Wednesday, 20 December 2017

Prototype Trigger Mechanism

I've got the prototype trigger mechanism almost finished.
It's basically the standard 2 part mechanism, a rotating nut and a trigger. The juxtaposition of the two parts is such that the trigger protrudes horizontally from the back. The entire mechanism will slide back along the stock of the shooting machine between two rails. As it draws back to the desired draw length, the trigger will lift on a sloping peg inserted into the stock giving an automatic loose.

Alternatively the mechanism can be clamped in a fixed position, the string drawn onto it and the the trigger manually lifted to loose.
The nut and trigger are made of plywood and will only probably be only strong enough for light bows. Of course plywood is no good for the working parts so these have been faced with bits of hacksaw blade epoxied into place.

I've made the fingers of the nut approximate to an archer's fingers, and being wood, I can easilly shape them as needed. The final version will have aluminium fingers and a steel centre section and trigger.

The sheet steel sides of the mechanism are held apart by two aluminium spacers with 3mm steel rivets going through the whole assembly.
The sketch shows the approximate layout and illustrates the easiest way to get a smooth trigger action. If you draw lines from the release point where trigger and nut meet back to the centre of the two pivots (red) and arrange these lines to meet at 90 degrees this gives a line of force directly back into the pivot rather than a force which try and make the trigger either slip or jam. The trigger will pull without forcing the nut to rotate back against the pull of the string. So you just sketch roughly where you want the two pivots and then get a set square or the corner of a sheet of paper and move it around to find the required position for the sear to give the magic 90 degree angle (or do it by eye). You don't need this 90 degree angle, it's just an easy way to get it right.

Hopefully I'll get the rails built soon and try it out, mind I have mince pies and sausage rolls to make too!
Soon be time for my round up of the year, but it would be nice to get this done before then. Hoping for some Hazel harvesting over the holiday too, good excuse to get out of the house and have a pint with some chums.


  1. Hey Derek. Happy Christmas to you and yours. Did you know your reaction tick boxes don't seem to be working? well....not for me any way! All the best Paul and Cilla (Devon)

  2. Hi, Happy Christmas to you and yours too.
    Yeah, those reaction boxes seem to come and go randomly, sometimes they show the numbers, sometimes not... dunno why.

  3. Just tested it by going "incognito" so it didn't recognise it as me. I ticked interesting and it showed up.
    Then I went out of "incognito mode" and looked at it, it hadn't recorded... but then clicked on the refresh button and it showed "1" on the interesting count.
    Dunno what that proves, maybe it needs refresh clicking to update the counts?