Diameter of an HO curve

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AllenB

Member
If I have a line going north, then a turn to come back south (parallel),...what is the diameter of the turn? I'll be using flex track, but don't want to make it so tight that I can't run longer cars. I'm trying to figure out how wide my benchwork is going to be (I'm making a rough draft on graphing paper first).

Thanks!
Allen
 
Wow, that's one vague question.

Are you asking what the smallest turn HO equipment can make is? Even that is a rather broad question that has been answered many times.

I think we need more info from you :)
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PornCollegeGirl
 
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LoudMusic said:
Wow, that's one vague question.

Are you asking what the smallest turn HO equipment can make is? Even that is a rather broad question that has been answered many times.

I think we need more info from you :)
Click to expand...

When I graph out my benchwork, I'm trying to figure out how wide it'll need to be. The shorter the better. If I can get a turn in within 3 feet of space Diameter)...that'd be great (my layout would be a rectangle 14 feet long by ? wide). But if the turn is going to be too tight, I may have to extend it to 3.5 feet but I'm not quite sure. I'd like to run two lines side by side. I don't want to go too tight though. Make sense?
 


I use 22" as my minimum radius on the bracnh line. THis means the total turn has a diameter of 44". So, your benchwork I guess would have to be 44" wide. Problem with narrow radius turns is the type of equipment you would like to run. So, you have to figure out what your goals are for the layout. Do you want to run 40' boxcars, or long passenger cars. The longer the car the wider the turns are gonna need to be.

Sounds like 3' is pretty tight. If I am doing my numbers right, your max radius would be 18" and that would go right to the edge of the table. That can mean an expensive meeting with gravity. A fight I've never won. Again though, with 18" radius you will be limited on the equipment you are running.

Some of the more experienced heads on here can verify if this is accurate.
 
Too Tight??

Why a rectangle?? Why 3.5 feet?? Why 2 lines side by side?? Why not a dog-bone, big on the ends and narrow in the middle?? Why not around the walls??

18" radius (center to center of track) gives a 36" diameter plus 1" on both sides to edge of roadbed (38" outside to outside) for the outside track. The inner track will have to be at least 2" smaller radius (16") and maybe more in the curves to prevent side-swiping of longer cars. You may have to rule out 3 axle trucks on equipment, full length passenger cars and long steam engines.

With these curves you will be operating at the very edge of the layouts so may lose equipment over the side if derailments happen. Also you will not have any scenery between rails and side.

Most all of us have to give up something to build our layouts, size, money, equipment, time, space, family...take your pick. My full length SP Daylight coaches side-swiped my UP Big Boy on a modular layout with 30" radius.

I presently have a 4'x4' with one circle of 22" radius. Not any operation but will run most of my equipment.

Armchair
 
I'll try and post a picture of my draft. Each square represents 6 inches. So my basic question is is this to scale and realistic to get two trains around the turn. Again, I won't be running any large passenger cars or large steam engines, but I don't want to limit myself to only running shorty tank cars either.

http://s238.photobucket.com/albums/ff35/smawgunner/Train Set/?action=view&current=20101216092217.jpg

http://s238.photobucket.com/albums/ff35/smawgunner/Train Set/?action=view&current=20101216092200.jpg
 
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You have done a reasonable job of sketching an inner curve on that loop about 18" in radius. The diameter of a circle has two radii, so if you have two radii in that almost-circle, you have a diameter of twice 18", or 36". But that's just for the tracks, and your outer track has a diameter closer to 41" if you have spaced them properly so that rolling stock don't interfere with each other on the curve.

Which suggests to me you have a reach problem, and rather severe....if I accept that your benchwork will cover the whole frame you show your loops on.

Crandell
 
Pictures! Those are extremely informative :) Perhaps worth a thousand words.

For the most part I think that's a good looking layout. But I think Selector is right, assuming the lower center portion of the drawing is your operating space, you'll have a hard time reaching the back corners if the layout is surrounded by walls. However, there's not much back there in your drawings so maybe it won't be much of an issue.

I may try to poke this into some layout design software later today to get more exact dimensions for you. But I believe typical reach access is considered to be about 30", or 2.5 feet.
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Side Effects Of Prilosec
 
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LoudMusic said:
Pictures! Those are extremely informative :) Perhaps worth a thousand words.

For the most part I think that's a good looking layout. But I think Selector is right, assuming the lower center portion of the drawing is your operating space, you'll have a hard time reaching the back corners if the layout is surrounded by walls. However, there's not much back there in your drawings so maybe it won't be much of an issue.

I may try to poke this into some layout design software later today to get more exact dimensions for you. But I believe typical reach access is considered to be about 30", or 2.5 feet.
Click to expand...

If the reach turns out to be a major issue, I can design it where the rear of the benchwork actually touches the wall and the sides do not. But we'll see.
 
My first pass was to simply put your drawing into XTRK. I think you've got a great foundation for a layout.

allenb.jpg


Obvious design problems I see:

>> The circles are 30" radius, representing operator's reach. There is quite a bit of inaccessible layout in the corners. Not a problem if your trackwork is amazing, but lets face it, no one's is. I'd either limit track in that area to main line with no switches, or figure out how to get access to it easily. A step stool will only add so much reach, and even then you'll be climbing on the layout.

>> The crossover at the back of the layout needs to be on the other side of the yard lead so that the yard tracks can be another 9" longer.

>> I used 2" track-to-track centers spacing per this 'standards' document. http://urbaneagle.com/data/RRstddims.html It actually suggests 3" centers on curves which I did not do, but probably should be done.

>> The same standards page lists railhead-to-railhead clearance at 4" vertically. Assuming all your track is at the same elevation except the part that does the bridge, you don't have near enough room to get up and over the other piece of track with reasonable grades ( ascents / descents ). Typical acceptible grade on a small layout is 3% (raise 3 inches per 100 inches of travel). One side of this bridge is 9.2%, the other is 3.5%. I have ideas for adjusting this.

>> Most importantly of all, however, is that all your industry leads are on the far side of the layout. If you're operating turnouts manually you'll get tired of that real quick. If you're automating it gets expensive and complicated real quick. And furthermore, this is the interesting stuff to play with. It should be up close where you can mess with it. Also, if it fails, it's a pain to get to.

>> You don't have a way to turn an engine around. Reversing wye, reversing loop, turntable ... they're more trouble to wire, but often times are very handy to have on a layout.


Depending on how much you're willing to change, I think you could have a really fun layout in your space. I can provide you with the file I created for this layout, but you're on your own to find help learning to use XTRKCad.
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Lovely Wendie99
 
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By the way the radius is measured to the center of the track. You would need more than 44 inches for a 22r curve. Diameter is simply 2x radius.
 
hamltnblue said:
By the way the radius is measured to the center of the track. You would need more than 44 inches for a 22r curve. Diameter is simply 2x radius.
Click to expand...

Correct - typically an HO track needs 2" of width, so (radius+1)x2 is your absolute minimum benchwork width.
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SUBARU BRAT
 
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