If there is one advantage to plying from a center pull ball it is that there will be no left over bits of singles yarn sitting on one of the bobbins. The technique is best for smaller balls of yarn simply because it's hard to hold a large ball while controlling the way the yarn feeds off the ball and the tension of the yarn while the plying twist is being inserted.

There is only one piece of equipment needed for making a center pull ball and that is a ball winder or a nostepinde. A hand cranked ball winder has the advantage of being faster for most of us. To wind a ball for plying, release the tension on your bobbin, thread the yarn to the ball winder and crank it. Be careful not to lose the inner end of the yarn down inside the ball. Ball winders have a slit to hold the yarn but sometimes this fails and the end is missing. I like to put a little piece of tape over the inner end of the yarn to make sure it stays in place. If it does go missing, rewinding the ball will reveal it.

You may wind the yarn off the bobbin either from the side of the wheel or through the orifice. Either way, you may have to tie your flier down to prevent it from turning and fouling the yarn. Winding off from the side is preferable as it eliminates having to stop and change hooks. Winding off through the orifice will not change the twist of the yarn as long as the flier is not rotating.

To take the yarn off of the ball winder, locate the inner end which will be at the top of the ball when the ball is on the winder. Wrap the inner end securely around the thumb of the hand that will be holding your fiber supply for plying and push the inner end through to the bottom of the ball while sliding the ball onto your thumb. Pushing the inner end through to the bottom of the ball allows the yarn to feed from the inside of the ball easily. Tie the inner end of the yarn to the outer end.

If you plan to set the ball of yarn aside to ply later, slide it off of your thumb and onto a core such as an empty bathroom tissue roll or a rolled up piece of paper. When you are ready to ply, slide the ball off of the core so that the inner end of the yarn is at the tip of your thumb – this is the same way the ball was on your thumb when the ball was taken off of the ball winder.

When you ply, one end of the yarn will feed from the middle of the ball and will be tensioned by friction from your thumb. The yarn feeding from the outside of the ball must be tensioned by the other fingers of the hand holding the ball. Use your index and middle fingers as brakes to stop the outer strand of yarn from winding off too rapidly, to hold the ball on your finger (the forward pull of spinning tends to pull it off the thumb as inner tension decreases), and to tension the yarns just prior to inserting plying twist.

Note that the outer strand of yarn must feed off at a rate equal to the circumference of the ball. So if your ball has a circumference of 6 inches (15cm), then that is the length of the yarn that will feed off between opportunities for your fingers to brake the yarn. Meantime, the inner strand is feeding off in much shorter lengths so drafting back is necessary for tensioning the yarn prior to plying. The length of this drafting motion needs to be shortened up as the yarn is plied and the circumference of the ball decreases.