Friday 28 October 2011

Crossbow Test Shot

Before binding on the prod I wanted to test the bow, but first I needed to make a groove for the bolt to run in. Some crossbows have a groove, others have a small piece of horn or somesuch with a notch for bolt at the end of the 'runway' 'track' 'barrel' 'channel' (or whatever you want to call it) with the back end of the bolt being held by the trigger mechanism.
The trigger mechanism I'm using doesn't actually hold the bolt, so I need a shallow groove, the advantage of a groove is that it lowers the bolt slightly so the string is then pushing the bolt on it's centre-line rather than it's bottom edge, which can cause the string to go under the back of the bolt or the bolt to bounce upwards.
I made a shallow square groove using a plough plane which has a very narrow blade. My Brother gave me the plane for my Birthday many many years ago specifically for that purpose. I rounded the groove using an arrow shaft with fine sandpaper wrapped around it. This wasn't working particularly well so I took a 7.5mm drill and ground the butt end of it at a slight angle on my small grinding wheel, this made an excellent scraper/chisel for working along the groove.
The prod was temporarily bound on with some rubber strip (cut from EPDM roofing sheet, but old inner tube is much the same) I cocked it and put the bolt on, making sure the back of it was just in front of the string, so that the string didn't pop up and knock the bolt off the runway.
THWACK... it smacked into the target at very close range, the trigger pull was smooth and easy, there was no real kick and the bolt was buried up to the flights in the target. Excellent!
I'm now working on the detail. I'm adding a sliver of Ivory (from an old piano key blank) at the front face of the trigger slot which retains the string when the bow is cocked. This will effectively block off the groove in which the bolt rests, stopping it from being pushed back too far. A clip of Ash will also reach over the top of the trigger slot and press lightly on the bolt to stop it falling off or bouncing about, I may incorporate a back sight into the retaining clip. The clip also stops the trigger peg coming out the top of the stock. I shall probably just glue it in place with hide glue. One advantage of hide glue is that it can be undone with heat and humidity, whereas epoxy is rather permanent.
Once I've done these few bits I can bind the prod in place and really test it.
Pics tomorrow.

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