Custom License Plate Screws

After finishing the rotary broach, and having a 5/32" broach ready to go (the size of hex for my other 1/4"-20 socket machine screws), I was ready to rumble on my machine screws.

I first tried to make it head first so I could punch the hex hole in it.

While this worked in getting the basic profile, getting the thread in there would have absolutely wasted brass material.  Additionally, once threaded, and parted, I had a bad bolt - it didn't even seat into the washer, indicating that I had the angle completely off that I'd measured.  I could not check the fit of the screw while in the part was still in the lathe.  (The angle was measured as a 90-degree bevel.  Apparently, even though I did my best, I did not get it proper.)

I did this twice before I realized I was wasting more material because I could not test it, and concentric surface on the other side was inconsequential.

Third try is the charm.  I used some aluminum and realized that all I need to do is get the angle less than the washer so that the upper edge would seat.  I just wanted it close enough.  Truth be told, it is nearly half way between 45 and 60 degrees, but since 60 degrees would have given me the outside seat, I went with that with the tool squared up.

On my next try, I opted to reverse the construction - turn the outside diameter (0.600", then cut the 60-degree, large chamfer for the bottom of the head to the 1/4" diameter, then thread it on).

Once that was ready, it was time to part it off.

Now, I have two bolts, with no way to grip them yet.  I used a chunk of 9/16 aluminum bar stock and drilled and tapped it to 1/4"-20.  I then cut a number of slots into it so that I could chuck this little tiny bar into the lathe to get "close enough" on the concentric nature of these bolts.

In the previous photos, I had not yet cut two other slots (not all the way through) on the chucking nut in order to properly grip the screws.  Set in the chuck after the cuts, I proceeded to drill a 5/32" hole as a start, re-chamfer the entry point on the drill, then broach it through.

And that is now two license plate bolts complete.  I need to fabricate the light bracket and install the lower plate before I can install these, but two more parts have been completed.