Geometry Question

[wawoodman]

Call the line between the two outside Xs, A
Call the distance from that line up, B

Your formula to find the radius is: R = B[sup]2[/sup] + 1/4 (A[sup]2[/sup])
2B

I used that a lot when I was building cabinets with an arched frame at the top.

 

[wawoodman]

Most humble apologies! I made a stupid error.
The CORRECT formula is now posted! :-\

 

[wawoodman]

That's a goodun to know woodman thanks. Man I wish I could grow my beard like that. Every time mine gets over about a 1/2" my wife shaves my head and threatens to shave it off too if I don't trim it back. She's damned lucky shes cute and smart!

Mine's not happy when it gets too shaggy, either. She walks around mumbling about ZZ Top, and mountain men...

And I finally gave up the ponytail too, after 40+ years. It was too thin to be worthwhile, but man, that hurt! I did it for my 60th birthday, because my mom had been hassling me for all those years. And I'm kind of glad I did, and she got to see it, because she passed away a few months later.

 

[HSS]

The barber at basic training asked me if I wanted to keep some of my hair, I told him yes and he said, hold out your hand.

Pat

And that was in May 1969.

 

[marfaguy]

It won't give you the radius but there's a good way to draw the arc.
I learned this from a long experienced carpenter that regularly had to
make plywood forms so the brick masons could construct archways. The radius
could be very long and impractical to "swing" the arc to draw the cut line.

In looking at your representation, think of the first x as A the second x as
b and the last x as c ( reading left to right so a and c are on a horizontal line).
L1 is the distance from a to c (7.75") and L2 is the height from the mid point of
a-c to point b (.5"). Now set another point d that is L2 above c.
so we have:
x(b) x(d)

x(a) x(c)
Stick a pin at a, b and d. Lay a straight edge against a and b. Lay another
straight edge against b and d. Tack them together and mark the intersection
of the edges at b. I've found it's best to use a third board (doesn't need to
be a straight edge) across the first two so you've got a stiff triangle. Place your
pencil/marker at the intersection. It also helps if you cut a small kerf at the intersection
to help hold your pencil point.
Now with the two straight edges held against a and b draw the first half of your arc. Keep the straight edges against the points as you draw.
When you get to b move the straight edges so they are against b and c and complete drawing the arc.