A convex hole?

[Bill C.]

I want to create a hole in steel, aluminum, and brass like those in the center of the screws in the attached picture. I've tried grinding an HSS tool to bore such a hole on my lathe but I can't seem to get close. I wonder if there is a bit on the market that will leave a convex bottom in a hole like this. Any direction will be appreciated.

I found your photo source, a 6-32 screw. Something that small likely was cold forged. What you are trying to do would be on the small scale or micro-machining. Definitely tamper resistant. Interesting design.

 

[Marco Bernardini]

If your goal is to make a tamper resistant screw, a tricky idea is to make it left hand, too.

 

[ddmunroe]

Who ever makes these screws has cnc tooling and machines, I would consider making them only if I could not buy them
With HSS profile tools labouriously made. Perhaps using multiple tool bit profiles and LOTS of polishing.

 

[Cactus Farmer]

I made a screw with a convex center once, the take down screw for a Starr percussion revolver. I did it in two steps, inside and then the outer cut. Then the hemisphere was slotted to look like a screw head. Knurled the outside rim to allow a grip. I'll have a pic this PM, the pistol is in the vault in town. You might be able to Starr. It's a double action 44 made before the Civil War. Heavy but very powerful.