Trains.com

Subscriber & Member Login

Login, or register today to interact in our online community, comment on articles, receive our newsletter, manage your account online and more!

15 and 18 inch radius curves

33564 views
48 replies
1 rating 2 rating 3 rating 4 rating 5 rating
  • Member since
    June 2007
  • 8,783 posts
Posted by riogrande5761 on Wednesday, March 8, 2023 12:51 PM

Another zombied thread raised from the dead.

Rio Grande.  The Action Road  - Focus 1977-1983

  • Member since
    April 2004
  • From: Ontario Canada
  • 3,562 posts
Posted by Mark R. on Tuesday, March 7, 2023 11:58 AM

fwright

 

 
 

Back to the OP.  15" radius works fine with 40ft cars and switchers (they can generally go down to 12").  F-7s, GPs, and 50ft cars will require more care and tuning of track and rolling stock to be derailment-free on 15".  HO model Shays do struggle with 15" radius curves - it depends on how much extendability/compressibility is built into the line shafts.

Fred W

....modeling foggy coastal Oregon in HO and HOn3, where it's always 1900....

 

 

 

I think the OP is long gone .... this thread was started in 2009 and he only made 3 posts !!!

Mark.

¡ uʍop ǝpısdn sı ǝɹnʇɐuƃıs ʎɯ 'dlǝɥ

  • Member since
    November 2002
  • From: Colorado
  • 4,072 posts
Posted by fwright on Tuesday, March 7, 2023 10:37 AM

markpierce
EM-1

I remember an article by one of MR's editors from sometime in the early 60s.  He got an invite for a 4'X6' layout operating session.  He started the report stating what his initial oppinion was, especially when he found out the layout had 15", 18", and 22" loops.

He reported that after several hours, he had totaly forgotten the small radius curves, 5 or 6 car trains pulled by an Akane Yellowstone among other road engines, and an almost total lack of scenery.  It was an operational joy.

Until you can identify the specific month/year/magazine, I'll continue to believe your memory came from a dream.

Mark, he is correct.  The article was done when Linn Westcott was the editor, so had to be from the early '60s.  I didn't start subscribing 'til '62, so it was after that.  Anywhere from 1962-1966.  I've gotten rid of most of my early MR collection so I can't look it up, but I do remember the article.

One of my other favorites from the era was an article about a 36" x 36" HO layout - an oval with 2 spurs, using 15" radius.  The baseboard was a "tray" so scenery didn't have to be fastened down.  The whole idea was changing theme, era, and operation depending on your whim of the day.  Featured in June 1962 MR as a "Changeable Model Railroad" or similar.

Westcott was all about encocuraging the armchair modelers of his day to get up and actually build a layout.  That was the reasoning behind the popular MR Project Layouts of the day.  Lance Mindheim's "No Skills, No Problem" shelf layout and Carl Endt's micro layouts are more modern versions of the "get out of your chair and DO some model railroading".

Back to the OP.  15" radius works fine with 40ft cars and switchers (they can generally go down to 12").  F-7s, GPs, and 50ft cars will require more care and tuning of track and rolling stock to be derailment-free on 15".  HO model Shays do struggle with 15" radius curves - it depends on how much extendability/compressibility is built into the line shafts.

Fred W

....modeling foggy coastal Oregon in HO and HOn3, where it's always 1900....

 

 

  • Member since
    August 2022
  • From: New England (Cape Cod)
  • 126 posts
Posted by DonRicardo on Sunday, March 5, 2023 11:39 AM

A small corner goes well in n scale. Match your rolling stock to your layout, the tighter your radius, the shorter rolling stock you should use.

My n scale layout (40"x88)"has 15 and 16 inch radius, all laid in using flex track, and it handles Atlas 60' 4 wheel truck passenger cars very well, three locos, two GP-40 4 wheel trucks and a RS-3 switcher. All with body mounted couplers

In HO those radii would be nearly double that of n scale.

 

  • Member since
    April 2009
  • From: Staten Island NY
  • 1,734 posts
Posted by joe323 on Thursday, May 5, 2016 6:16 AM

Keep in mind that O scale Lionel at least the stuff I have has truck mounted coupler which is very unprototypical but allows for tight curves.  Good HO equipment has body mounted knuckle couplers that  require larger curves.  You can find some truck mpunted knuckles (Model Power now part of MRC makes some) that might be okay on 15" curves

Joe Staten Island West 

  • Member since
    December 2012
  • 13 posts
Posted by BroadwayPhil on Thursday, May 5, 2016 4:17 AM

EM-1

I can't look the date up right now, I have a 50+ year collection of MR and RMC in boxes in the attic, but I remember the issue was probably between 1961 and 1965.  It was several pages long, with a number of pictures, so it probably was not in the Bull Session, which usually was a single page column.

I don't have the issue handy, but I believe it ran in 1964 or 1965, possibly 1966.  I think Bill Rau was the visitor.  While he wrote the Bull Session column, this was not one of his columns but a regular article written by the owner of the layout (to which Rau added his remarks on the operating session), and included a photo of the layout, which indeed was on a bare sheet of plywood with no scenery and an oversized (Lionel?) station in one of the few spots not covered with track.  There was a track plan.  The larger engines resided on sidings connected to the outer loop.  The layout was full of cars and engines, and did have some unconnected track sections.  The owner also liked the look of his unpainted brass engines.  He used a number of Docksides to switch his yards.  I don't recall mention of any ten- or twelve-coupled engines, which would not have fared well on those curves.  Despite extreme overhang two long articulated engines were able to pass each other in opposite directions on adjacent loops.

There was an editor's note that No. 4 turnouts had a much larger radius than 18 inches, and so the articulateds would not have a problem with them.  (In N scale, for instance, an Atlas "standard" turnout is 19-inch radius, which corresponds to 35-inch radius in HO, while a 9-3/4-inch radius curve corresponds to 18-inch radius in HO.)

  • Member since
    September 2014
  • From: 10,430’ (3,179 m)
  • 2,100 posts
Posted by jjdamnit on Wednesday, May 4, 2016 3:31 PM

Hello all,

carl425
I don't think you created a problem with what you've done, but you haven't created some new technique worthy of passing on as advice to others either.

Isn't that for other modelers to decide?

Hope this helps.

"Uhh...I didn’t know it was 'impossible' I just made it work...sorry"

  • Member since
    August 2013
  • From: Richmond, VA
  • 1,890 posts
Posted by carl425 on Wednesday, May 4, 2016 8:15 AM

jjdamnit
"Uhh...I didn’t know it was 'impossible' I just made it work...sorry."

Nobody said it was impossible, just that it wasn't a good idea.  The fact it didn't blow up doesn't mean it "worked" as you describe it.

Because the straight sections are much shorter than a car length, they are not going to cause the normal transition issues.  All you have done is created an irregular curve of a larger effective radius than you would have had normally.

I'd expect it probably looks funny because of the short sections of straight track interrupting the flowing curves typical of a real railroad.  You'd have been better off making a smooth curve with real easements out of flex track using the same real estate.

I don't think you created a problem with what you've done, but you haven't created some new technique worthy of passing on as advice to others either.

I have the right to remain silent.  By posting here I have given up that right and accept that anything I say can and will be used as evidence to critique me.

  • Member since
    September 2014
  • From: 10,430’ (3,179 m)
  • 2,100 posts
Posted by jjdamnit on Tuesday, May 3, 2016 6:50 PM

Hello all,

cuyama
The movements will be more abrupt with the straight sections in there than having one curve leading into another directly (assuming these are in the same direction and it's not an s-curve).

I defer to my signature...

"Uhh...I didn’t know it was 'impossible' I just made it work...sorry."

Hope this helps.

"Uhh...I didn’t know it was 'impossible' I just made it work...sorry"

  • Member since
    December 2015
  • From: Shenandoah Valley
  • 8,867 posts
Posted by BigDaddy on Monday, May 2, 2016 4:52 PM

posted in the wrong thread.  move along, nothing to see here

Henry

COB Potomac & Northern

Shenandoah Valley

  • Member since
    February 2015
  • 20 posts
Posted by BobVegas on Monday, May 2, 2016 4:46 PM

Thanks I will check it out

 

  • Member since
    February 2002
  • From: Mpls/St.Paul
  • 13,278 posts
Posted by wjstix on Monday, May 2, 2016 4:33 PM

One thing you could try, is looking at Kato HO Unitrack. It's sharpest curves are 16-7/8"R and 19-1/4"R. Should pretty much fit the same space as 15"-18"R curves, but a little more gradual.

Stix
  • Member since
    December 2001
  • From: Northern CA Bay Area
  • 4,387 posts
Posted by cuyama on Monday, May 2, 2016 1:53 PM

See also the recent posts by the Original Poster on another thread:

http://cs.trains.com/mrr/f/11/t/256330.aspx

  • Member since
    December 2001
  • From: Northern CA Bay Area
  • 4,387 posts
Posted by cuyama on Monday, May 2, 2016 10:58 AM

jjdamnit
With 15- to 18-inch I use three of each. To make a smooth transition between the different radii I put a short section of straight track between the two quarter circles; typically 1- to 2-inches. Making an asymmetrical curve of 18- and 22-inch sectional pieces I uses three 18-inch sections to four pieces of 22-inch radii. Again I use a short section of straight track between the two quarter curves; 1- to 3-inches. The purpose of the short sections between the quarter curves is to allow the cars to transition from one radii to the other without abrupt movements, possibly causing derailments.

The movements will be more abrupt with the straight sections in there than having one curve leading into another directly (assuming these are in the same direction and it's not an s-curve).

In any case, this would be handled more smoothly (and more simply) with flextrack.

DrW
  • Member since
    January 2008
  • From: Lubbock, TX
  • 349 posts
Posted by DrW on Sunday, May 1, 2016 6:13 PM

jjdamnit

With 15- to 18-inch I use three of each. To make a smooth transition between the different radii I put a short section of straight track between the two quarter circles; typically 1- to 2-inches.

Honestly, I fail to understand the logic of this approach.  To make a smoother transition between the straight track and the 15" curve, you put in a section of an 18" curve.  That part is easy to understand; your train goes from straight into an 18" turn and then a 15" turn.  Why would you then put a straight between the 18" and 15" curves?  It gives you a straight-18"-straight-15" transition, containing the straight-15" transition you wanted to avoid in the first place.

  • Member since
    September 2014
  • From: 10,430’ (3,179 m)
  • 2,100 posts
Posted by jjdamnit on Saturday, April 30, 2016 11:13 PM

Hello all,

RA1
Will it help if I ease into the curve with 18 inch radius track on each end and only use 15 inch radius in the middle of the curve(?)

It depends...by putting a segment in the middle of the curve this changes the angle of the ends from a true 180º to a greater or lesser angle. If you are trying to replicate a true half circle (180º) this won't work unless you tweak the ends. 

On my 4'x8' tabletop pike I use what I refer to as asymmetrical curves, be it 15-inch to 18-inch or 18-inch to 22-inch radii sectional track.

Sectional track is divided into segments of a circle. There are 12 segments in a 15-inch radius circle, and 12 segments in an 18-inch radius circle. In a 22-inch circle there are 16 segments. 

I don't put a different radii in the middle of half circle. Rather, I put two quarters of the circles together.

With 15- to 18-inch I use three of each. To make a smooth transition between the different radii I put a short section of straight track between the two quarter circles; typically 1- to 2-inches.

Making an asymmetrical curve of 18- and 22-inch sectional pieces I uses three 18-inch sections to four pieces of 22-inch radii. Again I use a short section of straight track between the two quarter curves; 1- to 3-inches.

The purpose of the short sections between the quarter curves is to allow the cars to transition from one radii to the other without abrupt movements, possibly causing derailments.

Yes, you can combine different pieces of sectional track. Just remember that each abrupt transition is a possibility for derailment.

If you really need non-standard curves that sectional track can't provide consider comercially available flex track, or my tip on DIY flex track:

http://cs.trains.com/mrr/f/11/t/256138.aspx

(Highligh the link and then Right Click to open link.)

Hope this helps.

"Uhh...I didn’t know it was 'impossible' I just made it work...sorry"

  • Member since
    December 2001
  • From: Northern CA Bay Area
  • 4,387 posts
Posted by cuyama on Saturday, April 30, 2016 7:49 PM

BobVegas
I want to take this 8X12 O gauge and make it a 4X8 or 5X8 HO scale, can it be done? Here is the link;
http://ctt.trains.com/how-to/track-plan-database/2014/10/big-steam-in-the-coal-fields

Unfortunately, no. O-31 O Gauge curves as used in the linked design are 31” diameter to the outside of the track. Converting that to radius (measured to the center of the track) as used with scale layouts equals just under 15” radius (14.875”). Translating that to HO scale (48/87.1) yields an equivalent radius of just over 8” in HO, much too sharp for typical equipment.

Lionel Fastrack turnouts (track switches) are also quite sharp relative to typical HO scale turnouts.

As others have noted, O Gauge trains are engineered to go around these sharp curves by making compromises to scale dimensions and appearance.

For all these reasons, HO scale will likely not be as space-saving as you hope compared to O Gauge, and certainly not half the size for a similar layout versus O Gauge layouts designed with tighter O-27, O-31, or O-36 curves.

To look at it the other way around, HO scale 15” radius curves that are considered very sharp would be about equal to 55” diameter in O Gauge, so a little larger than O-54. 18” radius would be about equal to 66” diameter in O Gauge (between O-54 and O-72).

The key issue is the difference in the way most scale trains are engineered versus many O Gauge models.

  • Member since
    September 2003
  • From: California - moved to North Carolina 2018
  • 4,422 posts
Posted by DSchmitt on Saturday, April 30, 2016 6:17 PM

BobVegas

I want to take this 8X12 O gauge and make it a 4X8 or 5X8 HO scale, can it be done?

Here is the link;  http://ctt.trains.com/how-to/track-plan-database/2014/10/big-steam-in-the-coal-fields

 

Rob

 

NO!

 
  • Member since
    August, 2013
  • From: Richmond, VA
  • 895 posts
Posted by carl425 on Saturday, April 30, 2016 4:38 PM

 

 
SouthPenn
HO stands for Half O, so it would be 4 X 6. Good to go.

 

Yeah but... Lionel locomotives and rolling stock are designed to run on WAY tighter curves than HO stuff is.  The Lionel plan (did you miss the fact that he said Lionel?) he's working from could have curves as tight as 27" DIAMETER (that's what O-27 means).  Almost NO HO stuff will run on half of that.

Here's an example of an 8X12 Lionel plan I found online.  The inside curves are 36" DIAMETER.  That would come out as a 9" radius if you halved it to fit on a 4x6.

 

I have the right to remain silent.  By posting here I have given up that right and accept that anything I say can and will be used as evidence to critique me.

 

 

I tried to sell my two cents worth, but no one would give me a plug nickel for it.

I don't have a leg to stand on.

  • Member since
    March 2013
  • 427 posts
Posted by Colorado Ray on Saturday, April 30, 2016 3:17 PM

wjstix

One of the more interesting presentations I ever attended was given by a university professor maybe 20+ years ago at a regional NMRA convention. One of the things he talked about was how people forget that Mallets were designed as a way to get big engines around curves. He had grown up in the coal country in West Virginia and said it was amazing how tight a curve some of those big engines could go around, with a lot of overhang.

The 3 foot narrow gauge Uintah Railway on the Colorado/Utah border had 66 degree curves (91.8 ft radius - 12.65 inch HO) and ran 2-6-6-2T mallets.  Grades were as steep as 7.5%.  Must have been awesome to see them in action.

Seems like the best advice is if you're space limited, do what you have to do, and choose appropriate era and equipment.

Ray

  • Member since
    February 2015
  • 20 posts
Posted by BobVegas on Saturday, April 30, 2016 2:05 PM

I want to take this 8X12 O gauge and make it a 4X8 or 5X8 HO scale, can it be done?

Here is the link;  http://ctt.trains.com/how-to/track-plan-database/2014/10/big-steam-in-the-coal-fields

 

Rob

  • Member since
    October 2001
  • From: OH
  • 17,574 posts
Posted by BRAKIE on Saturday, April 30, 2016 3:05 AM

BobVegas

Hello,

Ok so I also have limited space and just went from Lionel to HO scale, space issues, the wife wanted the garage back! And I have a 4X8 table and want to replicate the layout I had with Lionel to this HO, it will work but only with 15 inch curves. Any suggestions, I really want this to work but I don't and cant get any more room.

 

Rob

 

 

15" curves will work with 4 axle locomotives or a 2-6-0 or 2-6-2 steam engine and nothing longer then 40' cars.

However.

With that said why not use 18" curves which is far better then those 15" curves and will give you up to a small 6 axle locomotive like a SD35 or up to a 2-8-2 and 4-6-2 steam engines 50' freight cars and short passenger cars like ConCor or Athearn.

Larry

Conductor.

Summerset Ry.


"Stay Alert, Don't get hurt  Safety First!"

  • Member since
    April 2005
  • From: West Australia
  • 2,217 posts
Posted by John Busby on Friday, April 29, 2016 8:39 PM

Always-always avoid R1 curves like the plague thats 14 5/8" for the UK and AU and 15" US.

They turn a model railway into a toy railway and place's far to many restrictions on what you can run.

And the manufacturers don't often put min radius information on the box so it gets very hit and miss when purchasing stock for the railway.

And technicaly a shop only has to acsept returns if something is not fit for purpose and buying something that wasn't designed to go round 15" radius isn't covered by that.

The caviat being in an industrial setting at ultra low speed they (R1 curves) can look right.

A lot of things will still get round 18" at normal track speed however at 15" radius that list gets very short  on what will get round at anything like normal track speed if it gets round at all.

Unless you are doing a very sleepy back water short line or purely industrial line with very small locomotives and cars 15' radius just won't cut it.

Try and get larger curves in visable areas if you can if you can't use the scenery to try and break up the view of the sharp 18" curves.

Thats my 50c + GST worth on the subject

regards John

  • Member since
    December 2009
  • 94 posts
Posted by kh25 on Friday, April 29, 2016 3:38 PM

Hello I had been in the progress of building an ho scale 34"×80" layout all main line curves are a little less than 15 curves. I say less because I started with atlas 15R snap track and spread the tie spacing creating curves less than15R I ran 40' and 50' cars the athearn rtr 50' cars ran better than some of the early 50' kits. I used a Bachmann GP7 which ran great on the curves and did not look weird.now the layout is in storage.

  • Member since
    May 2010
  • From: SE. WI.
  • 8,230 posts
Posted by mbinsewi on Friday, April 29, 2016 2:46 PM

Well, OK Bob, first, welcome to the forums, and, you probably could have started a new thread, but no problems, I don't know what your track plan is, but for a "main line" on a 4'x8', you could use 18" radius, which opens up a few more options, but if your plan needs to use 15", when I got back in the hobby, early 80's with my young son, I was able to "splurge" and by a new Athearn SW1200, and it would handle 15", but for cars, if one at a time, nothing longer than 50', but 40' was more the norm for any more cars, such as a train of 4 or 5.

The 15" radius track was short spurs off of a 18" radius oval, that took up the outside area of the 4'x8'.

Mike.

  • Member since
    April 2003
  • 305,206 posts
Posted by Anonymous on Friday, April 29, 2016 2:33 PM

15" curves are quite tight and you won´t be able to run anything larger than a 4-axle Diesel and 40 ft. cars, providing you change the couplers from body-mounted to truck-mounted.

Not really recommendable!

  • Member since
    February 2015
  • 20 posts
Posted by BobVegas on Friday, April 29, 2016 1:56 PM

Hello,

Ok so I also have limited space and just went from Lionel to HO scale, space issues, the wife wanted the garage back! And I have a 4X8 table and want to replicate the layout I had with Lionel to this HO, it will work but only with 15 inch curves. Any suggestions, I really want this to work but I don't and cant get any more room.

 

Rob

  • Member since
    August 2008
  • 357 posts
Posted by EM-1 on Monday, August 17, 2009 10:04 PM

Akanes are most definitely brass.

I used to drool over their EM-1 at a local hobby shop when they first came out.  $99.98, and I was working an average 20 hours per week at $1.37/hr while going full time to college.  Never could find the money when I could have bought one, and could never find one when I had the money.

The hinging of the two engines on the models nomally lets the model go through much tighter curves than the prototype could.  The front engine rarely has to cary any significant portion of the boiler weight.  And I have often watched DVDs of the Big Boy going through yard trackage and curves, and it seemed to me that the offset on the front engine occasionally swings almost as much as my Y-6 does on 18" curves.  The mechanical limitation is the rigid wheelbase of any of the individual engines.  Some (a lot) years ago, the father of a friend scratchbuilt a PRR 0-8-8-0 from an RMC article in RMC by Bill Schop.  Used the 51" Mantua drivers.  It was capable of 12" curves.  Each engine had one set of blind drivers.

It would be interesting if someboy with a few of the larger, especially brass, would build a small test track with say, 14". 15", 18", 22", and 24" curve segments and run some locos on them as a test.  In this months MR, they list a fairly large 8 drivered locomotive, the MTH J-1 4-8-4 as having an 18" minimum.

I'd say that you have to build a layout to fit the space you have, then select the motive power to fit the curves.  For turn-of-the-Century steam, 4, 6, and 8 driver locos.  For later steam, smaller drivered 6 and 8 drivered locos.  Diesel era, 4 wheeled Geeps, Alcos,things like the GE 44, 45, and 70 ton switchers, EMD SW series.  The old Model Trains magazine even had an article about a shortline that used a small 4 wheeled diesel that looked very close toan old diesel that used to be advertised by the old Penn Line company that was shown off running around a loop of track that used a Silver Dollar for the inner rail.

Just do what makes it fun and enjoyable for you.  If space is limited, don't start taking prototypical appearance too seriously.  You'll never have much satisfation or  fun.

  • Member since
    February 2005
  • From: Vancouver Island, BC
  • 23,272 posts
Posted by selector on Monday, August 17, 2009 6:49 PM

Yes, Stix, and isn't an Akane a brass engine?  It just seems unlikely to me, but I don't have any experience whatsoever with brass engines....nada.

-Crandell

  • Member since
    February 2002
  • From: Mpls/St.Paul
  • 13,278 posts
Posted by wjstix on Monday, August 17, 2009 11:25 AM

selector

But....but.....but a Yellowstone has 16 drivers split between two engines.  15" curves?  

-Crandell

One of the more interesting presentations I ever attended was given by a university professor maybe 20+ years ago at a regional NMRA convention. One of the things he talked about was how people forget that Mallets were designed as a way to get big engines around curves. He had grown up in the coal country in West Virginia and said it was amazing how tight a curve some of those big engines could go around, with a lot of overhang. I think 15"R for an HO Yellowstone might be too much, but still....

Stix

Subscriber & Member Login

Login, or register today to interact in our online community, comment on articles, receive our newsletter, manage your account online and more!

Users Online

Search the Community

ADVERTISEMENT
ADVERTISEMENT
ADVERTISEMENT
Model Railroader Newsletter See all
Sign up for our FREE e-newsletter and get model railroad news in your inbox!