Fast spiral tap speeds

[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.

[mentorDon]

The drill/tap combo (DRAP) is best used on a CNC machine. The amount of material thickness must be less than the drill length of your tap of course. No blind holes! And for your case, the inside diameter of the pipe must be larger than the combined length of the cutting portion of the drap. The machine is programmed at a surface speed for drilling depending upon material and diameter. A feedrate is calculated to match material and speed. At a programmed 'z' depth after material brake through, the spindle speed is reduced and a new feed rate to match the rpm and pitch of the thread. After reaching the lower 'z' setpoint, the spindle is reversed and the tapping portion is fed out using the previous feedrate. Once the tool is clear, spindle direction is reset to clockwise, rpm increased, and moved to the next location. There are special tapping heads with springs to allow for inaccuracies of rpm and feedrates.

[Foster]

Thanks. After I did the tap the old way, I did some trial runs on some scrap tubing. Key thing is to be able to have slow speed for the tap and being able to reverse. Since the drill press I have had slow speeds I was able to get it down to the suggested 30 RPM.

On the plus side, they are much easier to use as a hand tap since the initial bit helps keep the tap straight in the hole.