A repair job to a wrench called for a slotted axle screw to be fabricated for a missing original, a piece of rod was threaded on one end and marked for the cutoff length. A simple slot would suffice at the cutoff end, but it being just a small headless set screw meant that an accurately centered slot was demanded else proper installation could be compromised. This is how that problem was solved with typical shop hand tools.
On a piece of scrap wood, make a straight centerline, and mark 3 equal spaces. The distance isn't really critical, so make it comfortable for handling.
Bore a hole in the center for a friction fit of the workpiece, In this case it was a 1/4” [6.4mm] diameter rod. Flanking it, drive in two brads, headless if available, but a smooth shank and same diameter is what's desired. Drive them plumb and straight and also on their mark.
It's preferable to clamp this fixture in a vise, but use whatever means available to hold it steady whilst gently hack sawing away. An 18 tooth/ inch blade easily cut a slot about 1/8” [3.2mm] deep, plenty for the task to be. The action is simple; the blade is guided on the inside edges of the brads and spans the work, automatically giving a centered cut.
Job done, setscrew neatly and precisely installed. For even finer work, a jeweler’s saw can be employed to slot the smallest of screws.