Drilling very small, very deep holes is one of the toughest challenges on the shop floor.

When you’re working with holes that are under 2 to 3 millimeters in diameter and drilling to depths of up to 30xD, issues such as chip evacuation, heat and hole quality all become much harder to control.

That’s the niche that cutting tool manufacturer OSG is targeting with its ADO-Micro and AD-Micro carbide micro drills, which are designed to produce small-diameter holes with high accuracy and reliable performance.

OSG product engineer Jaime Dimayuga says the drills are well-suited for precision machining in a broad spectrum of materials including carbon and stainless steels, cast iron, aluminum alloys, titanium alloys and heat-resistant alloys.

ADO-Micro and AD-Micro: Two Paths to High-Precision, Small-Hole Machining

The ADO-Micro series, which was introduced in 2019, “provides coolant-through high-performance carbide drilling for small diameters, and it goes all the way from very short 2xD all the way up to 30xD,” Dimayuga says.

“For drilling very deep holes without pecking, you need internal coolant. Otherwise, you can’t evacuate the chips,” he says.

The newer AD-Micro series, introduced in 2025, is a non-coolant-through micro drill, offered in 4xD and 10xD lengths, that features optimized cutting-edge geometry and flute design to improve chip evacuation when using external coolant.

“With AD-Micro, we do 10 micron increments from .5 mm all the way up to 3 mm in both 4xD and 10xD, which means it’s a huge offering, around 502 items, for just those two lists,” he says.

Dimayuga says that while on the surface ADO-Micro and AD-Micro may appear to be coolant-through and non-coolant-through versions of the same product, their geometries are very different.

“ADO-Micro has essentially a full margin, 1xD, to help aid with the entry of the drill, but then past that, it also has a gap in the margin that allows the coolant and chips to flow through and get flushed through the flutes and out of the hole,” Dimayuga says.

Fighting Micro Sludge: Why Coolant and Geometry Matter

One of the biggest differences between micro drilling and standard-size drilling is how small chips behave in the presence of coolant.

“When the chips are very small, they’ll start to interact differently with the coolant on the level of flow dynamics, and that can create what’s called micro sludge,” Dimayuga says. “This is a different type of chip clogging than what we normally see with standard-size drilling.”

The unique geometry of the ADO-Micro drill, combined with the coolant-through component, is what combats micro sludge.

“This not only allows the coolant to be directly delivered to the cutting edge, which is best for both lubrication and for heat mitigation, but the coolant is now running from the end point of the drill and up out of the hole through the flutes, which aids in chip evacuation,” he says.

Pecking, Tool Life and Process Choices

When using the AD-Micro, the right pecking technique is important, according to Dimayuga.

Chip-break pecking—where the drill advances a short distance, retracts slightly while still spinning, and then goes back in—is what OSG recommends. It gives the chips a chance to clear, lets coolant reach the cutting zone from outside and keeps the tool from running too hot.

“This type of pecking will save you tool life, and the quality of your hole will be that much better,” he says.

Full retract pecking, where the drill pulls completely out of the hole between pecks, should be used as a last resort. “You should only use that when you just can’t get the chips to break and you need the chips out of the hole, because that’s going to give you your longest cycle time and your worst tool life,” Dimayuga says.

Setup, Coolant Pressure and Filtration: Details That Matter

For shops that are running either the ADO-Micro or AD-Micro for the first time, Dimayuga says some basic setup discipline is what can help make or break tool life.

“One of the biggest issues with micro drilling is obviously that runout is tantamount, so you want to minimize runout as best as you can,” he says.

With the coolant-through ADO-Micro drill, both pressure and filtration are key.

“We find that the best coolant pressure is somewhere around 500 psi,” he says. “We’ve tried 1,000 psi, but there are some occasions where 1,000 psi actually has more trouble getting into the coolant holes, given how small they are.”

“The other thing you need to keep track of with coolant-through drills is making sure that your coolant filters are down to between 3 to 5 microns,” Dimayuga adds. “If your filters aren’t fine enough, now your chips are everywhere and that can be a nightmare.”

From Molds to Medical to Data Centers: Where Micro Drills Show Up

Small-diameter drilling is relevant to a variety of applications and industries, Dimayuga says, “including medical, aerospace and automotive, as well as die and mold and any job that requires holes that are under 2 or 3 millimeters.”

In the injection mold word, for example, shops rely on very small, very deep holes to create effective coolant channels.

Micro drilling is also important for semiconductor manufacturing in the U.S., he says, because micro tools are required to make the tight tolerance components that hold and support chips through various stages of production.

“While we don’t see too much of this type of manufacturing in the U.S. right now, it is a growing market because of the increase in data centers,” he says.

For shops that are facing an uptick in work that involves drilling small-diameter, deep holes, choosing the right micro drill matters. OSG’s ADO-Micro and AD-Micro product lines can help manufacturers tighten up tool life, protect hole quality and keep cycle times in check when they’re drilling at micro scale.

Video: Attain Your Need for Speed with OSG’s ADO-Micro Drill