Quote:
Originally Posted by Cory
If you are looking to be able to tap through holes without stopping and reversing the tap to break off the chip, look into spiral point taps. They will drive the chip ahead of the tap and should tap any reasonably ductile material in one shot without reversing. They are also no harder to align than a standard hand tap. |
Seconded. At my employer, this is they type that engineers (like myself,), fabricators, and maintenance workers use. They're great for both hand use and machine use (I've used them at "slow" speeds using cordless drill, drill press, and lathe with good results).
As for brands (at least the ones I've used), Hertel ones aren't too bad (I've grenaded a few but I was abusing them a bit) and the few Kennametal ones I've used at work were awesome (same abuse as the Hertels, didn't break). Irwin ones are pretty good as "retail" brands go (their tap handles not so much, the one I bought my father in law cracked on the first use). Craftsman ones are good as well. Harbor Freight ones (never used at work, personal work only) aren't so good but for aluminum and mild (unwelded) steel are OK if you're nice to them. Avoid the cheapest ones though, as they might as well be made of silly putty. The mid-grade and upper tier ones are worth the extra money.
Somewhat relevant trick of mine: if there is trouble clamping the part in the drill press vice, the tap is slipping in the drill chuck, or if you're tapping a blind hole, use a drill press/lathe to start the tap (to make sure it's straight), and once the tap has started, back out the tap and move the part to the bench vice and finish it by hand. I had a weird foot for a jig clamp I was fabricating for a work project last week that drilled fine on the drill press but wasn't agreeing with the tap (deep hole, M8 tap, Jacobs chuck was slipping) and this trick was how I salvaged the part.
TL,DR: Spiral point taps are awesome!