I have the generic benroy plans, and I have a ??? Im not quite sure about the radius figures on page 17 of the plans. I built my home and I have a daughter with a masters in math. but we cant figure this out. The front upper curve is a 19 radius, meaning to measure down and across 19 inches giving you your radius. Now to the hatch end,it says a 48 inch radius but they only measure across 41 9/16 so how can this be? I hope its just an oversight on my part, I would appreciate any help. Thanks
I don't know the technical jargon, but the back radius is not equal on the corner. If you moved the mark up 48" instead of the 41 9/16 as is recommended, you would not have the rear "flat" section, the entire back would be one big rounded piece.
I shortened the rear top radius to 47" so my router jig would sit ON the side rather than 1/2 off. I retained the 41.563" dimension but rounded it off to 41.0" . The dowel in the center of the 2x2 was at the junction of the 47" and 41.5" when the arc was cut.
Back when I was working on submarines, a machinist boss came to me with a couple of his workers in tow and was trying to calculate the area of a circle. He refused to accept that the area of a circle is Pi x radius^2 (pi r squared), instead thinking that it was Pi x diameter. I was gentle with him, being younger at the time and not wanting to embarrass him in front of his guys (who were clueless to the math). Later he came around to my way of thinking and from that day on all of the machinist on the site started calling me by my new nick name "Piard" (from Pie-are-d).
I really liked the Benroy radius but I imagined having to repeat that radius with a router multiple times and sort of chickened out and just did a three foot radius in the back and an 18 inch radius in the front. Looks simple but not unpleasing to my eye. The Benroy actually gives you MORE vertical height on the back hatch before the radius begins.
Just as an "aside" (not addressing the technical part of your question) I had cut my pattern out with the 19" radius, and to my eye it seemed a little too severe a curve, so I recut it with a 24" radius and really love the lines of it now.