Track diameters and clearance

Just to be clear, these are diameters.  So if you use 0-81 and 0-72 together the difference is 9" total so on each side to the circle you will have 4 1/2" center to center. 

I am sorry, I meant to say 4.5 inch centers. The overall diameter difference between the O-63, O-72 and O81 would be 9 inches each. I am trying to avoid placing straights in the radius if possible, so that the curves remain smooth and consistent.  I was afraid the O-63 might be a little sharp and create too much overhang for traffic on the O-72.  Sorry about the confusion .

What size Madison cars and what type of scale steam are you running. If you are running  Articulated steamers like Big Boy and Allegheny as well as 21" passenger cars you  can run them on 072 and 081, HOWEVER you will have some over hang and two trains on your curves at the same time will likely clip each other. If you use smaller steamers like consolidations and K4's with 18' and smaller cars you should be ok.  If you opt for the bigger cars and engines you couls do as I have done on my layout. 

1. Lay down the 081 curves.

2. Start the 072 curves 4-5" sooner than the )81

3. Likewise start the 063 4-5" sooner than the 072. this will give you a bit more clearance.

Hope this helps

SCALE passengers cars of the 18" or 21" will be close with the overhang on the O72 out to the O81. I think that they would definitely hit on the O63 out to the O72.

Most SCALE steamers will be ok. The articulated engines will not.

All of the semi-scale equipment will work.

I would suggest staggering the entry point to achieve 5.5" centers in the curves. Start with the outside line where you want it. Then, set the inside line at 5.5 for the O72. Ovals would be simple. Making reverse turns would cause you to mix in other diameters.

The simple semi-circles would look like this - 5.5" at the apex to start - work away from there - Do the same of the other end - then cut some straights to fit the two.

Carl, I must be missing something. The double O72 crossovers at the top and bottom have 5.5" centers. The rectangles at the apex are 5.5" wide.  I don't believe there is any way to maintain 5.5" centers throughout the curve without adding straights at the apex.

@DoubleDAZ i don't mean to criticize.  But you shouldn't be using O72 "switches" (with a curved leg) for the crossovers.  The Ross standard switch (which is a cutdown #5) or a #6 would be a better choice for a crossover between mainlines, and I believe it can be integrated to parallel mainlines with 4.5" track centers.  Another tip: avoid butting the switches right up against the curves as in your graphic above because this creates an "S" curve through the curved path of the switch.  This should be avoided if possible.

One solution might be to acquire a few Ross standard switches (product no. 100 or 101) for the crossover between mainlines, and use your K-Line track for everything else.  I don't have stock in Ross or anything, but I've used their track myself and it's a great product.  The variety and selection they have offer possibilities that, frankly, most other track systems can't match!

Ted, criticize all you want, just know what you're criticizing.

In this case, the crossovers are just to show the spacing, they have nothing to do with any suggested use for an actual layout. They happen to result in 5.5" centers and simply illustrate how the concentric circles will not remain at 5.5" without adding some straight spacers. When I want to maintain a certain spacing around a layout during the design phase, I often place crossovers with that spacing in key locations and then replace them with straights once the design is far enough along. That's much easier that constantly measuring the spacing to make sure there's enough clearance.

Wait a minute. Something is wrong with Carl's diagram. If each concentric circle has the same number of pieces, then the end of the 90 degree  arcs MUST match! In the diagram, they do not. The 9 o'clock positions align, but the 6 and 12 o'clock positions do not. Which means the 5.5" spacing cannot be with the diameters of track sections selected. One can move the individual circles until the 90 degree positions align, which will insure the circles are concentric, but then the spacing will not be as desired.

Chris

LVHR

Keith,

Take a few minutes and actually lay your tracks out on the floor.  Build your concentric circles, then measure the real distance between track centers. I think you will find there are differences in how companies measure/report curve diameters.

BTW, the larger the diameter of the circle, the less overhang you will incur on both sides of the track, which means the larger circles can be spaced closer together.

Chris

LVHR

DoubleDAZ posted:

Carl, I must be missing something. The double O72 crossovers at the top and bottom have 5.5" centers. The rectangles at the apex are 5.5" wide.  I don't believe there is any way to maintain 5.5" centers throughout the curve without adding straights at the apex.

 

Dave, yes, I am aware that the center rail spacing gets closer on the straights. 4.5" is ok on straights. I didn't really measure. The goal was to provide ample clearance in the curves to deal with overhang of 18" - 21" passenger cars. An articulated engine should be on the outermost track.

I wouldn't call them concentric semi-circles because they don't start and end at the same point or technically, they do not have the same center point of the circle.

lehighline posted:

Keith,

Take a few minutes and actually lay your tracks out on the floor.  Build your concentric circles, then measure the real distance between track centers. I think you will find there are differences in how companies measure/report curve diameters.

BTW, the larger the diameter of the circle, the less overhang you will incur on both sides of the track, which means the larger circles can be spaced closer together.

Chris

LVHR

Chris,

I had to use RR-Track for the K-line library. I am not really concerned how they set the track at the factory, I created the desired spacing by starting at the apex.

I would assume that the "diameter of circle convention" was used. Any rail would be smaller, since the outside tie end makes the circle.

lehighline posted:

Wait a minute. Something is wrong with Carl's diagram. If each concentric circle has the same number of pieces, then the end of the 90 degree  arcs MUST match! In the diagram, they do not. The 9 o'clock positions align, but the 6 and 12 o'clock positions do not. Which means the 5.5" spacing cannot be with the diameters of track sections selected. One can move the individual circles until the 90 degree positions align, which will insure the circles are concentric, but then the spacing will not be as desired.

Chris

LVHR

Chris,

Not concentric. yes, the 12 and 6 o'clock positions do get closer. it's ok because the trucks are not turned a lot and there would not be much overhang. Staggering the ends is how to achieve the center rail spacing in the curves.

5.5" inch spacing is not needed on the straights.

C'mon guys, take the track that he has and make clearance for scale equipment with 3 lines.

Keith, as you said, concentric circles have 4.5" centers. It's true that manufacturers differ, some use outside rail (K-Line I believe) and some use center rail (Atlas I believe), but the center-to-center spacing doesn't vary for a given manufacturer, only the size of the circles vary and in this case, Atlas circles would be slightly larger.

It's also true that larger curves mean less overhang. However, the half-circles won't be concentric if you vary the spacing. The only way to maintain concentric circles is to use 4.5" centers and, as Carl said, I think you'll run into trouble doing that. IMHO, the small fillers needed for the 5.5" spacing won't be noticeable after all is said and done. YMMV

Carl, he said he wanted concentric arcs without using spacers and there's simply no way to do that. I completely agree that your diagram will work, but that's not what he asked for, hence the discussion.

DoubleDAZ posted:

Carl, he said he wanted concentric arcs without using spacers and there's simply no way to do that. I completely agree that your diagram will work, but that's not what he asked for, hence the discussion.

Correct - and you and others have demonstrated that that is not possible by definition of concentric and the geometry of the track. Therefore, I provided a solution.

What is said is correct, you can not run a scale Big Boy on the O72 track and not hit scale 21" passenger cars on the O81 track with 4.5" track spacing.  5.5" spacing on curves in the minimum, this is why Lionel's FasTrack is set at 6" spacing.  Past forum member Lee Willis provided a nice set of photos showing this.  If you want 5.5" spacing on your curves you have you will need to follow either Carl's or Dave's suggestion.

Wow, now I see that Carl and Dave are right.  I never thought it out.  Yes, Lee Willis would have certainly done a monumental job in documenting something like this.  Thank you everyone for the education!  

I would like to thank everyone for their replies. The passenger cars that I have are postwar style Madison and prewar tin, so nothing very long.  The engines are scale mikes, hudsons and prewar tin.  If I were to purchase an articulated engine and run on the outside loop, but run with the shorter cars would I still have problems with clearance on the O-72 loop ?  Thanks again to every one that posted, and I might consider pulling the loops forward if I have to, but if the concensous is that I will be okay than I will leave well enough alone.    I was going to assemble the track on the floor but none of it has ever been used and I thought that putting together and taking apart might loosen the fit so I decided not to. 

I recommend 6" spacing, our club layout has 5.5" spacing on some O90 and O81 adjacent tracks, and I managed to clip one of the 85" boxcars with my VL-GG on the turn. 

FWIW, here's 6" spacing with 3 1/4" and 6 1/2" fillers.

I am going to go with the 6 inch spacing. Dave's diagram shows that it really won't be that noticeable that the circles are not concentric and I don't have to worry about side swiping anything. This will require a little more real estate, but worth the peace of mind. The O gauge forum is a treasure trove of information, thanks to people like you who have responded to my question.