Question about kerfing mdf

[J_DOG_LOZANO]

Ok so i already watched marks video on how to kerf, i got most of it down. The part im stuck on is like when he said "find the diameter of the curve" what does that mean? How do i find the diameter?

[john253a]

So the dia is if you have a prefect circle measure across it and that's the dia

The circumference is the dia X pie ( or 22/7 )

So say you want

r3" bend

That means the kerf is 3" deep and 3" wide on the box

So it is a 6" dia witch is 18.85" circumference

Then you devise 18.85 by 4

As you are only doing a 1/4 of the circle

So you need 4.71" of mdf