On 11/3/2013 12:09 PM, rkg wrote:
Is this well-known to those who well know it? What do the tennis-ball manufacturers do? R.
There is a very revealing video on YouTube called "How Tennis Balls are made" (http://www.youtube.com/watch?v=yuZI9zgY4wM) that shows the processes inside a Wilson factory. The cutting and application of the two pieces of the felt cover are shown from 1:29 to 1:50. Here is a transcript of the narration: The felt cover of a tennis ball is made of two dumbbell-shaped pieces of material. These pass through a glue bath and will shortly be applied to the rubber ball. Covering is either done by hand or by machine. Hand covering is more accurate, and this can be seen by the very consistent width in the glue line that runs around the ball. Despite saying "dumbbell-shaped" the pieces shown in the video (especially clear around 1:42) seem to be convex; the boundary looks like two semicircles joined by straight lines. Perhaps this varies among manufacturers; the Penn balls I have at hand seem to be formed from nonconvex pieces. In fact, a brief perusal of images of Wilson tennis balls suggests that they make balls with varied curves. After watching this, I'd guess that the shapes are the result of refinements made in practice without any formal mathematics intervening. -- Fred W. Helenius fredh@ix.netcom.com