Made pretty good progress with the tiller this afternoon, but what I really want to get to is the lock mechanism. One came fully assembled and the other in pieces, so first thing I put that one together, starting with the claw assembly. There are four parts, the two aluminum plates, a steel tube spacer, and a screw. I used the 5/16" axle pin to align the parts and tighten up the screw snug, but not so snug I'd risk stripping the threaded aluminum.
There were no actual mounting bolts or pins provided, only pins that are just the width of the box, 1.25". That is not a problem, as deciding whether to use bolts or pins and how long they need to be is pretty dependent on how the tiller is built, and bolts are cheap. As currently designed, the front axle for the toggle is 1/4" diameter, and the rear axle for the trigger and claw is 5"16". In the photo above a 5/16" stainless steel tube is inserted, more on that later.
On to the trigger and compression spring:
The box looks to be milled from square aluminum tubing with 1/8" walls, with a lighter weight back plate pinned on. The sole function of the back plate is to secure the spring. Of course the ancients didn't need no stinkin' spring and let gravity do it's thing, but I sure like the lightened trigger and the solid click of the lock engaging. Putting the spring on the screw was a bit of a challenge, eventually I figured out to use the trigger as a lever to force the spring down over the screw. The front of the spring fits into a cavity on the trigger, I don't think it's going anywhere.
I planned to install the unit completely stock for the purposes of testing, but I found myself making one alteration right away. The screw provided to secure the spring sits very proud of the back plate.
I'd cut my cavity for the lock mechanism to fairly tight tolerance, and I did not want to carve a channel to clear the head of the rounded screw. So I filed the screw head as flat as I could, cut a slot for a screwdriver with a thin cut-off wheel in my Dremel, filed a bit of a recess around the screw hole in the back plate, and lovingly suggested the final position with a couple of taps from a ball peen hammer:
Above you can see the provided place-holder axle pins in place, the 5/16" pin is steel and the 1/4" pin is brass. I know that through the development of this design John was concerned with clearance of the cock-feather of commercial three fletched bolts, which is why he went with a smaller axle hole for the toggle in front, just for that sliver of extra tolerance. Keep in mind I haven't locked or fired this design yet, but my initial observation is that it is quite robust, and in fact the cock feather clearance may not even be much of an issue. The front of the toggle is one inch in front of the teeth, and I don't have any commercial bolts with fletches closer than 1.25" to the butt of the bolt. The 16.5" aluminum shafts I most often use have the fletches over 1.5" from the end.
So that brings me to my only other complaint regarding this otherwise totally sexy lock mechanism: it isn't a drop-in solution. Sure you can assemble it outside the stock and play with the action, and with the short pins provided you can drop the whole unit in to test fit in the cavity in the stock, but since the axles are also needed to secure the whole assembly into the tiller, you still have the fiddly task of lining up the components inside the tiller to get the axles through. This is actually more of a challenge inside an aluminum box inside the tiller than what I'm used to, and there are three parts to line up, fighting a pretty stiff compression spring. This is a bit of a pain in the shop, doing it in the field, for whatever reason, would be a real challenge.
So, remember that 5/16" stainless steel tube I was talking about earlier?
The inner diameter of the tube is just over 1/4". So, without further modification to the mechanism, I now can have both axles the same diameter, and at least the most troublesome bits, the trigger and claw assembly that share the rear axle, can be secured outside the tiller and I just have to mess with lining up the toggle. This is how I will install it for testing, to keep it as stock as possible, but In tandem I'll be developing a full drop-in unit, with toggle and front axle drilled out to 5/16" to accept the same tubing. I think there will still be plenty of steel around that part for a margin of safety.