The case starts from a rough 60mm diameter billet.
I first face off the billet.
This is done so that we achieve a flat surface, and then when the piece is turned around, we are sure that the other face will be parallele to this one.
I drill a center hole in order to bore the interior of the billet.
I do this in steps, as brass tends to 'catch' easily on the cutting piece, and tends to slip from the chuck.
Using a two-flute milling end as a cutting tool, I bore the interior of the billet to 30mm.
This hole is temporary, and the movement's outer profile will be turned so that it has a snug and precise seating in the case.
The side of the billet is turned perpendicular to the face we just cleaned. This is because the billet is never perfectly concentric, and in a 3-jaw chuck the work tends to be off center.
I start to part the piece which is 13mm thick. This is thicker than the case, but is done to accomodate machining operations.
Once the case center has been parted off, it is turned around and the other (back) side is faced off to achieve parallel faces.
A smooth finish is made in order to receive correct readings from the micrometer.
The case-middle billet is finished.
Measurements are taken, and coordinates are etched into the billet (here the interior of the lugs, and the outermost diameter of the case).
The billot is placed in the lathe, and the interior diamter is turned.
The movement seat is opened to diameter with one cutting tool.
The geometry of the cutting bit is changed to get at the interior angle for the movement seat.
The movement base plate is checked for snug fitting.
Next the diameter of the bezel seating is turned to size.
The next steps (after coordinate holes) is to turn the front and back bezel threads.
The case middle is then placed on the jig boring machine, and coordinate holes are drilled.
Locating where the holes will be drilled.
First hole is drilled.
How the hole looks after drilled and checked for location with the centering microscope.
Final holes drilled. Outer case holes will be drilled after thread has been applied to case top and bottom.
In order to cut the case sides I have to center a separte cross trable and rotary table onto the jig borer. A rough centering is done with a cone taper fixed on the spindle.
The rotary table base is centered to the spindle.
Then, the holding chuck has to be fitted onto the rotary table, and also centered, so that when the rotary table is turned, the chuck is concentric in its turns.
With the centering microscope I check that the case is fitted square to the cross table.
The upper cross table is then moved to coordinates so that an arc can be milled from the side of the case.
A test cut is made. Here the arc connecting the round body to the lugs is cut.
Two lug curves have been cut (the case is turned 180 degrees for this cut).
After returning the case to the first position, the coordinates are shifted to mill the other arcs.
Finishing the four arcs of the case side.
The case has to be recentered to mill out the 'wings' that are left on the case sides.
Checking that the case is still centered, as the case (and cross table itself) tends to come out of center due to later forces when milling.
Milling off the sides of the case.
Case sides milled.
Re-centering the case. I was not happy with the result of two of the 4 case arcs.
Repositioning the case to touch up the two arcs.
Finished touching up the arcs. Next are the interior areas of the lugs.