lots of questions on how tight a corner you can bend a sheet of plywood
around. I found this on a boat building web site.
I hope it helps.
Bending Plywood
The following rough guide for the maximum bend in a sheet of dry
plywood comes from "Boatbuilding Manual 3rd edition" by Robt. M.
Steward (1987). The bend is given as the smallest radius of
curvature to which the plywood should bend without deforming. I
developed a formula to answer the question, "I want to bend a
sheet of plywood 3 inches in 6 feet, what's my radius of
curvature?". The formula I came up with is explained following the
guide.
Bending guide - all measurements in inches.
plywood | min across | min with
thickness | grain radius | grain radius
1/4 | 24 | 60
5/16 | 24 | 72
3/8 | 36 | 96
1/2 | 72 | 144
5/8 | 96 | 192
3/4 | 144 | 240
This table won't work with me. It should say "plywood thickness", "min
across grain radius", "min with grain radius" with the figures below each
heading. I used a | to try to split it up into columns.::frustrated:
The table tells us 1/4 inch plywood could bend into a 4 ft circle
across the face grain and a 10 ft circle with the face grain.
The formula for radius of curvature in inches (r") is:
b" l"**2
r" = --- + -----
2 8b"
where b" is the inches depth of the bend and
l" is the inches straight line length of the bend
(not the curved length of the bend)
and "**2" means "squared"
The calculation for the radius of curvature for 3 inches in 6 ft
is as follows:
raduis = 3"/2 + [(6'x12")**2 / 3"x8]
= 6" + [5184 / 24]"
= 222"
what's below is how I got the formula for anyone who wants to
check it out. all it requires is high school geometry and algebra.
------------------------------------------------------------------
1. draw a circle and a chord. draw the radius from the centre of
the cirle through the centre of the chord and a raduis to one end
of the chord. the arc of the chord is the bent plywood. the length
of the chord is "l", the raduis of the circle is "r", and the
length along the radius between the arc and the chord is "b".
2. the raduis to the end of the chord is the hypotenuse of a right
angled triangle whose three sides are of length r, l/2, and r-b.
The Pythagorean theorum says the square of the hypotenuse is equal
to the sum of the other two squares, ie r**2 = (r-b)**2 + (l/2)**2
3. use algebra to rearrange the sums of squares equation.
r**2 = (r-b)(r-b) + (l**2 / 4) , squaring right side
= (r**2 - 2rb + b**2) + (l**2 / 4)
0 = (-2rb + b**2) + (l**2 / 4) , subtracting r**2
2rb = b**/2 + (l**2 / 4) , adding 2rb
r = (b**2)/2b + [(l**2 / 4) / 2b] , dividing by 2b
= b/2 + l**2/8b
r = b/2 + l**2/8b
