China, for all its inventiveness in some ways, was ultra conservative in others (still is for that matter). That Han crossbow lock was still seeing service 1200 years later (!!) during the Ming Dynasty (1368-1644 AD). "If it ain't broke, don't fix it." as they say! The design is simple and efficient what more can one ask?.
I'm going to beta test John's lock in a Ming Dynasty crossbow replica featuring a six-leaf loose laminate prod made from bamboo laths:
Stephen Selby's commentary on the pages is just enough to tease a crossbow builder!
I've had some other folks at the Asian Traditional Archery Network translating some of the text of the illustrated encyclopedia sections which describe the design, construction and use of that military crossbow. The article gives detailed Chinese measurements which are also being converted into metric and English measurements. Many thanks to Peter Dekker and Justin Ma for their translation skills in this endeavor.
With some of the measurements in hand, I used a drawing program to scale up the illustration of the tiller (from the second page) to "full size", and printed it out. The sketch is at best a 'cartoon', but does give the basic profile shape of the tiller, subject to some changes to make it actually functional
I also found (after much searching) appropriate bamboo slats that didn't cost an arm and a leg, and a second arm and leg for shipping! I got three 6 ft x 1-3/4" x 1/4" slats for $10, and another $10 for shipping!!! They're coming from an outfit in Orlando, John!
The prod shown in the encyclopedia is six laminations: 30”, 29.5”, 28.5”, 22.5”, 17” & 12” There is no detailed measurement of the thickness of the laminations, but ones I'm getting will give me a nominal "Stack Height" of 1.5”. What the draw weight will end up is anyone's guess. The power stroke from the back of the prod to the latch is 9.25". We're looking for a brace height number. Six hundred years ago, this style of crossbow was described as "waist-braced" and there are illustrations on how to use a rope around one's waist, and one's feet, to bend the prod with a bastard string while an assistant slips on the operating string.
Now to go find some appropriate "plankage" for the tiller. Basically I need a 2x6 about 30" long. Maple? Mahogany? Oak? Should I use a single 2x6 plank or glue up two 1x6s? Single plank is historically correct, so I'll probably go that route.