Basic 2 Rail Atlas O Oval

I believe 16 (curved) pieces will give you your basic circle. I would go ahead and get a few additional curves, cause you never know...🙂 It's pretty nice stuff...

Mark in Oregon

Hoping to be able to run max size of SD40 and 4-8-4 steam on a 40.5 R. Not sure if I can operate any passenger cars on that radius?

@Classy Woods, LLC posted:

Hoping to be able to run max size of SD40 and 4-8-4 steam on a 40.5 R. Not sure if I can operate any passenger cars on that radius?

The SD will probably be okay; if your Northern is full on 1/48 (and since we're talking 2 rail, it probably is) then I would be surprised if it does. That's a pretty long rigid wheel base.

Passenger cars (80' ?) perhaps. Shorter ones should be fine.

Let us know how you get on... with photos, of course! 🙂

Mark in Oregon

with your Northern and full length passenger equipment. you may be more satisfied if you went to the next size radii curve. if you have the room.

40½" is a bit tight.

As a general recommendation consider matching equipment and curve radii to the area you have available for a layout to be built.

If 40.5" radius is what your space will allow think about smaller locomotives and shorter cars.  That will provide a much more enjoyable running experience.

We set up a multi radius test track at an earlier 0 scale national event with eight different "S" curve radii running from 49 1/2", 54", 60", 64", 67 1/2", 72",  &  76 5/16".

Most 4-8-4 locomotives were climbing the rails at 54" radius.  You can tinker with the chassis for smaller curves but that is the exception.

<<< Non show use

an 81"  Diameter Or 40.5"r , should let you run a 4-6-2 ( and smaller) and most diesels , Correct?

@Dave Koehler posted:

an 81"  Diameter Or 40.5"r , should let you run a 4-6-2 ( and smaller) and most diesels , Correct?

I would think so.  FWIW, my All Nation 4-6-0 and diesels (all B-B types) track fine on 36"R, so with 40.5" you will probably be fine. 👍

Mark in Oregon

I would say if you are using an Atlas or MTH 2 rail SDxx you should be OK on 40.5"  Atlas specifies 40.5" for their SD40 but I've seen claims that they will also negotiate 36" radius.  I suspect that 3rd Rail (Sunset) or brass SDs (Overland, US Hobbies, etc) might have problems on 40.5" most are specified at 48" radius.  With regards to the 4-8-4 it probably needs a much larger radius depending on the manufacturer.  Even MTH specified 54" for its 2 rail NYC Mohawk.  Sunset builds most of their larger steam to negotiate 56" radius and I've seen some Key imports and Overland X-8-X locos require 60+".

A word about Atlas and MTH - Manufacturers tend to rate the minimum radius for their engines based on the minimum radius of their track so you may find that they *MIGHT* negotiate slightly smaller curves.  Atlas SW9s are rated for 24" Radius but as an experiment I discovered mine will run on 17" but not with anything longer than a 34' car attached.  Of course anything but "lift-and-separate" uncoupling (with real Kadees) would be the order of the day on that tight a curve.

My Northerns have trouble below 70" radius.  Biggest problem is lead/trailing truck hitting stuff.  MTH cures that with undersize cylinders and missing tail beams.  I would rather leave a Northern on the shelf than do that to it.

@Jim Scorse posted:

I would say if you are using an Atlas or MTH 2 rail SDxx you should be OK on 40.5"  Atlas specifies 40.5" for their SD40 but I've seen claims that they will also negotiate 36" radius.  I suspect that 3rd Rail (Sunset) or brass SDs (Overland, US Hobbies, etc) might have problems on 40.5" most are specified at 48" radius.  With regards to the 4-8-4 it probably needs a much larger radius depending on the manufacturer.  Even MTH specified 54" for its 2 rail NYC Mohawk.  Sunset builds most of their larger steam to negotiate 56" radius and I've seen some Key imports and Overland X-8-X locos require 60+".

A word about Atlas and MTH - Manufacturers tend to rate the minimum radius for their engines based on the minimum radius of their track so you may find that they *MIGHT* negotiate slightly smaller curves.  Atlas SW9s are rated for 24" Radius but as an experiment I discovered mine will run on 17" but not with anything longer than a 34' car attached.  Of course anything but "lift-and-separate" uncoupling (with real Kadees) would be the order of the day on that tight a curve.

This is no doubt the case.

I initially had some of the older Roco made Atlas track, which is 24"R. I found that I could run my diesels and 40' cars on those sharp curves if I mounted the KDs with only the back screw, and didn't tighten that screw all the way, to allow some lateral "play".

It looked ridiculous, but it did work. As always, the largest radius you can get away with, the better. 🙂

Mark in Oregon

At this time all I have is a Sunset/3rd rail GP7.  An absolutely beautiful locomotive I can't wait to run it.   I'll have to rethink things as it seems steam commands larger curves.  When I do this, I'll provide videos and results.   My longest piece of rolling stock is a 60' boxcar.  I guess once I lay track and try it out, I'll find out what works and what does not work.  Someday I may have a larger area but at this time I am happy to at least start a layout.

Thank you for the replies.

@Classy Woods, LLC posted:

At this time all I have is a Sunset/3rd rail GP7.

3rd rail GP7/9 locos have a 48" minimum radius although they might go around 44.5".  60 foot cars should be no problem at all on 48" and probably OK on 44"

@Jim Scorse posted:

3rd rail GP7/9 locos have a 48" minimum radius although they might go around 44.5".  60 foot cars should be no problem at all on 48" and probably OK on 44"

I ran one around a 36" radius and it runs fine, which makes sense considering its the same mechanism as the 3 rail one with a different set of wheels. I suspect you may even be able to go tighter than that so long as switches arent that tight.

MTH is a little more hit or miss with their ratings but you'd be surprised what they can do if you're ok with it looking a little clowny. Even the ES44s will clear a 36" radius without problems. The only diesel that has been an issue is the SD45T-2, but the issue isnt the tracking, its the squared off rear porch interfering with certain cars placed behind it.

4 axle MTH and atlas stuff, I'd say you're good. Even the trainman C40-8Ws are 36" radius rated on the box.

I would like to make the following suggestion IF your space permits it:

Instead of buying 16 sections of the 40.5", buy 8 sections, and buy 4 of the 45"and 4 of the 49.5".  Arrange each end so that going from a straight section you have a 1 @ 49.5, 1 @ 45, 4@ 40.5, 1 @45, 1 @ 49.5.  Doing this will give you a more gentle curve at the beginning of each curved portion, which may make it easier for some equipment to traverse the sharper 40.5 portion.   This will also give you enough sections to form a 90 deg curve w/ straights at each end as three test tracks to see what does and doesn't work on the different radii.

If you bought just half of the sectional track [ = one "end" ] you could also use those sections to use as a guide to make the other end from flexible track -- that Atlas sectional at current list prices is rather expensive.

Have fun !

SZ

Edited to add:  I note your location;  you might consider first attending the "March Meet" a month from 'now' before purchasing the track if you were not already planning on it.  There typically have been good bargains on track at the recent 2R meets I've attended and I think the RT gas / tolls would be worth it financially, plus you could get a lot of questions quickly answered by people who know what they're talking about.