Been a loooong time since math in school, and a little embarassed to have to
ask this. If I have a hole I want to line with felt, what is the formula
for figuring the length of felt to cut? Thanks guys.
If you remember that there are 2*Pi radians in a circle,
it also gives you C=2(Pi)r, or C=(Pi)d.
If you've had calculus, thinking of the area of the circle as the
collection of "skins" having thickness dr, you can integrate C dr over
the interval [0,R] to get A=Pi R^2. At least, that's one way. I just
mention this for the readers that are math fans.
A poor farmer worked long and hard to send his eldest son to college. He
looked forward to saying with pride that the family finally had their
first college graduate. Son grew up, went off to college. His father
continued working hard to pay the tuition.
Four years later, son came home with a diploma. Excited to know what the
son had learned, his father asked him to tell him something.
Son replied "Pi r2," which the father heard as "pie are squared."
Shocked and angered, the poor old father tore his straw hat off his head
in disgust, threw it onto the ground and yelled at his son: "You
dingbat! Pie are ROUND...cornbread are square!"
Felt has thickness, so technically, the calc of the hole won't be correck,
altho the diff could be negligible.
Another way to get a perfect fit with no calc at all is to cut it a bit
long, wrap it on the hole, and just cut the overlap (winding up with two
drops), for a perfect fit.
Well technically the thickness of the felt has noting to do with the
calculation. He wants to line the hole with felt. That distance is
what you will need to use to cut the felt. If he cuts the felt longer
than the perimeter of the hole it will not lay flat. If he cuts the
felt shorter than the perimeter of the hole it will be too short. The
only length that is important is the surface. Felt thickness will compress.
Yeah, but if you cut it long, and then razor it as it lines the hole, the
fit will be exact -- incl. the angle of the "wall" of the felt, if it were
substantial, would also be angularly correct! You could actually glue the
overly-long felt in the hole, making the cut very easy to coordinate.
Also, the cut doesn't have to be at all straight, bec the ends of the felt
are overlapping, and will match no matter how sloppy the cut -- as long as
the cutting knife catches both overlapped pieces. In fact, one could arger
against a perfectly straight cut, and could even do a kind of "toilet roll
tube spiral" -- depending on what's going in the hole, etc.
For one-offs, this cut'n'match is proly the preferred way. It of course
would not be efficient for production jobs.
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