[TheForge] Forge Geometry- calculating a radius

[Steve Smith]

Kirsten, the formula looks to be correct, but I'm worried about an 
assumption. How do you know that the railing is circular? Could it be 
elliptical, or whatever came out of the shop that day?

One way to find out would be to check small segments of the railing for 
radius. All you want to know is if the radius is the same, so make a 
template with the radius you measure (maybe a foot or two long) and 
slide it along the railing. It should be pretty obvious if one section 
has a different radius.

Steve

Fiorini & Skiles wrote:
> I was trying to figure out how to accurately measure an existing radius 
> for a curved railing. I came across this formula from 
> http://www.johncglennon.com/papers.cfm?PaperID=17
> 
> R = Lsquared /8m + m/2
> 
> Where
> 
> R = the roadway curve radius, feet
> 
> L = the chord length, feet
> 
> m = the measured middle offset, feet
> 
> This particular website was actually demonstrating another method that 
> was more appropriate for road work. But the formula above seemed like it 
> would be fine for the curve I'm dealing with.
> 
> Does this work accurately for a railing curve, when you've got the curve 
> all laid out, easy enough to measure? It gave a close, but about 3 inch 
> different number than our rather inaccurate 
> 2-people-pretending-to-be-a-compass method. I'm planning to go by the 
> mathematically calculated number.
> 
> Is there a better way? Will that geometry give me an accurate result? 
> Are there any other good websites or books on construction geometry?
> Thanks,
> -Kirsten
> www.knitsteel.etsy.com
> 
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