TPI and Wheel Ratios

Most spinning wheels have more than one whorl on the flyer. This allows you to spin at different twists per inch more easily. This is similar to the various reed sizes that are available to handweavers, allowing them better control of the sett of their cloth.

I am spinning this semi-worsted yarn on my old Lendrum spinning wheel. The whorl size that I'm using spins at a ratio of 8:1. This means that every time the big wheel makes one revolution, the smaller whorl goes around 8 times.

In order to spin at 8 twists per inch (TPI), every time I treadle, the larger wheel goes around once. With the worsted spinning method that I am using, I advance my right hand down 1 inch. This allows the wheel to put 8 twists into that 1 inch of yarn. By maintaining an even treadling, and moving my hand at a consistent rate of 1 inch, the finished yarn will be spun at 8 TPI.

You can check this at any time, by stopping the wheel. Draw a bit of yarn out of the bobbin and let it spin back onto itself. Count the number of twists in the yarn. It should be at 8 TPI.

If I wish to spin at a lower TPI,
e.g. 4 TPI
then I can advance my hand down at a faster rate.
Sliding my hand down 2 inches for each treadle, will produce a yarn of 4 TPI.

You could conceivably spin just about any twist or thickness of yarn using only 1 whorl size, but it is easier to select the whorl ratio that is closest to your desired yarn. If you wish to spin a high twist yarn of 18 TPI, then choosing a high ratio whorl would make your spinning much more effortless.