Transitioning track centers from 4" on straight to 6" on curves

CJ

I will have a similar issue in front of me requiring action within a month. The lads are swinging hammers and layin rail soon a four track mainline that will have the sense of the NYCRR Water Level Route (NYC-Chicago) will need to be dealt with.

I considered some of the following

1. On an 072 curve the forward deck on my Big Boy extended a max of 3.25" from track CL to the outside by observation

2. My GGD 20" passenger car on an 072-curve extended to the inside of the curve 2.0" by observation

3. In both cases above the overhang became much less as I increased the diameter of the curve by observation

4. The majority of my equipment extends past centerline maximum of less than 70% of the Big Boy and 20" Baggage car

5. While drawing with SCARM I found as you did, that using Ross sectional pieces allowed me to mess around with the geometry. I noticed that using sectional pieces of greater diameter at the curve entry and exit to the straight sections and lesser diameter pieces in the middle of the curve allowed me to simulate a more natural easement. Then I inherited...

6. I was nervous about using Gargraves Flex track however I inherited 4 full cases of track 14 years old unopened. After looking for a workable solution here is what I will try, and I am very much soliciting suggestions and opinions.

A. Using my chalk line, I intend to snap 4 Parallel lines 4.5" apart. (I was going to use 4.0" but that will not work as well with 4-track signal bridges from Zstuff).

B. I will take a nice piece of CVG fir and on the table saw rip 4ea. 10-foot-long thin strips 1/16-1/8" x 1"

C. I will temporarily nail brads on either side of each chalk line and then fit my thin strip of fir between the brads. I will repeat this process for all four tracks. When after manipulating I am satisfied with the easement and spacing and symmetry, I will trace the strip onto my Homasote (tabletop) before removing the strips and the brads.

D. Glue one side of my roadbed to the traced curve, then glue and staple the other half of the roadbed. Then bend the track to fit the roadbed fastening as I go.

If anyone has a better way, please let me know. Thank you, kevin

Oh yeah a problem I have yet to think about, How will I shim to super elevate the curves???

One thing to keep in mind is that the long passenger cars start to swing out while one truck is still on straight track.   You may want to mock up the situation before you make final plans.

Thanks for sharing your experiments, Kevin. I am inclined to purchase some Ross track and run some experiments of my own. I just hate the idea of buying track that I may not use and then just lies around, not even usable as a spare or replacement piece for the layout.

@David Johnston posted:

One thing to keep in mind is that the long passenger cars start to swing out while one truck is still on straight track.   You may want to mock up the situation before you make final plans.

That is a very good point, didn't think about that. I have some 18" cars but always assumed I would never purchase a set of 21" cars. But with the dreyfuss hudson being teased that will probably change very soon!

I stressed about this sort of thing too on my layout. I'm in the process of building the benchwork now. The overhang info on the Bigboy is really handy. I would assume that's the biggest overhang we'll find. I'll try to remember to post back with my own results. I started my outter curve a few inches past the inner curve. Hopefully that gives me the clearance I need.

I first wrote on this subject above hoping that someone might tell me a better way or that my plan had an issue. I hope I haven't hijacked the thread; I hope to be at this point of construction in the next 2 months at that time I will post pictures.

Hoping to make a few things a little clearer.  When you bend a long thin strip of wood the point in the middle between the two fixed ends is where the radius will be smallest and tightest and as you go from that center point to the fixed point the radius increases So in my plan above, I trap the thin strip of wood on edge between brads partially nailed in either side of my parallel lines representing where the track is straight.

My 4 curves are roughly 128 Diameter to 96" Diameter and will be separated by approximately 4-5" to 5-5" my parallels are 4.5" centerline to centerline.

By doing this with all four tracks I can visually find symmetry and clearance distance between as well as having the same easement as real railroads on entry and exit from the curve. I can tweak each strip by changing the start and stop points of the bend and changing the length of wood strip between the two fixed points. Of course, when satisfied I will trace with a marker and proceed with roadbed and track laying.

On these pages I have seen some beautiful track work and have been very impressed with the flex bent parallel and with easement. If anyone has dealt with similar, please post or message me, thank you,

kevin

I draw the centerline of my planned track using CAD then offset the line half the length of the ties to the inside of the curve and print this at a 1:1 scale.  With this line the entire curve is included with a short section of tangent on each end.  I then glue this print to a sheet of 1/4" PVC and with a sabre saw cut along the outside of the line.  The inside of the PVC part is left wide enough to remain stable.  Then I fasten this to by table temporarily and bend the track around the curve fastening it down frequently.

Here is a corner that has 4.25" spacing on the ends and 6" spacing at the apex. Each curve starts 4.25" past the curve to the inside. Each track has the same radius curve.

Steve

Just a thought...you might want to test your two longest pieces of equipment on your curves.

I have 4" inch spacing on my curves.  The outer curve is 96 diameter.  Inter 88 diameter.

My longest 2 cars are 21' long.  No sideswipe.

I'd keep in mind that if you're traveling in the direction of the green arrow, at the point of the red arrow, any larger steamer with an overhang will likely take out stuff on the next track.  I found out with 4.5" spacing on adjacent tracks at our club that my VL-BB cleaned a passenger train with 21" cars right off the track on the outside rail.  The pilot on any articulated steamer is going to hang out until you're mostly on the straight track.

@L & N posted:

Here is a corner that has 4.25" spacing on the ends and 6" spacing at the apex. Each curve starts 4.25" past the curve to the inside. Each track has the same radius curve.

Steve

That's an idea I didn't think of, it looks nice too!

@John C. posted:

Just a thought...you might want to test your two longest pieces of equipment on your curves.

I have 4" inch spacing on my curves.  The outer curve is 96 diameter.  Inter 88 diameter.

My longest 2 cars are 21' long.  No sideswipe.

Very interesting, what's your longest locomotive? My longest equipment will be N&W Y6b/C&O Allegheny (no interest in Big Boy, though I do have a Lionmaster version), and the longest car will be a 21" passenger car. Every time I have asked I have been assured that there will be side-swiping.

@gunrunnerjohn posted:

I'd keep in mind that if you're traveling in the direction of the green arrow, at the point of the red arrow, any larger steamer with an overhang will likely take out stuff on the next track.  I found out with 4.5" spacing on adjacent tracks at our club that my VL-BB cleaned a passenger train with 21" cars right off the track on the outside rail.  The pilot on any articulated steamer is going to hang out until you're mostly on the straight track.

I'm not seeing a picture, but I think I know what you're talking about.

Seems like buying some track and doing a proper test is all but inevitable if I want to be 100% confident in any design.

Glad to see this post.  I hope someone that has built one of the beautiful layouts we see will comment on how they handled the situation.

Not sure if this helps, or just muddies the water, but the attached links are the NMRA Recommended Practices for track spacing.  NMRA RP-7.6 is a calculator that can be used to help figure out clearances.

https://www.nmra.org/sites/def...rances_july_2017.pdf

https://www.nmra.org/sites/def...diagrams_2019.01.pdf

https://www.nmra.org/sites/def...enters_july_2017.pdf

https://www.nmra.org/sites/def...rances_july_2017.pdf

https://www.nmra.org/sites/def...istant_jul_2017.html

BTW everything for O is based on track RADIUS so the low end of tables is approx O65.

@0-Gauge CJ posted:

That's an idea I didn't think of, it looks nice too!

Very interesting, what's your longest locomotive? My longest equipment will be N&W Y6b/C&O Allegheny (no interest in Big Boy, though I do have a Lionmaster version), and the longest car will be a 21" passenger car. Every time I have asked I have been assured that there will be side-swiping.

I'm not seeing a picture, but I think I know what you're talking about.

Seems like buying some track and doing a proper test is all but inevitable if I want to be 100% confident in any design.

Forgot the picture.  The Y6B is a pretty large steamer, might not have the overhang of the BB, but it's not far off.  I also have the Legacy Y6B and the MTH Y3B.

When the front pilot of your articulated locomotive coming from the green arrow direction is at at the red arrow, the overhang to the outside of the curve will be at the maximum.  That's also where you're trying to come together to 4", which IMO is way too close.  I'll be quite surprised if you don't have a problem with that spacing.

You want to also remember, you may actually acquire something with a large over hang, might as well have the layout accommodate it the first time.

Thanks for the links to NMRA I found the index but could not find the data sheets last week.

I've posted video on this previously. My Premier Big Boy boiler overhangs the outer rail by nearly 2.5 inches on an 072 dia curve.  I am planning to lay my double mainline at a spacing of 6 1/2 inches center rail to center rail - maybe a little more.  The NMRA suggests  5 7/32" as a minimum.  Interestingly if you add up the obstacle clearance recommendations you are close to 6 1/2.

Having crashed my new BB into crossing lights and scenery, I am planning for the extra room. Nothing worse than getting a new engine and having to remove stuff in order to run it around.  Extra room is needed at the exit from the curve as the engine pivots on the rear drivers. Rather than make the main straights on a tighter spacing, I plan to keep the separation consistent throughout. 

Never wanting to have a dispute with GunRunner,  seems to me the maximum overhang for the BB extends to the straight section where there is even less spacing. Might be the video. Funny for the RK BB version the maximum overhang was at the cab roof not the boiler.

The overhang lasts well into the straight section, that's certainly true.  My point is at the curves you have a 21" passenger car that's over the inside, they'll very likely meet right at the curve exit, or anywhere the two tracks come closer than around 5.5" spacing.

I have tracks on my upper section that are spaced at 5.5" on the curve, and the outer curve is O90 in diameter, the inner curve O72.  With an 87' boxcar on the outer rail and the MTH Big Boy on the inner curve, I have around 1/4" clearance between the boiler and the side of the boxcar.  For some reason, the MTH Big Boy hangs out more than my Lionel VL-BB, so I use it for the maximum swing tests.  That being the case, and the exit of the curve having a 4" spacing is a recipe for collision, at least IMO.

I am really curious, does anyone have knowledge of how Gargraves and Atlas decided on what sectional curve track sizes to offer?

Atlas O72, O81, O90, O99, O108  -  4.5" center-spacing.

Gargraves O72, O80, O89, O96, O106, O113, O120, O128, O138  -  "variable" center-spacing.

@gunrunnerjohn posted:

Forgot the picture.  The Y6B is a pretty large steamer, might not have the overhang of the BB, but it's not far off.  I also have the Legacy Y6B and the MTH Y3B.

When the front pilot of your articulated locomotive coming from the green arrow direction is at at the red arrow, the overhang to the outside of the curve will be at the maximum.  That's also where you're trying to come together to 4", which IMO is way too close.  I'll be quite surprised if you don't have a problem with that spacing.

You want to also remember, you may actually acquire something with a large over hang, might as well have the layout accommodate it the first time.

One way to help this is to start the curve of the  innermost loop earlier using a wider radius.

@rplst8 posted:

One way to help this is to start the curve of the  innermost loop earlier using a wider radius.

Yep, the basic idea here is that you'll have to do something special at that transition if you want the 4" spacing or you will have a potential conflict.

Re: the Atlas & Gargraves sectional curve size question, I've read that all the Atlas track was designed to maintain the minimum 4.5" center-to-center distance between parallel lines when used.  In fact, if I remember correctly, every curved section of an Atlas O gauge switch designated with an "O" (O45, O54, O72 etc.) will exactly replace a similarly described (O45, O54, O72, etc.) piece of sectional curved track, allowing for easy drop-in for corner sidings.

Sorry, but I have no clue how or why Gargraves chose their sectional curve sizes.  However, since their track has been around a lot longer than Atlas O gauge track, maybe Gargraves 3-rail sectional curve track sizes were influenced by the common radii that O scale model railroaders used?

Chuck