Fast spiral tap speeds

[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.

[ratdude747]

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!

[DonRotolo]

Although the OP decided to solve the problem by using a different tool, the spiral point tap he was given appears to be the same as what Cory mentions.

Regardless of the RPM, it is critical that he have a way of reversing (or at least stopping) the tap before the tip hits anything solid. So if he doesn't have a Tapmatic head, slow is the answer. But a good tap can run at several hundred RPM, maybe 1200, depending on the details (a harder job needs slower speeds)

Tapping with a hand drill will break the tap with even the slightest movement. Don't even try.

[Foster]

They look more like a spiral drill bit with a tap at the middle rather than what Cory posted. Best picture I could find was this one



I found a site that had the speed calculations I was really after

For mild steel pipe and the 1/4" size hole/tap I needed to go ~30 RPM.

After I did the project with a hand tap, I did try the drill/tap just as a learning point for me. In a press, it was easy peasey to drill the hole and then tap right behind it at a slow speed. Needing to be able to reverse is a key thing.

Unlikely I would have been successful out in the yard doing this with a hand drill.

And if I could afford a Tapmatic head at $350, I'd be lots smarter than I am and would have done this before I sank the pipe into 350lbs of concrete.

Thanks again to all that replied.

[Cory]

Oh, that's just an integrated drill/tap. Totally different than what I thought you had.

I thought you had one of these:



The one you have should in theory not present any problem with following the hole since it's also making the hole (though it could easily end up with both being non-perpendicular to the surface). The one above is much more difficult to align perpendicular to the hole since it has almost no lead in and the flutes are more "aggressive" than a standard hand tap.