Drilling and tapping a hole in steel isn't very complicated. The center punch has to be exactly located at the intersection of the layout lines and to facilitate this I use a sharp pointed center punch that is moved down the first scribed line until it "falls" into the cross line. A tap w/ the hammer and the "dimple" is centered.
A small drill w/ a dia that's larger than the web of the tap drill is run through. The reason for the small drill is that it's flexible and will move over if the spindle is slightly off....it is then aligned. Some use a center drill which doesn't flex and is used for workpieces that are clamped in machines like the milling machine . A hole can be mislocated w/ a center drill, especially when drilling in wood.
Proper spindle speeds are also necessary ...many drill presses don't have high enough spindle speeds or the operator isn't knowledgeable as to drilling spindle speeds.
After the tap drill, a ctsk is used and then I chuck the lubed tap in the spindle, center it in the hole and bring up, turn the spindle on and then off and while it's "coasting" it's engaged into the hole and after a few threads are cut it stops and the tap is unchucked and the remainder of the hole is tapped by hand w/ the bbl clamped in a bench vise. Some might prefer to use a tap wrench located by the spindle and turned by hand.
After the hole is tapped w/o a ctsk for a White Lightning, , a ctsk is then used for the angled flange seal...going deeper w/ the ctsk yields a longer TH land and a shallower ctsk results in a shorter TH land. The ctsk depth is very important because if not deep enough, the TH land could be very short and might end up being a "feather edge" which would blow out.
After drilling tens of thousands of holes as a tool and diemaker, the above procedure was proven to be an accurate way to locate and drill holes in steel.....Fred
