways to achieve a crossover between mainlines without creating an S-curve.  Some of the track systems come with removable pieces so you can butt the diverging leg of the turnouts directly against each other.  As someone else mentioned you could use #4 or #5 turnouts if they are available for your track system.  These have a straight diverging leg instead of a curve. 

If you're making a crossover with Ross O42 or O54 switches, you could even cut part of the curved legs off to avoid "over steering."  In other words, if the stock diverging curve is 32 degrees, cut it back to 22.5 degrees and do the same with the receiving switch.  This will eliminate the S curve.  You might have to insert a short, straight cut section between the switches to maintain the spacing of your mainlines.  Good luck!

Ah, I didn't even see that one, thanks! 

I'll post an updated plan later today. 

I don't see anything that would be a big problem.  If you already have the curved turnout, slide it down to the left one piece and the diverging line will flow directly into that route.  It looks like your upper level will work fine.  I would be more concerned with access to the four turnouts along the back wall.  Can you reach them, will they be covered with scenery?

The four turnout near the back wall will be accessible, as the layout will only extend a few inches past the outer track. I don't know how to model that, though :-/

Here's an updated look: (I'll have to do some fancy benchwork to have access to the O54 tunnel from underneath if something goes astray...)

And here's the area I have concerns about:

Currently, there's ~12" straight between the two diverging curves. Is this enough? Should I add more (somehow)? Can I reduce or remove this all together to get more clearance by the furnace? (Oh the joys of constrained space...).

Thanks for all your great input so far!

Matt_Goodman posted:

The four turnout near the back wall will be accessible, as the layout will only extend a few inches past the outer track. I don't know how to model that, though :-/

Here's an updated look: (I'll have to do some fancy benchwork to have access to the O54 tunnel from underneath if something goes astray...)

 

 

 

Currently, there's ~12" straight between the two diverging curves. Is this enough? Should I add more (somehow)? Can I reduce or remove this all together to get more clearance by the furnace? (Oh the joys of constrained space...).

Thanks for all your great input so far!

Here's how you can handle access - check out the 3/18/11 post of the Hidden Pass Junction layout build for a clever access hatch - aka fancy benchwork

The only way to get more clearance near the heater is to move the entire section toward the pillar clearance space. I don't see a problem eliminating the 12" straight at the area of concern. 

if you feel that you must keep that in there, then, the whole layout has to move toward the pillar.

I don't think you will have issues.

The S turn issue varies by scale, equipment, and operations.

  The backing issues have been covered, it's about pushing geometries; angles from truck to truck. The shorter the better.

  When two "talgo trucks" are on opposing curves, the couplers don't always point at each other enough, and some coupler binding occurs sometimes. Other times one truck is twisted off it's rails.

 Longer distances from a trucks pivot to coupler only compounds the offset in curves with couplers having greater overhang off center rail.

  On 0-27 you only need about a 4" section between opposing turns with truck mounted couplers to avoid this.

  Your minum goal would be one car's truck in a curve, the next car's truck on the straight.  So I'd say you are covered unless you lean towards long stock.

The rule of thumb for S curves I was given by other oldtimers such as John Armstrong, was to allow a straight section equal to the longest car between the opposing curves if at all possible.

Armstrong was working in 2-rail, where most of the cars have body-mounted couplers.  In 3-rail O, the limitation is most often the rigid wheelbase of a steam loco.  Unlike 2-rail scale models, most of our steam locos have one-piece side rods that directly connect the first and last axles.  Some lateral play is built in, but if the first axle is in a left turn and the last axle is coming out of a right turn, there will be a huge increase in friction, if not a derailment.

12" is more than enough.  Unless you're planning to run a 2-10-4 Texas or the UP 4-12-2, four inches is probably enough for reliable operation.  If you're worried about how things LOOK, or the overhang on articulated locos, well that's a different set of considerations.