Trainlover160 posted:

Hi Chris, I thought it was marked underneath the roadbed like Fastrak

Joe Gozzo

Hi Joe. I wanted to avoid pulling up the track pieces if I could help it. GRJ suggestion is good but it might be easier for me to pull the track!   John gives me way more credit than I deserve! 😂




Home of the C.L.&M railroad






Not to belabor this or embarrass my high school geometry teacher, but in my world diameter is defined as the straight line through the center of a full circle so, by definition, a semi-circle cannot have a diameter. The straight edge of a semi-circle is simply the diameter of the full circle from which it came but it cannot, itself, have a diameter.  

That's my story and …….


Jon1443 posted:

If you want to get really fancy and mathematical, you could measure the arc length

Sure, just show us how simple that would be.

How to Determine the Length of an Arc

I think I'd just put the track together and measure the radius.

Boy this sounds like beating a dead horse.     Simply measure across the half circle with a yard stick in inches, and then divide the result in half (ie by 2).    If  you come up with 36, your raidus is 18, if you come up with 30, your radius is 15.     It is not necessary to take the track  up, why make work?

18" used to be the basic size used for HO in starter sets and the like, but that was before EZ-Track. 

I recall using some 15" on my layout as a kid, and it was tight for most equipment, aside from short freight cars.

I guess maybe they changed since Chris measured 15".


PLCProf posted:


All you need is 1 piece of curved track and a straightedge and a ruler as shown in the photo. Radius of this piece is about 18, it is O-36. 

No good - Too simple.......

Not that I am disagreeing, but you have to admit for the general trig class they don't assume the width of the line defining the circle would be wide enough to know which direction to point the ruler and straight edge to end up in the center.

Without the width of the track to guide us in how to hold the ruler roughly perpendicular at the ends of the piece of track, it would be easy to measure incorrectly with that method.


Well, since we're not in trig class, and he's using track with a plastic roadbed, the simple method works just fine.  I didn't even think of that, but it's simple as you don't even have to plug several pieces together to make the measurement.

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