Thursday, 20 October 2011

Crossbow Prod

The prod is still pretty stiff so I checked the thickness and took it down some more, going 1.5mm thinner for each 3" along the bow from the centre.
It still seemed rather stiff, expecially in the centre so I took another 3/16" off the lower edge. I then adjusted the thickness taper from the tips which seemed about right increasing thickness by just 1mm for every 3" this time.
The pics show it on the tiller, but bear in mind it's not braced, the string is just slipped on and the bit of curve is natural deflex. It certainly is bending near the middle now and I'll probably work the tips and mid limb a bit more next.
It's going to have to bend a fair bit more yet, so I've glued some rawhide on the back using hide glue, as in this previous post. http://bowyersdiary.blogspot.com/2010/04/glueing-up-ashcherry-bow.html

The rawhide is a huge bone shaped dog chew from a pet shop soaked in warm water to unknot it. It's pretty slippy stuff to handle and gluing it on and binding it with string until it sets is a messy job. The glue gels quickly and it feels like it's not going to stick, but a waft with a hot air gun when it's finished helps to re-liquify the glue. You can see from the chalk marks on the wall that it is bending about as much as my other bows, so I'm not sure it can take much more.

The last pic shows how the upward curve of the bow moves the string line so that it won't press down too hard on the stock and waste power. The down side of this is that the bow tries to twist on the tiller.
It also shows some of the dark streaks on the belly of the prod, these are shallow cracks which hopefully won't be too much of a problem as they are longitudinal. There was also a knot which I filled with sawdust/epoxy mix.
I believe the stock of a medieval crossbow was called the tiller, being long and straight, maybe it was reminiscent of a boats tiller, and maybe then got applied to a tiller stick used for pulling back the string of a long bow when checking the curve of the limbs.

1 comment:

  1. I started to make my first crossbow and it look so good.
    Medieval Crossbow

    ReplyDelete