So, a while ago I was talking with some fellow knitters and wondering why people would pay to have their yarn balled for them at the yarn store, when it is so easy to re-ball it yourself. They answered that it was the only way to get balls that unwind from the inside, so they don’t roll all over the floor as you work and tempt the cats. Not true! It’s easy to do at home with no or minimal tools.
Note: yarn tension may be a valid reason to prefer store-winding; in general, balled yarn will be under tension and may stretch out over time, and hand-winding may result in more tension, so hold the yarn as loosely as you can while still controlling it.
1: Without tools: with your off hand, take one end of your yarn and hold it with your thumb against the base of your first two fingers. Start wrapping the yarn around the tips of these two fingers, still holding on to the end with your thumb. Make about 10 to 20 wraps.
Carefully, making sure not to invert or tangle the loops you’ve made, slide them off your fingers and pinch the loop into a line, or hank, shape. Hold one end of the hank in your off-hand fingertips, with the loose end of the yarn pointing into the palm of your off hand, and start wrapping the yarn around the center of the hank. When you’ve made about 10-20 wraps again, start wrapping diagonally. Every few wraps, rotate the hank in your off-hand slightly around the axis of the central hank so that the diagonal wraps precess around the ball.
Continue wrapping diagonally, precessing around, until you run out of yarn. Before long this will cover up the starting hank, so you will need to switch your grip to the outside of the ball as you wind it. Every so often as you work, especially towards the beginning, pull an inch or so of the loose end out of the center to make sure it pulls smoothly; if it catches, you can either pull harder until you pull out a knot (but not so hard you break it), or unwind and try again. If your yarn is generating a lot of knots, try method 2 below instead.
The cardinal rule is to always keep track of your loose end and never, ever wrap over it. The final product should have a recognizable top–where the loose end comes out–and bottom, with divots pointing towards the center. When you are done, tuck the outside end of the yarn under the last couple wraps to keep it from unwinding.
2: With tools: You will need an object like a sharpy marker, USB stick, broomstick, etc. Anything that is smooth, roughly cylindrical with a 1cm-2cm diameter, and tapers or is straight to the end will do. Hold the object in your off hand and hold the end of the yarn against the object with your thumb. Wrap the yarn straight around the object (perpendicular to its long axis) for 10-20 wraps, then start wrapping diagonally as above. Slowly rotate the object with your off-hand as you wrap to make the wraps precess around the ball. Wrap until you are out of yarn, tuck the outside end in, and slide the ball gently off the object. Because of the extra space in the core established by the object, this method results in a smoother-unwinding ball that is less likely to form knots. The core object also gives you better leverage to hold onto and smoothly turn the ball in the early stages of winding.
Random note 1: Despite many advantages, center-winding yarn balls/skeins have the disadvantage that as you work, you remove the center, and the skein loses structural integrity. A matching advantage, however, is that you can re-ball your yarn while it is attached to the project, without ever unwinding the whole thing. Just start with the yarn leading to your project under your thumb.
Random note 2: If you already have a center-winding skein, either from the store or that you have made, and you want to work on two socks/gloves/whatever at once from both ends of the yarn, you can either a) draw from both the outside and inside at once, or b) re-ball as above, holding both ends together and winding both strands together, being careful to keep the tension even between the two strands. They will tend to twist, so you will need to periodically stop and untwist things. At the end of the winding, you will have a loop at roughly the midpoint of the yarn; tuck it under the other wraps for now and cut the yarn only when you have finished the project.