As promised, a photo of the finished prod. In this image you can see it lashed onto the finished stock. The small Ash plate at the front is a yoke that protects the prod from being damaged by the lashings – remember it needs the pale sapwood to be undamaged to prevent it failing. Note too that the centre of the prod is thickened into a ‘handle’ like on a long-bow, I have since found out that this is incorrect.
To keep things as simple as possible I opted for a trigger mechanism known as a pin-lock. This is super simple. The bow-string sits in a curved groove cut ACROSS the stock; there is a hole drilled below the groove with a dowel in it. The dowel is the pin, and the bottom of the pin rests on the trigger. The trigger pushes the dowel (pin) up and the dowel pushes the string out of the string-groove.
The sketch shows a section through the stock (cross-hatched) that, I hope, explains things a little clearer. The biggest isue is that the pin keeps falling out of the hole if the bow is turned upside-down – fortunately the bolt-keeper (the long triangular spring that holds the quarrel/arrow/bolt on top of the stock – see second photo) also keeps the pin from falling out.
To keep the trigger effort low the trigger is installed at a shallow angle but the angle shown is really too shallow and the trigger pressure needed to release the string is tiny.
Photo 2 – the whole thing, note the bolt-keeper on top of the stock, it holds the quarrel onto the bow when the bow is tipped up, or down, when aiming – this is important as the string is tucked into the string-groove and the quarrel cannot rest against it. The two studs (one each side of the ‘keeper) lift the string up to the centre of the bolt and prevent a miss-fire as the string cannot pass under the bolt – it does pass below the bolt without these studs because I did not cut a bolt groove. The style of crossbow I copied uses a flat plate for the bolt to rest on but ‘normal’ bows just cut a groove along the stock for the bolt to drop into.
When I fit a proper string I will remove the studs as crossbow strings are chunky and do not need lifting up to strike the bolt in the way this thin, temporary, string does.
Photo 3 – side view showing trigger, bolt-keeper and pivot-pin (just visible as a darker circle on the curve of the fore-grip. The deep triangular notch that the trigger is coming out of is cut because the trigger runs in a channel wide enough for it to pivot up and down in. There are three ways to cut this channel – split the stock in half and hollow it out – crossbows are frequently laminated so that approach is not as uncommon as you might think; drill all the way through from the top diagonally and fit a covering plate; or do what I did and blind- drill diagonally ‘up’. This last approach requires a notch for the drill to work from and at a later date I will cover this over with a plate of contrasting timber.
The prod itself sits snugly in an open ended socket cut about 5 degrees from vertical – the prod is just tipped a little bit forward so that the string gently rubs the top surface of the stock. This is greatly helped by stringing it so that the string runs off the top edge of the prod and loops under it – called a side-nock. This also has the advantage of cutting only one notch from each end of the prod – a diagonal notch (as deep as the string is thick) on the under-side of the prod.