Write an article based on this "Start with a small block of soft wood (pine, basswood or balsa) 1" wide by 1" tall, 4" long. Mark on the wood with a pencil the trace lines as shown in the image. Chisel cavities on both sides of the outlined ball. Turn the block over and repeat. Cut the slivers from the ends of the block. Carefully whittle the slivers from the ball until it can roll freely within the frame."
Notice that the circle overlaps the edge lines a little.  What you're doing is chiseling from the outside in until you have only a sliver remaining in the center, as shown.    {"smallUrl":"https:\/\/www.wikihow.com\/images\/thumb\/5\/55\/Whittle-a-Ball-in-a-Cage-Step-4Bullet1.jpg\/v4-460px-Whittle-a-Ball-in-a-Cage-Step-4Bullet1.jpg","bigUrl":"\/images\/thumb\/5\/55\/Whittle-a-Ball-in-a-Cage-Step-4Bullet1.jpg\/aid42434-v4-728px-Whittle-a-Ball-in-a-Cage-Step-4Bullet1.jpg","smallWidth":460,"smallHeight":325,"bigWidth":"728","bigHeight":"514","licensing":"<div class=\"mw-parser-output\"><p>License: <a rel=\"nofollow\" class=\"external text\" href=\"https:\/\/creativecommons.org\/licenses\/by-nc-sa\/3.0\/\">Creative Commons<\/a><br>\n<\/p><p><br \/>\n<\/p><\/div>"}