"Projects" at georgesbasement.com

2. Haeberle & Schmidt Corner Brace
Starting point - incomplete corner brace
U.S. Patent No. 859,059: Haeberle & Schmidt corner brace
Missing removable piece of Haeberle & Schmidt brace
Final result
Basically what I started with (not the actual eBay image).
US Pat No. 859,059 - all together.
Here's what I was missing.
The final result.

Dimensions of missing thumb nut
Plug gauge
Thumb nuts - compare knurling The first step was to reproduce the thumb nut that holds the removable piece down by the chuck.  This wasn't easy, because I did not want to remove the existing thumb nut from its place.  I had to guess at some of the dimensions, such as the pitch of the threads and the best "tap drill" diameter.  Then, that's a blind tapped hole in the thumb nut.  At least, the threads are right-handed.  You will note that I had to modify my estimates as I went along ... and make a plug gauge to check the progress of my threading.
I do not have any means of knurling, so I used the lathe as a shaper and chased the grooves one at a time, using the lathe's bull gear as a divider.
End dimensions of removable piece
Thumb nut & end piece in place
My "new" removable piece was donated by an old, decrepit Stanley Rule & Level corner brace, where the end was smaller than it should be, and threaded 7/16-22 to boot.  Therefore, I had to make an adapter to fit the smooth interior of the socket into which the removable piece had to fit, and it had to have a key to prevent rotation of the universal-joint housing.  The adapter's internal thread is almost as large as its external diameter, and it had to be a tight fit on the end of the removable piece.

Design of original head & latch
Connection - open
Connection - latch closed
Head closed & latched
The original patent's latch was flimsy ...
I had to design my own arrangement.
Here the latch is in the locked position.
There's a spring & ball to hold the latch.
There are several sleeves and packing pieces to take up the slack in the very sloppy fits of the original brace's various pieces. They're bronze, salvaged from old tensile specimens.
The brace all together
Patent date
US Patent 859,059, July 20, 1906
The pieces go togther now quite nicely, and the brace is fully operational in either configuration - as a straight brace or as a corner brace.  If there's one nagging flaw, it's that the split screw over which one or the other of the two thumb nuts fits is insecurely attached to the universal joint housing and falls off relentlessly during any changeover.  The patinas of the two portions match pretty well, except for the freshly made pieces, of course, and the wood handles are good matches for each other.  Maybe the original removable piece was also made by Stanley ...