The patent office fire of 1836 wasn't a complete loss. In the years following the disaster many patents were recovered in some form or another. The lock patents specifically had only a handful of documents recovered, but those partial records are giving this project a great head start.
The Cambells of Charlsetown, MA were lucky enough to have both a drawing and a description of their lock preserved and even digitized. As best I can tell, however, no transcription of the letters patent existed before now. In the public Zotero library, you can now read the (almost) complete letters patent for this lock. And, with a drawing and description, we can actually understand how the lock was meant to function.
The Cambells' lock requires both a key and combination. The key in this case is a fairly dumb implement, just designed to apply force to the bolt to pull it into the body of the lock. This was made impossible by the blocking bar that holds the bolt assembly in place, and sits behind two combination wheels. The two combination wheels have eight possible positions each, with 7 false gates and one true gate. The false gates aren't deep enough for the blocking bar to drop into place, so, if you don't have the right combination, you won't be able to pull the bar flush to the face of the lock. With the right combination, the blocking bar can be pulled into the true gates of the combination wheels and the bolt assembly can slide over the blocking bar to fully retract.
Another important feature was the ability for the user to change the combination themselves. It's clever! For its time it was damn clever. It's also readily beatable, but it can also be improved on. In my patent diving I have seen much more difficult to manufacture, sillier, and less useful, contraptions than the Cambells'.
Now that I have a good drawing and a clear description of how this lock worked, I think the next logical step is to build one!
This is one of the things I find most exciting about the X-Lock project. Not only do we have the chance to restore missing parts of the patent record, but we have the chance to hold in our hands the labors of long forgotten inventors.
This post is part of my ongoing research into the security patents lost in the Patent Office Fire of 1836. You can find more information at X-Locks