Skip to main content

I'm building a RR layout with an overall design of an O-72 loop close to 4 walls with another O-90 circle (with as much straight-run expansion as I can fit) inside that.  The 2 loops will be connected at least twice, using 4 switches I have.  For each loop, these are the widest curves I can reasonably fit.  Of course I can always be unreasonable if I want to be, but only if it guides me to the best decision.

My switches are remote Gargraves rated O-72, and except for 6 short straight Gargraves terminal tracks, the rest is Gargraves 37" flex track.

Also, for purposes of the question below, I'm not interested in side or height clearances in this discussion, because they've been covered already in other topic threads I've read here.  From those discussions I've already determined that my side clearances will always be wider than 3.5" from center rail, and height in tunnel run 6" above rails.  So here I'm only interested in the rating of the turn radius, O-72 being a 36" radius.

Q:  I'm running O-90 curves on the inside loop to get the least ridiculous (ie, best) appearances in what will inevitably, despite whatever straight I can fit in, be mostly a circle.  But if I'm willing to compromise on appearances because O-72 is more convenient to build and live with...am I frustrating certain locomotive or rolling stock desires later in life that I cannot foresee now as I pour the concrete?

I am newly returning to model RRing, experience limited to being kid-in-the-70s with a few HO and O-27 starter train sets with tracks assembled on floors and the ping pong table.  So now that I'm grown up, I can cut tunnels through my wall and design aerial RR spans for the cathedral space over my little kitchen...I wonder what kind of big brass or other heavy metal O-scale steam engines (or whatever else might be big...and same for cars) --what might I want someday that would make me say:

"Gee Whiz!  I wish I'd built that run in O-90 after all!  I thought I could run ANYTHING on O-72!!"

For example, should I swap out those 4 O-72 switches because, unless the inner circle only runs through them as straights, my otherwise O-90 inner loop will have those switch curves reduce the rating to O-72.  Will I regret that when I want a big train later?  I thought I could run ANYTHING on O-72!

Last edited by Will Wilkin
Original Post

Replies sorted oldest to newest

Thanks John!  That's the kind of re-assurance I need as I push my saws through walls and plywood.  Dave mentions there will be found somewhere something that truly needs bigger than O-72 (I found some more obscure RR modeling websites where minimum curves were all over 100 and I bet the modeling was exquisite).  But I detect vast experience and knowledge in John's summary of the answer, that lots of big trains will run O-72 fine.  I figure, whatever exception that undoubtedly can be found, my train won't be it! 

And now I'm wondering, is my modeling question about the minimum turn radius related to why real locomotives were sometimes built as articulating units?  Was that so they weren't too long as a rigid straight line?  Wouldn't our scale version of that problem be the reason some curves could be too tight?  Probably it comes down to the length of each truck and maybe also the maximum turn angle of each truck?

@Hot Water posted:

In my opinion, ANY of the scale length passenger cars from Sunset/3rd Rail/Golden Gate Depot look, and track, best on curves larger than 072.

I would agree with this comment on curves.  I recommend going as wide as you can get away with on your mainlines at the least.  You should be fine with 072 turnouts.  One of my former layouts had 072 and 080 curves and I should have gone larger.

The only locomotive I have found that likes slightly larger than 072 curves is the true scale GG1 which only Lionel and 3rd Rail have done in 3 rail.  To be fair, they just need precise 072 curves.  Those locomotives are what made clear to me on my current modular 3 rail layout that the outside loop was not quite 072.

MTH, Williams, and Weaver "Scale" GG1s are 1/2" shorter than true scale and have no issue on my roughly 071 curves.

One the flip side the 3rd Rail Jawn Henry runs fine through 072 curves and since I don't own one, I have no idea how.  

There being a difference between "won't run" and "look best".   Perhaps we can answer the question asked?

OK. On our layout, the complete Golden Gate Depot set of Southern Pacific Daylight passenger cars, with the three section articulated diner and the two section articulated chair cars, would NOT negotiate the one short 072 curve section I had, when the full width diaphragms were installed!

Have you considered a compromise between the 090 and o72 like 080 while retaining your existing turnouts just modifying the track plan to accommodate them. Like John and others have stated most everything produced today can handle 072 but looks so much nicer when you go with a wider curve. My tightest curve is 072 then I opened up everything else to 080 or better. I still have issues with my MTH Big Boy and Centipedes on my inside loop due to overhang but the run. Great on the outside loop. As John has stated in the past it may be kind of funny when the Big Boy takes out a string of passenger cars but the car owner will not be a happy camper. Just MHO

i have run my MTH S1 thru my 072 curves with no problems like wise my MTH T1 handles them fine.  As stated earlier I have a set of scale K-Line Heavyweights when I had replacement  diaphragms from Lionel installed they have issues.    

Last edited by RJT

@Will Wilkin - Welcome to the forum -  I have 2 MTH Premier crocodile locos. One is high rail, one is scale wheels, both supposedly will take 072 curves.  The high rail engine runs fine, the scale wheel engine derails as soon as the curve comes into play. (Both run fine going straight.) This is on Ross track. If you forget about running anything with scale wheels, you should be fine, they will take the curves without derailing, but whether they look good is another matter.

One of the things I have learned, is the issue of track radius and diameter and then type of track. O-gauge can refer to semi-scale and scale, but within scale you have high rail (3 rail / 2 rail) [HR] and 2 rail scale [2RS]. Reading the replies I think everyone is assuming you are thinking high rail. As with HO, the 2 rail scale enthusiasts talk in curve radius. High rail enthusiasts talk diameter. HR runs fine on 072 dia, but I think you will find 2RS needs much bigger curves approaching 120 inch diameters - depending of course on the size of the engines. You could have seen articles from either camp.  HR engines can run on just about any type of track, 2RS ideally has solid rail and a flat top surface (no traction wheels for these folk, heresy). In addition 2RS wheels are intolerant of less than perfect track laying and most likely lower quality switches.  Lastly, some of the "look" issue is driven by the length of passenger cars. 21 inches, 19 inches and 12 to 15 inches. I think most high railers would agree that the 21 inch cars (which can be stunning) do not look that great on an 072 curve. Mostly due to the middle of the car body overhanging the inside of the curve.

Its your railroad, you can do what looks good to you.

Non-Responsive Suggestion:  Use easements in your curves; e.g. start at 096, then 080, then 072 at the apex then reverse the radii exiting the curve.

I've recently spent a lot of time running or observing our club's 46' x 20' travelling layout's 3 main lines with constant radius curves of 072, 080, and 096 at the four corners, and I can say the uniformity and symmetry of constant radius curves is BORING.

If your are going to use GG flex track, buy some used curves in the desired radius/diameter to use as guides when you bend the track; or, better, cut templates with the desired easements.

Just my two cents.  It's your railroad; build what  you like.

Last edited by Pingman
@ScoutingDad posted:

@Will Wilkin - Welcome to the forum -  I have 2 MTH Premier crocodile locos. One is high rail, one is scale wheels, both supposedly will take 072 curves.  The high rail engine runs fine, the scale wheel engine derails as soon as the curve comes into play. (Both run fine going straight.) This is on Ross track. If you forget about running anything with scale wheels, you should be fine, they will take the curves without derailing, but whether they look good is another matter.

I will say, dependent on the track type, the MTH scale wheel locomotives can be problematic even if you observe their minimum curve requirements.  I had several of the scale wheel steamers when I was using Fastrack, and they would derail on O72 curves even though the stated requirements were O42 curves.  They ran fine at the club on Atlas and Gargraves track.

@Will Wilkin posted:

I'm building a RR layout with an overall design of an O-72 loop close to 4 walls with another O-90 circle (with as much straight-run expansion as I can fit) inside that.  The 2 loops will be connected at least twice, using 4 switches I have.  For each loop, these are the widest curves I can reasonably fit.  Of course I can always be unreasonable if I want to be, but only if it guides me to the best decision.

My switches are remote Gargraves rated O-72, and except for 6 short straight Gargraves terminal tracks, the rest is Gargraves 37" flex track.

Also, for purposes of the question below, I'm not interested in side or height clearances in this discussion, because they've been covered already in other topic threads I've read here.  From those discussions I've already determined that my side clearances will always be wider than 3.5" from center rail, and height in tunnel run 6" above rails.  So here I'm only interested in the rating of the turn radius, O-72 being a 36" radius.

Q:  I'm running O-90 curves on the inside loop to get the least ridiculous (ie, best) appearances in what will inevitably, despite whatever straight I can fit in, be mostly a circle.  But if I'm willing to compromise on appearances because O-72 is more convenient to build and live with...am I frustrating certain locomotive or rolling stock desires later in life that I cannot foresee now as I pour the concrete?

I am newly returning to model RRing, experience limited to being kid-in-the-70s with a few HO and O-27 starter train sets with tracks assembled on floors and the ping pong table.  So now that I'm grown up, I can cut tunnels through my wall and design aerial RR spans for the cathedral space over my little kitchen...I wonder what kind of big brass or other heavy metal O-scale steam engines (or whatever else might be big...and same for cars) --what might I want someday that would make me say:

"Gee Whiz!  I wish I'd built that run in O-90 after all!  I thought I could run ANYTHING on O-72!!"

For example, should I swap out those 4 O-72 switches because, unless the inner circle only runs through them as straights, my otherwise O-90 inner loop will have those switch curves reduce the rating to O-72.  Will I regret that when I want a big train later?  I thought I could run ANYTHING on O-72!

how is the project coming along

Most everything with hi-rail wheels will run on O72 curves and switches.  The looks of longer cars and locos on such curves are a matter of taste.  A good compromise is to use easements going into and out of 36" radius (O72) segments, if you have the space.  Another trick is to hide the tighter curves.  My layout-under-construction has two hidden horseshoe curves that are 80/72 at the apex, 96/88 halfway through, and above 112/104 at their entry points, on a hidden lower level.  It's a matter of the space you have, the cars and locos you want to run, and your tolerance for exposed track along curves when viewed from above.  A sketch of what you describe would be helpful in providing a more specific answer.

Add Reply

Post
The Track Planning and Layout Design Forum is sponsored by

AN OGR FORUM CHARTER SPONSOR
OGR Publishing, Inc., 1310 Eastside Centre Ct, Suite 6, Mountain Home, AR 72653
330-757-3020

www.ogaugerr.com
×
×
×
×
Link copied to your clipboard.
×
×