In my shop class more than 50 years ago, now, we had to use a tap and die set to thread holes in a small set of parallel clamps we made with hand tools from scratch. Use a Tapered tap to start the threads. The taper helps you center the tap in the hole. The hole should be drilled to Tap size- use a chart to get the correct size. As Keith notes, of you get that tap hole drilled at 90 degrees, the tapered tap will follow at the same angle, unless you horse it. Don't!
The technique you should use with these small taps is to turn the tap so it cuts 1/3 of the circumference. Then stop, and back the tap up 1/8 turn to break lose the chips and push them into the long smooth flutes of the tap, so that they will flow away from the cutting edges of the tap.
The same technique is also used when using a die to thread a piece of round stock.
Use plenty of Tap OIL- it different from other oils, and made specially for this kind of work. Buy it at your hardware store. Remove the tap from any blind hole( Ie. a hole with a bottom) and brush the chips out of the flutes, and the teeth of the tap often. Then, re-oil the tap before running it back down into the threads you have already cut.
I buy two tapered taps for each size, and then grind down one of them to remove the tapered section so I can use it as a " BOTTOMING TAP". IN A BLIND HOLE, once the tapered tap goes to the bottom, I change over to my bottoming tap, and finish cutting the full threads down to the bottom of the hole. Mark the depth of the hole on the tap, so you don't break the tap trying to turn more threads when you have already hit bottom! Taps are very hard, and very sharp, but they are also very brittle. :shocked2: :idunno: :surrender:
Thank you for not asking me how I know about that last piece of advice. :shocked2: :bow: :thumbsup: :hatsoff:
Oh, you can order "bottoming taps from suppliers, but the cost is so much higher than that of the tapered taps that it doesn't make a lot of sense to spend your money for them. All you need is a grinder to shorten a tapered tap to make that bottoming tap. Only if you have a long, deep hole to thread and need a long shank on the tap would I ever consider buying a bottoming tap. Even then, it probably would be cheaper to find a friendly welder and just weld a longer rod to the existing shank on an inexpensive tapered tap. :hmm: :surrender: :thumbsup:
Did I tell you I am basically genetically wired to being "frugal", as my father used to say?? :grin:
