gregc Others can provide more experienced suggestions for how long a straight section is needed.
The length should be equal to or greater than the longest wheelbase on your rolling stock or locomotive (e.g., a SD-60 class is about 8.2 in). So if that is the longest wheelbase, a 9 inch straight section would be OK. In planning the CT River Valley RR, I maintain at least 12 inches between the reverse curves, except within yards.
Co-owner of the proposed CT River Valley RR (HO scale) http://home.comcast.net/~docinct/CTRiverValleyRR/
TrainsRMe1I want to build a return loop, ... ...where do I start measuering to get the right demensions I need. for a good loop, I guess I need step by step instructions on how to do this.
...where do I start measuering to get the right demensions I need. for a good loop, I guess I need step by step instructions on how to do this.
the figure shows a minimal size reversing loop. It is 3/4 of one circle and 1/4 of a 2nd circle. The diagram shows the centers of both circles used to draw the circles drawn with either a string or yardstick as described in previous posts. The centers of each circle are 2xRadius or Diameter apart and parallel and Radius from the straight length. Other responses have indicated minimum Radius.
I hope that it is clear (you asked for step by step) that these centers are a bit more than Radius from any wall or layout edge. If a layout corner were at the bottom right corner, and the tracks 2" from the edge then the right had center will be Radius + 2" from both edges at the bottom and right sides of the figure. The left hand center will then be Diameter further to the left, Diameter + Radius + 2" from the right edge and Radius + 2" from the bottom edge.
As others can explain better, there is a potential problem where the curves reverse between the two centers. This can improved by increasing the distance between the 2 centers and drawing a tangent to both circles. This of course increases the horizontal dimension of the reverse loop. Others can provide more experienced suggestions for how long a straight section is needed.
greg - Philadelphia & Reading / Reading
Start with a full circle tucked into wherever the loop is to be. image 1Take a two tangents to the circle, remove the circle track between, and put straight track there. image 2. Here ideally one would want the angle of the two tracks to equal the angle of departure of the turnout being used to make the loop.Join the two tanget tracks with a turnout.
Note that one can greatly reduce the length of a reversing loop by making the main circle longer and putting a reverse curve into one of the legs rather than forcing it to be a true tangent straight line. In image 3, I made the circle 30 degrees longer than image 2. After some straight track (needed to avoid S-curves), I curved the track 30 degrees back the other dirction.
This quote is from the earlier post (link posted above).
selector TrainsRMe1: ...with the string and pencil, would I start the radii mark from a middle pivot point?? Thanks again for the Help!!!! Yes, exactly. You have to fiddle with a pivot point inside the curve you desire so that you get the radius you desire WHERE YOU WANT the curve.
TrainsRMe1: ...with the string and pencil, would I start the radii mark from a middle pivot point?? Thanks again for the Help!!!!
...with the string and pencil, would I start the radii mark from a middle pivot point?? Thanks again for the Help!!!!
Yes, exactly. You have to fiddle with a pivot point inside the curve you desire so that you get the radius you desire WHERE YOU WANT the curve.
Rather than fiddling with the pivot point, simply use a yardstick or similar device to draw a suitably-sized circle on cardboard (a flattened carton from the supermarket, perhaps), then cut it out using a knife or scissors. Place it on the layout and move it around until the curved portion which you require is at the spot where you want it to be. If your cardboard was cut-out accurately, simply trace around it with a pencil. Otherwise, use a pencil to poke through the centre-point of the cardboard, and make a mark on the layout. Use this mark as your centre-point for drawing the curve directly on the layout, again using the yardstick.
I made a couple of radius trammels for building my HO layout, using strips of 1/2" plywood. One is for radii 18"-34", while the other is used for 22"-48".
I used a tape measure to mark it off in 2" increments, then drilled appropriately-sized holes for a pencil:
The pivot end was drilled with two holes suitable for a 2" nail, and marked as shown.
These were used to draw radii on 3/4" plywood sheets, then the curved sections were cut-out using a jigsaw, and spliced together lengthwise. I simply set them atop the open grid benchwork, choosing the largest which would fit in each location where a curve was required.
Wayne
Byron has provided you with an excellent response. As we attempted to make clear earlier, a radius is what you use around a central pivot point to creat a full circle, but you have to sweep it sideways a full 360 degrees to create a full circle. A curve on a railroad is virtually never going to create a full circle, but it does place a portion of a circle on the ground. In fact, railroads are really tangent lengths of track (straight tracks) that serve to join all the myriads of curves here and there scattered across the landscape so that railroads can maintain the easiest grades and get around obstacles. Not entire circles of track, just a curve, a portion of a circle. But that curve has a central pivot point for its radius, just as a full circle has, as Byron's diagramme depicts.
For your scale, 12" is about as tight as you would want to impose on your locomotives, particularly when you ask them to tow their trains behind them up a ramp such as on a grade or around a spiral helix to gain altitude. The curves act like a grade, and when you throw a grade in on top of the curve, or vice versa, you compound the load for the locomotive. If you can widen any curve on your layout, you reduce both the load and the likelihood of derailments due to flanges climbing out of the rails when they encounterr irregularities in rail height or a sustained curve. The tighter your curves, the higher the probability, statistically, that your track irregularites will cause derailments. On hidden tracks, such as in a tunnel or a helix, those can effectively kill all enjoyment in the weeks and months ahead. Best to deal with the probability of unreliable tracking during the planning process, not the taking-everything-apart-to-start-over process.
Crandell
TrainsRMe1I'm running modern era,loco's (six wheeled locos) I understand that it's best to build a loop at best 12 inches across, as I think of it I would like to add storage tracks either inside the loop or outside,
"12 inches across" suggests diameter. That would be roughly 6" radius, not sufficient for the models you have in N scale.
Model railroad curves (except for 3-rail O Gauge) are typically measured in radius to the center line of the track, not diameter.
So the first step might be to be sure that you are planning for 12" radius.
As far as the process, you received pretty good advice on how to lay out the curves in an earlier thread. So maybe you could let folks know what additional information you need that wasn't covered in that thread:http://cs.trains.com/TRCCS/forums/t/188619.aspx
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K MRRDERS, Im back again and I want to thank you guys for helping me out, however, I seemed to have not caught on, To make it clear on what I"m asking, first of all I'm working in Nscale, I want to build a return loop,on one end of my layout, now I'm running modern era,loco's (six wheeled locos) I understand that it's best to build a loop at best 12 inches across, as I think of it I would like to add storage tracks either inside the loop or outside, Okay guys -n- gals that's where I'm still stuck, where do I start measuering to get the right demensions I need. for a good loop, I guess I need step by step instructions on how to do this.
Thanks for all the help, and I hope I'll catch on this time.
Trainsrme1