# 22" vs. 24"?



## Smokinapankake (Sep 8, 2011)

So I've been planning a double decked HO layout and was debating between 22" radius and 24" radius curves. I'll be doing cookie cutter construction and so will require track boards. Probably 90% flex track. A helix to go from lower to upper level. I'll also be running mostly Athearn 6 axle locomotives with 85' passenger cars, but also some 4 axles with freight (40, 50, and 60').
Problem is, the 6 axles tend to pull the cars off the track on 22" curves unless you weigh the crap out of them. Also, the locomotives don't really like to couple/uncouple on those kinds of curves. 24" isn't really much better for coupling.

Some pros of the 22": 
Easy to make curves - sectional track is readily available
To make a helix with 2-1/2" wide track boards can be cut out of a standard 4x8 sheet of plywood. 
Does not use up as much space.
22" cons:
Coupling is more difficult. 
6 axle locos tend to pull the cars off the track unless you weigh them down heavily. Not really an issue as I'll be running short trains and gradual grades. 
Not super attractive-looks too sharp. To my eye, anyway. 

Some pros of 24":
More gradual curves are more realistic looking. 
Coupling/staying coupled less of an issue.
Larger locomotives run better, don't pull the cars off the track on the curves. 
24" cons:
Uses up more space.
Helix building will require more material - don't know where I can find sheets of plywood larger than 4x8 to cut a circle of trackboard from. 
Have to use flex track. Not an issue as I've built lots of layouts with flex before - mostly in N scale but the procedure is about the same for HO.

I've got about 21 ft by 14 ft to work with so space isn't really an issue. 

Any thoughts or am I missing something?

Thanks for the help!


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## sstlaure (Oct 12, 2010)

With the space you've got I'd go 24" minimum and go as big as you can throughout the layout. It will operate more reliably with the larger curves.

You don't need to cut complete circles out of the plyboard to make a helix. I went 26" in my helix and I was able to cut 270 degrees of circle in a single swath around the board. Doing this also staggers the joints within the helix which can help in building it. Take a look in my build thread (14x16) and you can see the helix construction I used. I simply marked the centerline of the curve at 26" then made the wood strip 4" wide (24"inner, 28" outer curve) and cut with a jigsaw.

You'll get 1 big curve and a few smaller curves out of a 4x8 sheet.


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## tjcruiser (Jan 10, 2010)

And don't forget that if you use MDF instead of plywood, your standard sheet size is 49" x 97" ... a precious inch larger than a sheet of ply. Might help with those 24" turn pieces.

Also, plywood mfrs also make oversized plywood sheets ... 5' x 9', for example. I've never bought an oversized sheet, so I'm not sure if this is something you could special-order through your local lumber yard. Worth checking into, though.

TJ


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## sstlaure (Oct 12, 2010)

Even with a 49" wide piece of plywood (or mdf) you're not going to be able to do full 360 cuts @24" radius. Leaving 2" outboard of the track centerline would give you 22" radius if you wanted a 4" wide roadbed.

I'd much rather buy an extra piece of plyboard and have curves that operate better.


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## Massey (Apr 16, 2011)

What engines do you have that throws the cars off? I had a Genesis SD70MAC that would do that when I tried to go around 18" radii, but it was fine on anything 20+. Aside from that you should give yourself the largest radii you can afford and the larger the better. I wish i could have done at least 22" on my layout I dont really like 18" but if I wanted a layout I needed to make it 18".

Massey


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## Smokinapankake (Sep 8, 2011)

I run mostly Athearn 6 axle stuff with the vast majority of that being SD40-2's. Body mounted couplers + body mounted couplers on the cars typically spell disaster on sharper radii curves. 

I use Accu-Mate couplers and on these particular locos I use the longer shanked version which helps, but find that I have to over weigh the shorter freight cars to keep them from pulling sideways off the track on 22" and smaller radius turns. I currently have an oval with 22" radius turns and will have to do some more testing, but preliminary investigation suggests that a larger radius is preferable if I can pull it off. 

I still need to secure the right of way from Mrs. Smokin before I actually lay out any cash so wish me luck in that department as well.

I'm leanin' towards the 24" radius in spite of the extra material required. If it helps things run smoothly rather than causing undue frustration then I'm all for it. This is supposed to be fun, right?


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## Massey (Apr 16, 2011)

I have 2 BB SD40-2s which the RTR versions are almost identical to and they can take 18" just fine with out throwing anything off the tracks. One of those SD40-2s has the plastic couplers that came with the kit and the other had a Kato in the nose and Kadee in the rear pilot. Neither are extra long. I have no problems.

Massey


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## Smokinapankake (Sep 8, 2011)

I must be doing something wrong. They can pull the 18" radius, but to pull cars behind them they just tend to pull the cars to the side, then the cars come off the track. 
At any rate, since I have the room, I'll probably go with 24" radius.


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## jzrouterman (Nov 27, 2010)

Smokinapankake said:


> Any thoughts or am I missing something?
> Thanks for the help!


I had a simular problem with some of my cars when being pulled or pushed by my SD40-2s. But only my problem was only with 18" radius curves. The 22" radius track worked fine. So rather than to tear down the layout, redesign it and start again. I purchased a 40' car from Model Power. Their couplers are "truck mounted" rather than body mounted. 

I replaced it's wheels with Protos, installed different couplers, installed a (car length) weight strip (slightly thicker metal). The metal that the weight strip is made of is available in 3 and 4' lengths and in different widths at Lowes. I got one that was the correct width (I brought the car with me so to check it). I cut it to the correct length with a metal cutting disk on my radial saw. 

When finished, I connected the car to the engine as a "spacer" car, if you will (It now runs as good as any Athearn). The rest of the train is connected to it. Because it has a truck mounted system, it resolved the "coupler binding" problem I was having. Though the car is now a slightly bit heavier, I usually always run at least two powered engines connected together anyway, so the extra tad of weight is not an issue even for one engine, much less two. 

I now can either pull or push any of the other cars with the SD40-2s, using my spacer car around the 18" radius curves without incident.  The strange part about all of this is that both of the SD40s, while connected together, or when connected to either GP or RS type engines, can go around the 18" radius curves and their couplers never bind against one another. One time I even had an SW1500 connected to one of the SD40s, and they both ran well around the curves together. Go figure.  

Routerman


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## tjcruiser (Jan 10, 2010)

Scott,

I agree with your earlier comment ... I wasn't suggest a full 360 on MDF, but rather just a bit more room for a 270 curve or the like.

I did ask a contractor friend of mine, and he said that he's been able to order oversized plywood in the past.

TJ


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## jzrouterman (Nov 27, 2010)

tjcruiser said:


> Scott,I did ask a contractor friend of mine, and he said that he's been able to order oversized plywood in the past.
> 
> TJ


I agree. Back when I was in the sign business, we were able to "special order" oversized sheets of plywood. 

Routerman


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## Massey (Apr 16, 2011)

Make sure that the couplers can move back and forth freely on the engine. It is really easy to get the screw too tight and the couplers will not move properly. 

Massey


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## mr_x_ite_ment (Jun 22, 2009)

I agree with all advice given on this thread. I don't think anyone can ever go wrong with a larger radius. In my opinion, a radius can never be too big, but we all know it can be too small. In short, I would go with the biggest radius I can squeeze out of it (even if I had to add to a 4 X 8 sheet to get it). I don't have any knowledge pertaining to a helix. I don't know if the helix could be 22" R while all other radii are 24"? Of course, it wouldn't be good if you are pulling cars off the track in the helix either.

Routerman has quite the idea of a spacer car. I learn something new every day! 

Chad


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## mr_x_ite_ment (Jun 22, 2009)

Massey brings up a good point about free play in the couplers. I would check that the trucks turn freely also. I once had some longer well cars with long bars connecting a set of three together. They would derail at the end of a 22" R. I switched the bars for some short shank couplers, and no more problems.

Chad


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## Massey (Apr 16, 2011)

Come to think of it your long shank couplers may be the cause. IF you take a look at it they may swing farther but the angle will be more shallow than a short coupler. Maybe try shorter couplers and see if that helps. I have SD40-2s from 3 different makes, they all have shorty couplers and they all handle 18" radii.

Massey


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## Smokinapankake (Sep 8, 2011)

Thanks for the advice fellas, I'll do some more research. I will say that none of my couplers are binding as they don't use screws to mount; they just fit inside the stock Athearn clips and have all had heights set using a Kadee coupler height gage. Trucks on the rolling stock are mounted with screws so that might be causing some problems being a tad too tight. 

Mebbe I'll fiddle around with some short shank couplers and see how it goes.


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## sstlaure (Oct 12, 2010)

The problem with tight radius inside a helix (at least a round one) is that of grade. I worked out a spreadsheet to calculate grade based on various radii. You also have to remember that this grade will be pulled in a curve making it more difficult.

For a contant circle helix with 4" spacing layer to layer (the minimum you would want to do to give proper clearance for the largest height cars.)

Radius/Linear Run/Grade
20 / 125.7" / 3.2%
22 / 138.2" / 2.9%
24 / 150.8" / 2.65%
26 / 163.4" / 2.45%
28 / 175.9" / 2.3%
30 / 188.5" / 2.1%


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## cv_acr (Oct 28, 2011)

Why are you guys even considering cutting an entire 360deg circle out of a single sheet for the helix? That's a massive waste of material since you're cutting the inside of that circle out.
Rather, cut a series of arcs (like 60-90deg) out of a sheet. Join them using lap joints or splice plates. (Splice plates not recommended inside a helix as the separation between levels will have to be that much greater to clear the plates.) The size of the sheet does not need to match the diameter of the helix.

For the record, I would not even think of attempting a 22"R helix. First of all, in order to get enough spacing between levels, the tighter the radius, the less circumference (distance) and therefore a greater grade to reach the desired spacing.
Also, the tighter the curve, the more drag and an increase in the effect of the grade.
With those factors combined, a 22"R helix will be absolutely BRUTAL operationally.

Also one thing to keep in mind if you plan to try to run long trains through tight helices is to make sure all your cars are up to a specific standard, especially regarding free-rolling trucks and car weight. Otherwise the stresses involved _will_ cause "string-line" derailments of too-light cars in the train by pulling them off the tracks into the inside of the curve.
(At my club we operate 40+ car trains through 30"R helices quite reliably every time we operate. Even the 28"R helix will take a 30-40 car train, although at the 40-car max, any cars that are slightly under standard weight will be very sensitive to the dynamics involved.)


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## Smokinapankake (Sep 8, 2011)

My trains would be max. 5 passenger (prolly more like 3 - it is a tourist type line theme) cars in length. I doubt that would cause enough strain to pull off to the inside of even an 18" radius helix. 

However, right of way negotiations are not going well. Mrs. Smokin' just doesn't understand the need for that much space dedicated to playing when it could be much more prudently applied to.... well, anything else. 

So, I may (probably, 99% sure) not have that 21 x 14 space I had hoped for. Which all makes this discussion, as it applies to me anyway, less urgent. There is some good info here for others' use for sure. 

Hey SStLaure, would your helix grade/diameter spreadsheet be easily modifiable to work for N scale? 
I do have some N scale stuff. 
Just a thought....


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## sstlaure (Oct 12, 2010)

My grade chart was based on a 4" climb per level around a 360 degree sweep. It's very easily modified for N. What is your minimum required clearance for N? Keep in mind you want to leave a little finger room for picking up rolling stock if it falls over inside the helix. 

The linear runs listed above would be correct for the corresponding radii, but you just need to divide minimum clearance in a loop by the linear run.

If you assume 2.5" rise per layer for N (Just a guess on my part - Check the NMRA standards)

Radius/Linear Run/Grade
20 / 125.7" / 1.98%
22 / 138.2" / 1.81%
24 / 150.8" / 1.65%
26 / 163.4" / 1.52%
28 / 175.9" / 1.42%
30 / 188.5" / 1.32% 

I went in to my file and figured out that if you wanted a max grade of 2.5% and a rise of 2.5" per layer - you'd need a minimum radius of 16" for N-scale. If you want the file, shoot me a PM with your email address and I'll shoot it over on Monday. You can even make the helix oval shaped (straights between the end corners). It's just an Excel file.


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