To avoid over-twisting, should I tighten the drive band to slow down the flyer then tighten the scotch tension to avoid over twisting?
A: If you feel that the yarn is over spun, or too hard, check first to see if plying it will soften the yarn sufficiently. Plying removes between a third and half of the original twist. As you are spinning a single, stop and pull out of the orifice about 12 inches and fold it from the middle and allow it to ply back on itself.
This will show you what a plied yarn would look like from this particular single. It is prudent to knot it and remove this little plied piece to keep for reference when plying - IF you are happy with the results.
If it is still too tightly spun for your purposes then you have some choices, that pertain to the three factors of twist - see answer one. a) Move the drive band to a slower drive whorl (a larger one) if it is available. This changes the first factor b) Treadle slower c) Draft faster and feed the yarn toward the orifice faster d) Prepare your fibers better, These b,c,& d all change the second factor e) Use a faster wind on method ie-the long draw, This changes the third factor of twist.
Sometimes it takes a combination of actions to get the correct amount of twist.