I wrote a dissertation length response to this yesterday, but, as usual, had a hard time holding back the snark. I try not post on the internet on those days.
Most switches are so simple, one good look at one is all it takes to get the concept. I can describe it in its basic form, but pictures might be easier and I'm not including those.
A basic bottom switch is composed of a body, lock ring, spring, post, insulator (or two), and a button. That's it. The body is threaded to fit the tube. The inside or outside is threaded for the lock ring depending on the design. The post and button thread together in the center sandwiching, from the top, an insulator, body, lock ring and spring. The current should pass from the post, through the walls of the hole in the body in which it passes, through the body to the threaded junction with the tube. Current should not flow through the spring.
The fun part as a designer is making all those parts function smoothly together, have as little resistance as possible and take up as little vertical space as possible.
Some switches will have more parts. Some use magnets in place of springs. Most are taller than neccesary. Using left hand threads on the lock ring is a good idea. I use delrin for my insulators and design them so they are captured. Other people use o-rings set into a face groove. The insulators only job is to keep the post away from the battery when the button isn't being pressed.
Bear Brass mods made a perfect example of how not to make a switch, so searching for that will bring up lots of discussions. (They insulated the post. Current had to pass down the post, through the button, up the spring and back to the body of the switch. There was enough resistance there to heat up the button pretty good.)
The lock ring has a smaller ID than the OD of the button. When threaded out, it prevents movement.
As a student machinist, there is plenty of fun stuff here as far as making a bunch of concentric, threaded parts as well as left hand threads. Nice part, though, is since you are making all the parts, you can pick whatever thread pitch you like and turn the parts to fit each other. No need to gage anything, really.
Sorry for the delayed response, but I hope there is enough here to get the concept down.
