Intro: Prototype Slot Screws
I make my living making things. By day I make things for other people as a master tool & die maker, prototype machinist, chief cook and bottle washer. After work I make things for fun for me. This Instructable is about one of the "making things for other people" jobs. Since I use this picture as my profile picture, doing this Instructable was almost a requirement. I apologize for the poor quality of some of the photos in this; I had recently gotten a new camera and this was a project I wanted to do as an Instructable, but I didn't take the time to review, edit, and reshoot.
Step 1: First, a Little Lathe Work.
Starting with 3/8" round brass rod and my old Southbend lathe, we turn the shank of the screw. I took three passes.
Step 2: Cutting Threads.
Cutting threads this small on a lathe can be tricky; a moments inattention and it's gone! Fortunately, at this point, I can easily make a new one without backtracking; I've already set this up to make multiple screws.
Step 3: Parting Off.
The last step on the lathe is parting off. This also leaves us with the head at the correct dimension.
Step 4: Cutting the Straight Sides.
I used a vice in a vice for this because the big mill vice jaws edges are too worn to grip tiny parts.
There was not much material to hang on to for the second cut!
Step 5: The Special Setup.
Now we get to the interesting part! How do we hold the screw so we can cut the angled sides? We use soft jaws! Replacing the hard jaws on the mill vice with soft aluminum jaws lets us cut a special pocket to hold the screw in just the right way. This is probably one of the simplest ways to create a milling fixture.
Step 6: Cutting the Angled Sides.
I set this up on my CNC, mostly because I could. It was overkill for a dozen screws. But it was not being used for anything at the moment, so...
Step 7: Inspection and Done!
The optical comparator is the tool to use when measuring features you can't get to easily.