A while back, I thought about spindles. I went around and played with a bunch of them. I went into the shop and made a few. My conclusion was that they were toys. I concluded that modern spindle designs were not really tools for serious worsted thread production.
I was missing two technologies that are essential to the system. One is the distaff. The other is a removable whorl. We find whorls made of fired clay, metal and stone around the world, and we tend to assume that that entire spindle was lost, all at once, and then the wooden shaft rotted away, leaving the whorl for us to find.
However, looking at accounts of spinners in the Highlands, they put a whorl on the spindle, start spinning, and as the copp builds, they take the whorl off, put it in their pocket, and let the copp act as the whorl. This allows them to produce longer continuous threads. This is a tool for serious worsted thread production.
And, it is easy to lose a whorl out of their pocket.
I have come up with a spindle design that I like much better than any other that I have tried.
I start with a spindle shaft about 12 inches long. It has a spiral groove for the thread (because hooks catch on everything and a half-hitch causes the thread to lose 40% of the thread's tensile strength. If you design the spindle assuming the use of a half-hitch, then you reduce the length of the thread that can be spun on that spindle by 40%.) The groove is made with a small knife and a rasp.
I go to the hardware store and I buy 2 threaded nuts, one big, and one small. I thin the spindle down, leaving a bulge at the bottom. The bulge is large enough that the threads of the large nut will catch on it and tapered enough that I can thread the small nut on it. Threaded nuts for bolts are very cheap. You can afford to buy a few in the event that your "spindle whorl" falls out of your pocket.
I "screw" the large nut on the bottom of the spindle and start spinning.
The metal nuts have enough weight to spin well. Their concentrated weight means that the spindle tends to spin fast - much faster than with modern disk-whorl designs. So fast, that you can not draft fast enough to keep up with it -- unless you are spinning fairly fine and have a distaff to help you draft faster. This is not a spindle for beginners.
Here (http://www.youtube.com/watch?v=Mp78jcvJizA) and here (http://www.youtube.com/watch?v=i4lzA_aBHCI), even after their copp has grown, the fixed whorl tends to slow the RPM of the spindle, limiting how fast they can spin, and the weight of the whorl limits how fine and long a thread they can spin. However, it is not hard to find pictures of Peruvian spinners using removable whorls and distaves. See for example http://users.stlcc.edu/mfuller/SpindleWhorls.html
ETA: Last night, Will Taylor told me that many South American spinners use machine nuts as spindle whorl weights.
ETA: The idea