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I am thinking of basing my On3 railroad on Malcolm Furlow's HOn3 classic from 1984 the San Juan Central. The space required

will be roughly 16 x 20. Would anyone who knows of that railroad be able to redner an opinion on whether

MMI locos (K-27's or K-36's) would be able to handle the curves required? I do not know the exact radii that

I would have to build in converting from the HOn3 plan to On3, but I know the radii would have to be at least





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Hi Eliot,


The San Juan Central has always been a favorite of mine.


The original in HOn3 was roughly 8'x10' with a 15" minimum radius.


Doubling everything to 16'x20' is a good rough estimate for the space required in On3, but that would only allow 30" minimum radius.


While I know you would not need anywhere near 48" radius, you may need more than 30", which would increase the space required. As you know, On3 engines usually take a wider radius than those On30 Bachmanns that are compromised in design to take HO 18" radius track.


I did some quick searching and saw a few references to the K-27 needing 36" or thereabouts.


What you'll have to do is first get a firm number on what those engines require, and then redraw the track plan using those curves as a minimum. This dinosaur still uses pencil, compass and ruler, but one of the software packages would give a more elegant plan.


Having a clean slate to start again can really be exciting. Looking forward to following your progress.



Last edited by Jim Policastro

Many thanks, Ron and Jim and Happy New Year to both of you.

i recently acquired Tony Koester's new Narrow Gauge building guide and his sources indicate O scale K-27's and K-36's need a 48" radius to run well and look good. Malcolm Furlow's curves will have to be reworked because they are too sharp based on Tony Koester's sources. It might come to pass that I will have to redraw the plan. In any case, there are very few narrow gauge track plans I have come across that neatly fit a 10'x20'.


This Bronx boy ne'er seen no narrow gauge locos pullin' coal on the Grand Concourse.

Last edited by Scrapiron Scher

But, I hate to admit that I'm old enough to have seen Mack, chain-drive, solid rubber tire trucks delivering coal to most of the apartment buildings on my College Ave. block not far from the Concourse!


Those 48" curves might look nice, but they will eat up your train room space. For the real narrow gauge "look", tighter curves winding through the mountains might be better.


You could just eliminate one or two of those twisty over-unders in the original plan to gain some space and still get the narrow gauge feel to the layout.


I bet you could handle anything ever made in On3 with 38" or 40" curves.




Last edited by Jim Policastro

Wonder if a tighter radii would work if you modeled this as C&S (smaller Moguls?) or

Denver, South Park, and Pacific, with Mason-Bogies, 4-4-0's, and 2-6-0's.   (looking

at Mason-Bogies, I am not sure they would allow you to tighten the radii much, but

C&S 2-6-0's might.  And maybe any of these other road models are harder to find or

non-existant vs. D&RG locos)


FWIW...a digression:

I elected to go with "On30 fine scale" (defined in an On30 annual editorial as On3 equipment on On30 track with couplers at On3 height/size) because of On3 radius issues.  The width difference between On3 and On30 track is almost impossible to see.


I'm running three MMI On30 locos (C-19, K-27, and K-28), a BLI C-16, and a modified B'mann 4-6-0 with a minimum main line radius of 28" on Micro Engineering flex track & turnouts.  The rolling stock is mostly San Juan Car Co. and AMS using Kadees and the wheel sets changed to On30.  The Bachmann pieces (cabooses/steel sided hoppers) have been modified to handle Kadees at On3 height.


My free lanced prosperous road (Port Anne Western) is located in the mid-Atlantic region running from the Tidewater to the Blue Ridge Mountains.  I've removed the C-16/-19's tender deck air tanks to make them look a bit less D&RGW...


Here's the C-19:


b344 jan15 4


Images (1)
  • b344 jan15 4

Thanks for the inout everyone.

i have plenty of On3 equipment.

i purchased a collection several years ago from a fellow on the Forum.

i have three MMI On3 locos including a K-27 and a C-19. I am trying to

determine the radii I will need for good operation and that looks good to

the eye. I can design from the ground up by I love what Malcolm Furlow did.

my railroad does not have to be D&RGW but I am moving in that direction.


Eliot "Scrapiron" Scher

I can't speak to ON3 but I can speak to MMI and some others.  What is advertised as minimum is often the loco or car all by itself.  The issue we are having (ON30 layout) is that when coupled to rolling stock or what ever we find that if it says 28 min they mean 30 ish!  If they say 32 then mean 35 ish!  It's always around 2 or 3 extra inches added to the RADIUS.  Adding some weight helps but we had truck clearance issues with San Juan and some others.  If you turn the truck to run at the minimum the FLANGES hit the under body detailing.  On the San Juan cars we did a little trimming of the truss rod ends and a little thinning of the sides of the coupler pockets to get them to RELIABLY navigate 32 inch radius.  Hope this helps.  Russ

mwb and Russ,


Yes, the information all helps.

All of the ideas will help me work toward a good solution. Russ, what you are experiencing with the minimum radius recommendations of the manufacturers is EXACTLY what I need to avoid. All of my cars are San Juan Central. They are gorgeous cars, but I don't want to do any trimming. I think I am looking at 48" radii as a minimum. If that becomes true, I will have to redraw the San Juan Central track plan. Suggestions welcomed.



48 is to big for a minimum.  The reason ON30 is tighter is the wheels are SLIGHTLY closer together I.E 30 inch versus 36 inch spacing.  So it is even more critical as the under body clearances are well you see.  The easiest thing to do is lay a couple pieces of flex track bent to what you WANT or NEED and run some car tests.  I run 2 rail O scale on 48 so that is to big for your minimum.  O believe with a little weight in the cars and 34 or better will work.  Russ




Using this track plan it is easy to see why 48" radii will be difficult to include.

I know that 48" radii may not be the bare minimum for MMI locomotives, but

I also want the type of operation where the loco looks as authentic as possible.


Look at the two loop curves diagonally opposite on the track plan for the San Juan Central.

I will need to broaden those. The lower left loop should be fairly easy, but how would you handle the upper right loop?



San Juan


Images (1)
  • San Juan



It all depends on the look you want.


It's either trains winding through the mountains on tight curves on ledges cut into a cliff face where only narrow gauge track would fit.....or it's trains on wide, sweeping curves.


It's hard to get both without having a supermarket-sized layout. Malcolm Furlow was going for the tight, windy look on his San Juan Central, so it will be tough to accommodate big curves with the SJC as a starting point .




Today I bought my first DCC system, an NCE Power 10R Wireless control. I was able to see one at the Big E. Interestingly, it needs an 18 volt/10 amp power supply but I stead of using a Z-4000, I bought the "Dedicated NCE "Brutus" which will plug right in instead of me having to split wires from the Z-4000.


i discovered I have an MMI die cast K-36 in green and two C-19's.

My wife, Blessed Be She, is buying me two Precision Scale brass passenger cars in DRG yellow.


i declare, with the power divested from me, I am a two Railer.


now, all I need is a layout 

Last edited by Scrapiron Scher



If you wanted to do something different than Colorado style mountain narrow gauge, look into the Ohio River & Western which ran from Belaire Ohio on the Ohio river eventaully to Zanesville in the middle of the state through some really rolling country called the "Dark Hills".    Basically Applachian foothill country was its home.   It lasted from the 1870s into very late 1920s.   It was eventually bought by the Pennsy I to get control of the coal fields they owned.   but the coal was never really mined much.   It was a common carrier.  


There is also the Washington and Waynesville in Pa which was much shorter but lasted about as long.


Just some thoughts for long lasting easter narrow gauge other than the EBT.


Malcolm was a real inspiration when I was modeling large scale narrow gauge.  I still have my copy of  HO Narrow Gauge Railroad You Can Build: A Narrow Gauge Project Railroad.


Elliot if you get a chance, definitely attend a Narrow Gauge convention.  They are spectacular.


Narrow gauge is fun.  I don't know if you've come across this website yet but the videos are excellent.  Lex Parker is a real artist.  


I came across the Aspen Modeling Company looking to model a stock yard.

Hi Elliot • My layout is 42 inch, I should have made the bench work handle 72 inch. If you can change your bench work and have the floor space. Go with 72 inch. The long trains look so much better. PS - My wife is from Ouray, CO - What cities are you going to have on this layout? I have spent a lot of time in this part of the USA. The 72 inch may not look prototypical.

     My Two Cents

     Gary, from Michigan

  Click Photo to enlarge.

San Juan Central


Images (1)
  • San Juan Central


I talked with Malcokm when I was out at Taos, NM with my wife, Ginny. We went into a very expensive art gallery that was featuring his work. Malcolm is now quite a famous artist living on a large ranch out there. His scenery was spectacular. I will be showing you some scenery work done by a fellow who models narrow gauge that is also amazing.



Thanks for the suggestions. I have not yet decided what will be included on the layout. I am still mourning the loss of the Munoz Lines. I am now a two Railer with a three Railer brain. I am thinking Colorado, but it is likely the railroad will be a hybrid.



Your layout looks spectacular. That is one of the parts of narrow gauge modeling I look forward to. Long, spindly bridges and cool, trundling trains.



We're gonna get to work on this !



Last edited by Scrapiron Scher

good choice.  i just dismantled my On3 layout.  i ran 44" radius and MMI k36 had no issues at all.  my link to, well what is now my previous layout, is below.  there is also a thread on the 2 rail forum around the demolition of it.  great choice to model after;  the MMI stuff ran for 8 years on my layout with no issue (i DCC'd all 9 locos). they ran flawless.

 I have attempted to sketch a version of the San Juan Central with two return loops that would have at least a 44" - 48" radius. Please compare what I have drawn to the original track plan by Malcolm Furlow. My redraw is not as dramatic, but it will allow for the operation of large Mikados like a K--27 or K-36. I am trying to contain the overall dimensions of the layout to 10' x 20' .





San Juan Central Redrawn

San Juan Track Plan



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  • San Juan Central Redrawn
  • San Juan Track Plan
  • SJCTopView
Last edited by Scrapiron Scher

Opinion: In the final analysis, only your opinion will matter.  BUT, since you asked:


* Your plan enters the main line in the wrong direction so you'll be going through your representative towns in the reverse order and reverse direction. In other words, you leave Montrose and then pass through Tin Cup, and then the "Rio Grande" (the back siding) area and then start continuous running. Whereas the actual SJN, you leave Montrose, pass through the "Rio Grande" area, then Tin Cup, then onto the scenic portion containing the outside viewed curve to start continuous running.


* You're losing the scenic portion that contains the outside viewed curve scene that was quite characteristic of the SJC.


* I think the desire to hold to the large radius to accommodate the larger narrow gauge engines is really putting the crimp on your track plan.


HOWEVER... the only one you need to please is YOU.


Best of luck in your endeavor! 



Last edited by laming

laming . . .


Very insightful observations. Though I am certainly concerned about the reverse running, I am even more concerned about losing the scenic portion to which you refer. Malcolm's minimum radius would translate to a 30" radius for O scale which would require that only the smallest locos would make it anywhere. 


Now, the truth. I can make the layout bigger than 10' x 20' so there are more design possibilities that will reveal themselves. I am determined to find a way to maintain Malcolm's beautiful densign and also do my K-36 thing. Will it happen . . . ? Stay tuned.

Last edited by Scrapiron Scher
Mike, you hear much from Dr. Steve??  is he still in o scale or just big scale?
Originally Posted by zak98:

good choice.  i just dismantled my On3 layout.  i ran 44" radius and MMI k36 had no issues at all.  my link to, well what is now my previous layout, is below.  there is also a thread on the 2 rail forum around the demolition of it.  great choice to model after;  the MMI stuff ran for 8 years on my layout with no issue (i DCC'd all 9 locos). they ran flawless.


 Please take this as a bit of constructive suggestion.  I might be totally out of line but here's where I think changes are needed.


Furlow did some important things.  He took a John Allen theme, upgraded it using 1980's techniques and pushed realism out of snap track designs.  He could also expertly manipulate a camera...his forced perspective shots were quite innovative back then.  I consider his talent as being half model craftsman, half master of illusion.


If I understand Eliot's level of experience correctly I believe a layout based on the above restrictions would be below his standards.  Once you limit a layout to circles without easements, short sidings and geometric design the end result looks forced.  With the improved methods and vast variety of NG today I'd be ditching snap track designs and maybe even learning the art of hand laying.  It certainly isn't a large, overpowering undertaking with multiple tracks and levels.   At least use flex track all around and many curved turnouts.


On the other hand, Furlow's original track design is a perfect starting point and losing the inside curve at the Rio Grande section would really kill interest.  If you must maybe this would be a compromise?  Not a sectional piece of track to be found.  Sorry, but I don't convert easily from simple pencil and paper.




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