N-Scale Curve Radius - Inner Rail, Outer Rail, or Centered?

[baumgrenze]

I have an digital image of a setup I built for my son in 1973. I've pasted it into Autosketch 9 and approximately adjusted it to scale. I want to be able to measure and describe track lengths and curve radii.The maximum elevation change on the viaduct is 1.75". I long ago lost the parts list. I'm pretty confident it was all Atlas. This was prior to DCC so it was built in 5 insulated sections, each controlled by a DPDT switch so directions could be reversed section by section. It took a fair amount of attention to run a train on it.

Do I sketch in the lines approximately halfway between the tracks? I want to be able to describe the curve radii.

Thanks

baumgrenze

[Attuvian]

Welcome to the forums, friend (at least as a poster). 

In all scales, radii are measured to the center, mid-way between the rails.

 

John

[Tinplate Toddler]

Just to make your picture visible in this thread:

Attuvian

In all scales, radii are measured to the center, mid-way between the rails

I´ll second that!

[baumgrenze]

Thank you both for your informative replies.

As time permits I will work with AutoSketch and get a better description.

baumgrenze

[baumgrenze]

I made some progress today.

 

The track appears to be Atlas Code 80. The ties are black. Some is Snap-Track with the joiners and some is not but it all looks line the same track. When did Atlas introduce this 'feature.'

 

I used a dressmakers tape and also a 6" flexible plastic rule to measure the track sections. I found that the curved sections are 4" and 5" long. Is this a function of the radius? I found the current Atlas catalog and see that Code 80 track comes with 3 standard radii, 9.75", 11", and 19" and in 'full size' and 'half-size' but I found no track lengths. Is there a table of curved track lengths on the web somewhere?

 

The outer loop along the right side of the image is 2 full lengths of Flex-Track and a 10.5" added section.

 

I opened my image of the layout in Autosketch and adjusted the dimensions so that a 5" line matched a 5" length of straight track and checked that the side to length ratio of the rectangle was accurate. I drew in 'centered' lines along the track and marked all the junctions I found. Drawing 3-point curves with Autosketch is an iffy proposition and when I check Entity Properties I find the drawn radii as small as ~8". I could take closer photos of track sections and do a better job, seeing if I could get a circle segment to work as a centerline, then trim it to length and get at the radius that way. It is hard working backwards.

 

My first approximation for the grade on the viaduct loop is a 49.25" track length over a 1.75" rise and a 48.125" track length over a 1.75" rise. If this ratio is the grade, I come up with 3.55° to 3.65° because the lengths are slightly different.

 

I hope some reader knows about the curved track lengths.

 

thanks

baumgrenze

[Tinplate Toddler]

Hi Baumgrenze!

I think youn are putting way too much effort into recreating the track plan. I think there is an easier way to do that than with the tools you are using.

There is a free track planning system called SCARM, which has a Atlas N scale code 80 track library incorporated. The software is easy to use and should enable you to recreate the plan within a couple of hours.

A click on the name will link you to the download page.

 

[BigDaddy]

I think flex track would eliminate a lot of the angst you are having about how long each piece of track needs to be. 

As our skills, knowledge and experience change in the course of our life in the hobby we find ways to improve our layouts. 

Very few of us have built that same layout, twice.  Are you building this for a grandchild?  Is there nothing you would change about it?

You didn't ask, but there is a reversing loop in there.  Was the S curve at the top turnout a problem?

[baumgrenze]

I see I failed to state my goal clearly.

I want to accurately describe an existing layout so that I can find it a good home.

At 78, my vision is failing and it is time to downsize.

The child I built this for is now 50; he has no interest in it.

I hope this explains my request for information.

Thanks for participating.

baumgrenze

 

[baumgrenze]

I figured out how to get the information I wanted. The math is stuff from high school (1954-58.) I measured the track lengths at either 4" (tightest curve, 9.75" radius) or 5" for the 11" and 19" radius. The central angle in radians is the curve length divided by the radius. There are ~57.3 degrees/radian. It is easy to draw the circles in a drafting program and to cut the desired arcs. If you center the circles (draw the smallest and then draw offset circles using the differences in radius) you get 3 concentric circles. You drop a perpendicular down through the center and draw angles from the center point. In my program I needed to use half the calculated central angle and draw it from the center to both sides of the perpendicular. I can post an image if anyone wants to see it.

Here is the information in tabular form:

arc (s) "	radius "	θ = s/r (radians)	in degrees
4	9.75	0.41025641	23.50596923	smallest radius
5	11	0.454545455	26.04354545	medium radius
5	19	0.263157895	15.07784211	largest radius

 

Thanks for your interest and support.

baumgrenze

 

[BigDaddy]

baumgrenze

I want to accurately describe an existing layout so that I can find it a good home. At 78, my vision is failing and it is time to downsize.

Didn't see that coming.  I could use some of your down sizing energy.

Vision problems are more common as we get older.  Some respond, in fact require treatment.  Don't short change yourself by not seeing an eye doctor.

Best of luck.

[Tinplate Toddler]

baumgrenze - I don´t want to rain on your parade, but used layouts have a very limitred market value, if any. Even highly scenicked and detailed layouts sell for very little money. Most of them are salvaged for parts with the remains ending up in the dumpster.

The most important information when attempting to sell a layout is the overall size, followed by the number of switches and an approximation of the total track lenght. Not to forget the scale, the brand and trhe number of locos and cars to go with the layout.

Good luck!