How do they grind those teeny-weeny taps anyway?

The work is done on thread grinders, with extremely fine and hard grinding wheels. The wheel description is of necessity to maintain thread form. While I've never operated a thread grinder (I have ground for a living, but on other machine types), it's my understanding that they use oil for coolant, which also lubricates the wheel and cut. You might take note that the ends of taps are made such that they operate as centers, in most cases, male, not female. For bottoming taps, it's likely they grind off the center once the tap is ground to configuration.

Harold

When I was young and with good eyes I use to grind thread gages,some as small as 0-80 !! Boy those were the days now I can"t even see a 0-80 screw. Ray Mueller

Only based on some photos which I have seen, but it seems that the wheel is form-dressed to produce multiple threads side by side, which suggests that the wheel must be advanced in sync with the rotation of the workpiece -- in other words, not your usual surface grinder, but rather a specialized machine.

Enjoy, DoN.

My understanding was that the thread on th wheel is formed by rolling with a hardened roller with the thread form on its surface. I think the theory is that the grains are both cracked and broken off the wheel with very little damage to the forming roller. I could also be hopelessly wrong.

Mark Rand RTFM

No No They are dressed with diamonds. The wheels are VERY hard in order to hold the form.Ray Mueller

Crush form rolling is a common practice used on precision grinders, including centerless grinders. For grinding threads, however, the form is dressed by diamonds that are mounted permanently on the grinding wheel head. The diamonds are generally adjustable for thread form, which changes constantly as the pitch of the thread changes. Compensation for the helix angle of the thread is accomplished by tilting the wheel head, which in turn must have the thread form altered slightly to maintain the proper thread form angle. Crush form rolling would not work very well in this instance because of the ultra-critical finish and form that is required.

Harold