Sunday, April 08, 2012

Understand the Spindle! Part III

The next set of questions has to do with how the spindle is spun-up, and how much energy is in the "flick".

There are several "finger flick" motions that can be used to spin up a spindle.  These can give a spindle with a 2 inch whorl some 400 rpm.  That means they can give a spindle with a 1 inch whorl as much as 3,000 rpm depending on how the flick is delivered.  However, a smaller whorl diameter is likely to have a smaller diameter blade (the chopstick like stick in a spindle system).  A smaller diameter blade has a smaller circumfrance, which must rotate more times during the flick, so that a smaller diameter blade can produce much higher spindle speeds.  On the other hand, large whorls will need larger blade diameters to provide the torque to get  larger whorl rotating.  Thus, if you want to spin fine yarns fast, smaller whorls allow smaller diameter blades, which allow spinning the spindle faster during the flick.

In short, it is a system, and by changing the diameter of the whorl and the blade, we can make spinning one kind of yarn easier (and spinning another kind of yarn more difficult.)

The amount of energy that can be delievered to the spindle in one flick is limited.  As the weight of the copp grows, that weight and the weight of the spindle must be both be spun up.  Since some of the energy goes into accelerating the copp, there is less energy to accelerate the spindle.   Thus, as the size of the copp grows the spindle speed is reduced.  This effect can be reduced by using a removalbe  whorl.  Then the whorl is removed when the copp reaches a critical size and spinning continues using the copp as the "whorl".  This allow faster spinning and bigger copps to be built.

The total weight of the system is limited by the tensile strength of the yarn being spun. Fine, soft yarns can not suport as heavy a spindle system as a hard spun cord.  Wool cannot support as heavy a spindle system as linen, cotton, or hemp, and so forth.

On the other hand, spinning hard spun cords require heaver spindles and whorls with longer lever arms to insert twist into yarns with more spin rigidity.Thicker yarns require heavier spindles to hold the fibers in alignment as twist is inserted. (Even with woolen yarns, some parts of some fibers have to be held in alignment so that they can be wrapped around each othe to generate the friction to hold the yarn together.)

Thus, we can design or select a spindle to facilitate the kind of spinning that we want to do.

For strong/ heavy cords/heavy plying : A heavy spindle with a large diameter whorl such as a Navajo or dare I say it?  (I dare!) the old Ashford spindles.

For singles for 2-ply worsted yarn:  This is where the common modern designs excel with ~3" whorls and total spindle running weights ~2 oz.  Cupped or weghted whorl rims allow slow, carefull drafting for spinning very pretty yarns.

Lace singles (6,000 - 12,000 ypp) :  Here modern spindle designs get schizophrenic, with light weight but long lever arms.  I like a removeable whorl bead (sometimes a metal nut) with a total spindle weight near 0.7 oz. Whorl diameter varies from 0.5 to 1" depending on the desired yarn texture. As the copp grows, I take the whorl off and allow the copp to act as the whorl, so that the final weight of blade and copp of 560 yards is only a few grams heavier than the original blade and whorl weight.

Fine Singles (grist greater than 12,000 ypp): Supported spindles (Russian & Tahkli ) work very well, but drop spindles can be much faster.  The trick is to use thin blades and small whorl beads.  In particular, top spindles spun up with thigh rolls can allow rapid production of fine singles.


Kathe Lewis said...

Hi Aaron,
I don't quite understand what you mean by "lever arm" in the paragraph on lace spinning, would you care to explain, please?
Kathe, DK

Aaron said...

Leverarm is how far the mass is from the center of rotation. If the mass is close to the center of rotation, then the mass has only a small amount of leverage, and for a given momentum, the result is limited torque to insert twist If the mass is rotating far from the center of rotation, then the mass is acting through a long lever arm and has plenty of torque to insert twist even if the yarn is quite "rigid".

If there were real easy, you would not need a nerd like me to bring it up. Rotational dynamics are difficult.