Carving a round ball from a square piece of wood is a great way to learn and/or practice knife skills. Carving a Ball is also a good way to practice several knife cuts.
Several years ago, while participating in a woodcarving show I watched a very experienced carver whittle such balls from square stock. I asked him, "why the balls"? His reply was, "I've been carving for 30 years, but never got too old not to practice.
I'm old now and understand the wisdom of that answer.
I use this exercise when instructing new carvers. I find it a great way to practice thumb assisted push cuts and paring cuts.
STEP 1: Ware a cut resistant glove on your hand that holds the wood. Ware a thumb protector on your hand that holds the knife.
STEP 2: In the photo I use a 3/4 x 3/4 x 4 inch piece of Basswood. 1 x 1 x 4 inch would also work. The extra length of the wood serves as a handle and for carving additional balls.
Draw a pencil line around the top of the piece of wood 7/8 inch from the end.
STEP 3: Using a thumb assisted push cut remove the corners of the wood at the top of the piece.
STEP 4: Remove the bottom corners of the wood using a thumb stopped paring cut.
STEP 5: Use a combination of the thumb assisted push cut and thumb stopped paring cuts all around the piece until all the flat wood is removed, and the ball shape is achieved.
The key to this project is practicing the knife cuts. Do not attempt to remove too much or too large a chip with these knife cuts. A great wood carving friend told me to "think grains of rice".
STEP 6: Here's one completed ball.