We’ve had a three-pack of Irwin’s Unibit step drills sitting around the shop for a few days, and today we got the chance to put them to use — in this case creating a 3/4″ hole in a steel bracket we were fabricating.
If you’re not already familiar with step drills, they’re quite simple: They’re essentially of a cylindrical pyramid shape and alow you drill a number of different sized holes with a single bit. As the drill cuts through the material it “steps” to each new step of the pyramid, enlarging the hole that much more. When you’ve reached the desired size, you just stop at that step and you’re done.
The kit we have includes three bits: one which handles hole sizes from 1/8″ through 1/2″, one that handles 1/4″ through 3/4″ and one that handles 3/16″ through 1/2″. Each one features quite a few steps, so carrying around this one three-piece set is almost like carrying around a huge set of 19 different drills.
The Unibits feature Irwin’s SpeedPoint tip which is a two-flute drill on the bit’s tip which quickly cuts material to create the initial hole — Irwin claims up to 6X faster than their original Unibit step drills. The steps themselves cut with a single flute — a large notch cut into the “pyramid” all the way down the bit. Fewer flutes, by the way, makes for a more aggressive drill, and a single flute drill is the most aggressive of all.
In our use, we were very happy with the Unibits. They cut quickly and leave a surprisingly clean hole considering the aggressiveness of their design. Of course sometimes a more aggressive bit can actually lead to a cleaner hole as users are less likely to “bear down” hard on the bit creating a punch-through and, hence, a distortion of the drilled hole. The Unibits cut so easily that they required little pressure to generate satisfactory progress through the material.
Though the sizes are clearly marked and it’s easy to select and drill a particular size of hole, it’s also handy using the Unibits in fabrication situations where you’re not sure exactly how large a hole you need. For example, we were creating a hanging bracket and wanted enough room for a particular fastener to fit, and it was very easy to just run the Unibit through until we reached a size that looked like it’d fit.
Irwin recommends the Unibit for drilling materials up to 1/8″ thick. (Larger materials won’t fit over the steps.) One of our brackets was 1/8″ thick and we had no problems at all.
Irwin carries quite a line of Unibits ranging widely in size. Some are self-starting (with the SpeedPoint tip) and some (especially the larger ones) are used just to expand holes. Most are high-speed steel, and some feature titanium coatings.
Unibits are available at most hardware and home improvement stores and start at around $12.