Using medieval bow making technology to improve performance on the springpole lathe
When I built my springpole lathe I decided to make it larger and heavier than Underhill’s model. The capacity increase has really paid off as I can turn up to fifty-five inches between centers and and swing twenty. However, there was one thing that I overlooked. I never gave a thought to the diameter of the springpoles. With the added weight of the crossarm, treadle and larger workpieces the one inch diameter is a bit on the “skinny” side, especially as the original main spring was made from yellow pine.
The yellow pine is more than adequate in the area of stiffness. But after about a month, embrittlement set in and, SNAP went the original mainspring pole. The I tried white oak. It had plenty of flexibility. Too much in fact. So, ultimately I used some bowmaking techniques to improve the performance of the mainspring while staying within the 1″ diameter. I’ve used both ash and hickory. I’ve split them in two, then glued them back together. The increase in stiffness is remarkable. I’ve joined three pieces to form a sandwich of hickory and ash. The result was a strong, durable main and secondary spring that has performed extraordinarily well for more than a year.
Rounding an eight foot long 1″ square block is best accomplished with a stale engine. Most people don’t have stale engines or rounders, so they opt for the next best thing, the drawknife. Well anyone whose attempted to shave an eight foot workpiece on a conventional shavehorse, knows that it can be quite a challenge. So, I remembered a video I had seen on YouTube of French Medievalist Longbow maker Denis Mairine using a shave horse that allowed him to work in a standing position on overly long, thin workpieces. It is simply a ramped bed, legs that support the ramp and allow for some height adjustment, a lever board and some rope. In fact it would probably be best described as a rope vise that has been specifically designed to hold this particular type of work.
Note that the drawknife position is just about ergonomically perfect. That said, it does get a little bit tricky standing on one and a half feet. But hey, this certainly is no problem for a springpole turner.