Regarding whorl-hole taper: In ancient times, whorls were typically attached to their shafts by "friction-fitting" alone, and without adhesives. Since spindle shafts are typically tapered, at least at one end or both, the whorls often had tapered holes to help increase the friction surface between the whorls and the shafts. This is generally indicated in whorls by a larger central hole opening on one side of the whorl or the other. With whorls that are flat on one side and convex on the other, the larger opening is typically on the flatter side - the flat side of the whorl usually faces the center of the shaft when mounted on a shaft.
Where it exists, (not all whorls have it) central-hole taper can be determined by two methods:
Method a) By direct measurement of the hole entrances into the whorl - usually indicating one hole entrance slightly larger (greater diameter) than the other. This can be measured with inside callipers - however the differences can be quite slight. Direct measurements of this sort can then lead to the calculation of a hole-taper angle.
Method b) By gently inserting a tapered stick (1/2" or 5/8" dowel shaped like a pencil point) into the hole to see just how far the stick penetrates the whorl hole. This penetration depth can be marked on the stick with a pencil line. The tapered stick can then be placed into the other end of the whorl hole to indicate the penetration (either greater or less than the previous mark). Where there is a difference in the depth of penetration there is usually some hole taper. Not as precise as direct measurement but useful non-the-less - especially where the margins of the whole entrances are rounded or irregular.
Regarding whorl balance: To function with good stability in rotation, whorls need to have an even distribution of their weight around their central hole or perforation - good weight concentricity. A whorl can "appear" to have it's hole off centre but the whorl may still have good/even weight distribution around it's central hole. This is particularly true of whorls made from old broken pot shards that have been re-worked into disks for whorls.
Method a) One way to get an indication of a whorl's weight concentricity is to mount the whorl on a shaft and test-spin the completed spindle. If the spindle wobbles significantly then the whorl is probably not well balanced - (the weight of the whorl is not evenly distributed around the shaft hole). If the spindle rotates through most speeds without significant wobble then the whorl is probably well balanced.
Method b) A second way to determine a whorl's balance is to place a piece of fine wire (a piece of stripped copper house wire 6"" long and 1/16" or less in diameter) on a flat surface and try to balance the whorl on the wire. If the whorl has a flat side then lay the flat side of the whorl on top of this wire. Usually the whorl will topple to one side or the other of the wire and come to rest on the table - this is ok. Just roll the wire under your finger until the whorl topples to the other side of the wire. When this occurs do not disturb, but look through the hole to see if the wire crosses the central hole approximately at it's center.
Now, do the same again, but with the whorl rotated 90 degrees. This tests the other direction across the whorl for weight distribution. Here again, if the wire can be seen crossing the hole at about it's center, then the whorl weight is relatively well distributed in this direction also.
Basically, the further down the shaft a given whorl is placed, the more stable the resultant rotation. If you want to be "rigorous" with your spin-testing for whorl balance, then mount your whorl closer to the top of the shaft - e.g., within 1.5-2.0" of the yarn-anchor area.
Many thanks to Tom Forrester for this information!
