mini-crossbow part 1 – the prod/bow/limb

Funny how things won’t let go sometimes.  The story starts, ‘ Many year ago, when I were a lad……’ of ten or eleven, I decided to build a crossbow but mum found the twigs I managed to snap off the privet hedge sticking out from beneath my bed, and that was that.  Then, when I was in my teens, I found a book of wood-work projects in the library and there was a how to make a cross-bow project!  ‘Sorry’, said the librarian, ‘you’re too young to take a book out of the grown-ups section in the library’.

Oh well, time passes but I have finally, after many years, gotten around to building a child-sized cross-bow.  To make things a little more demanding I decided to make the crossbow with a yew bow (called ‘prod’).  In the end, I made the whole thing, stock and prod, from the same piece of yew.

At the outset, I want to say a grateful thanks for all the advice and encouragement recieved from the craftsmen and women of the Arbalist Guild forum.

I have carved yew many times and it is a beautiful wood to look at but is very hard and particularly prone to cleaving, which can be used to advantage when roughing things out as you can split huge chunks of waste away very easily – most of the carving for this project was done with a hatchet. I have never needed to bend yew before and it is really strong and really stiff.  In the end the prod was cut to 15mm in the centre and tailed down to 5 mm at the ends and still needed two hands to flex it across my knee  but to string it needed a jig and pulleys – a 10mm thick (average) stick needing a pulley to bend it!!!!!. Oh, it is also very toxic – leaves, berries, sap, wood, bark and root, all very poisonous (sawdust too). I digress.

The important part of a yew bow is the sapwood – it absorbs the bending forces of the spring.  The surface of the sapwood must be all of the same growth-ring  (layer) of the wood and must be undamaged. It forms the part of the bow that faces away from the archer/shooter. Any break in the sap-wood will allow a seperation between the layers and lead to catestrophic failure.

As this project was for a mini-bow, the sapwood was too thick and was reduced in thickness to about 3mm (1/4 “); this was the longest part of the project as the surface of the sapwood then needed to be finessed so that it was all from the same gowth ring and was undamaged.  The shape looked like a ‘dogs hind-leg,’ as it followed the contours of the timber, up and down, all over the place, but the on first prod I made, the top surface was carved nice and smooth and it snapped as soon as I bent it hard. Funny though, when the second prod was strung, the tension resolved the shape into a lovely smooth cuve.

Now the other important bit.  On such a short prod (17 inches, or 42cm), the prod needs to be pre-formed into a curve as it can’t bend enough to work as a bow.  There are three ways to do this, all use the application of heat – hot air gun, steaming, or boiling. The prod needs to be heated enough to soften the lignin in the cell walls, the wood can then be bent into a new shape and left to set. Both hot air and steam dry out the timber so I opted for wrapping the yew in towels and pouring boiling water over it for a while – I kept it hot for about 15 minutes, and then very quickly (speed is ESSENTIAL – more than 30 seconds was too long, don’t ask me how I know….)  bent it into a form made of an ash batten attached to a few nails in a baseboard.  The batten was initially sprung to a 3″ deep curve  on a base-board; this curve was then marked out and the nails driven in so they stood 2″ proud of the board (note, I needed a 2” deep curve but bent extra in to allow for spring-back). The batten was clamped to the nails,  the hot prod was clamped to the batten; this way the prod took the curve of the batten and the batten took any nail-marks – it sounds too simple to work but it was very effective, however the prod sprung-back to a very shallow 1.5 inch curve after cooling for a few days – needed more heat to cure in a deeper curve, probably.  Interestingly the prod seems to be much more flexible now and can flex to a full draw of 5 inches but would only bend half this before boiling.

Once strung with a temporary string, the prod was put to one side in order to make the stock.  Who am I kidding, I couldn’t wait to test it and spent much time firing pencils off a piece of 2×1 that I lashed the prod to. Once I got that out of my system I measured the normal draw on the prod at 4.75 inches and set to work making a medieval-style of stock, but that, together with some pictures is part two of this post. In the meantime, why not spend some time perusing some beautiful medieval crossbows in my pinterest clipboard on decorative weapons at  http://www.pinterest.com/avenuew/decorative-weapons/

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