CNC Brand Profile

UNISIG and the American Machine Built to Drill Deep and Straight

Most machining problems are about removing metal from the outside of a part. Deep-hole drilling is the opposite problem. You are cutting several feet into solid stock through a hole barely wider than the drill, blind, with no way to see the tool, flushing chips back out through that same narrow channel, and the whole time the hole is trying to wander off line. Drift a few thousandths over a few inches and you can live with it. Drift over ten feet and the part is scrap. This is a job a standard machining center simply cannot do, and it is the only job UNISIG builds machines for.

That single focus is the whole story of the brand. UNISIG does not make a little of everything. It makes the machine that drills a deep hole and keeps it straight, and it has spent more than forty years making only that. For a used-machine buyer, understanding what that specialization buys you, and what to check before you buy it, is the difference between a machine that opens a new line of work and one that sits idle.

A Specialist From Day One

UNISIG was founded in 1981 to bring deep-hole drilling machines, tooling, and service to the U.S. market, started in Elgin, Illinois, by the Swiss Industrial Company, known as SIG, together with the American firm United Technical. The Swiss connection is worth noting, because deep-hole drilling is a discipline European builders had long refined, and UNISIG grew into a machine built and supported in the United States.

In 1995 UNISIG was acquired by Entrust Manufacturing Technologies and relocated to the Milwaukee area, in Menomonee Falls, Wisconsin, where it is based today. Entrust, founded in 1973, gives UNISIG the manufacturing depth of a larger parent while the brand stays pointed at one thing. UNISIG later added a German operation, UNISIG GmbH, founded in 2011 to serve European customers. Through every ownership change, the mission never widened: deep holes, done straight.

What Deep-Hole Drilling Actually Takes

Deep-hole drilling is usually defined as a hole with a depth-to-diameter ratio past about 10 to 1, and UNISIG builds machines that run far beyond that. Getting there takes purpose-built processes that a general machine cannot fake.

Gundrilling uses a single-flute tool with high-pressure coolant fed through the tool to push chips back along a V-shaped flute, ideal for smaller diameters and very high length-to-diameter ratios. BTA drilling, named for the Boring and Trepanning Association, flushes coolant around the outside of the tool and pulls chips back through the center, moving metal faster at larger diameters. Trepanning cuts an annular groove and leaves a solid core instead of turning the whole hole into chips, which saves material and energy on big bores. Skiving and roller burnishing finish a bore to a fine surface in one pass, the process behind hydraulic cylinder tubes. UNISIG builds machines for all of these, plus the tooling and the automation to feed them, which is why a shop buys the brand to open a capability it did not have before.

Two problems make deep-hole drilling hard, and both are why the machine matters as much as the drill. The first is straightness. A long tool wants to wander, so the process leans on a precise starting bushing, rigid tool guidance, and a machine stiff enough that the drill tracks true over feet of travel instead of drifting off line. The second is chip evacuation. You are cutting blind at the bottom of a narrow hole, and if the chips do not clear, they pack, jam, and can break the tool or ruin the bore. That is why high-pressure through-tool or around-tool coolant is not an accessory on these machines, it is the heart of the process. A deep-hole machine is really a coolant and guidance system with a drill attached, and a builder that has spent forty years on exactly that problem is what you are paying for.

A machining center removes metal from a part you can see. A deep-hole machine cuts blind, feet into solid stock, and has to come out the other end straight. Those are not the same skill, and they are not the same machine.

The Machine as a System, Not Just a Drill

One thing that separates UNISIG from a shop bolting a gundrill onto an existing machine is that it builds the whole process as a system. The machine, the tooling, the high-pressure coolant, the chip handling, and the automation are engineered together, so the deep hole comes out to spec without a shop having to invent the process from scratch.

That shows up in a few ways. UNISIG builds dedicated deep-hole machines for gundrilling and BTA work, and it also builds universal deep-hole machining centers that combine drilling with additional operations so a long part can be drilled, bored, and finished without moving to another machine and losing the reference. It builds the tooling and drill heads that match its machines, because in deep-hole work the tool and the machine are a matched pair, not separate purchases. And it builds automation, from part handling to full turnkey cells, for shops drilling the same family of parts in volume.

For a buyer, that systems approach is the value and the caution at once. The value is that a UNISIG machine arrives as a proven process, not a science project. The caution is that the tooling and coolant setup are part of what makes it work, so a used machine stripped of its tooling package is a very different purchase than one that comes complete. When you evaluate a used UNISIG, you are evaluating a system, not just a spindle and a bed.

Where UNISIG Machines Earn Their Keep

The industries that need deep, straight holes are some of the most demanding in manufacturing. In aerospace, that means landing gear, actuators, and structural components where a deep bore has to hold both straightness and finish. In energy and oil and gas, it means long shafts, downhole tools, and components that see high pressure. Defense work runs to gun barrels and ordnance, the original home of gundrilling. Medical shops drill bone screws and surgical instruments. Mold and die shops drill cooling lines deep into tool steel, where straight, well-placed water lines decide cycle time and part quality. Hydraulic cylinder makers rely on skiving and burnishing for the bore finish.

What these have in common is that the deep hole is not a secondary feature. It is the reason the part exists, or the feature that makes or breaks it. That is why deep-hole shops treat the machine as a core capability, and why a used deep-hole machine, matched to the right work, can be a fast path into high-value jobs that most shops cannot bid.

The Used-Market Angle

Deep-hole machines are a niche, and that cuts both ways for a buyer. New UNISIG machines are a serious capital purchase, so a well-kept used one can open the capability at a fraction of the cost. Because these machines are specialized, fewer of them trade hands, so when the right one comes up, matched to your diameter and depth range, it is worth moving on.

The flip side is that a deep-hole machine is only valuable if it matches the work. Diameter range, maximum depth, and the process it is set up for, gundrilling versus BTA versus skiving, are not interchangeable, so the machine has to fit the parts you intend to run. Tooling and coolant systems are a real part of the value, because high-pressure through-tool coolant and the right drill heads are essential to the process. A used UNISIG that comes with its tooling package, in the size range you need, is worth far more to you than a cheaper machine that almost fits.

There is a strategic angle here that goes beyond the price of the iron. Many shops that need deep holes have been sending that work out for years, paying an outside vendor and waiting in that vendor's queue on every job. Bringing the process in-house on a used deep-hole machine changes the math. It pulls a bottleneck operation back under your own roof, protects the lead time on the whole part, and lets you bid complete jobs you used to split with a subcontractor. For a shop already turning down or outsourcing deep-hole work, a used UNISIG is not just a machine purchase, it is a decision to own a capability and the margin that comes with it. That is a different calculation than replacing a machine you already run, and it often makes a used deep-hole machine easier to justify than its sticker suggests, because the machine is not really a cost, it is the thing that lets you keep the whole job and the margin attached to it.

What to Check on a Used UNISIG

Size and depth range. Confirm the machine's diameter and maximum drilling depth actually match your parts. This is the first gate. A machine outside your range is the wrong machine at any price.

Process match. Know whether it is set up for gundrilling, BTA, trepanning, or skiving. These are not casually converted from one to another.

Coolant system. High-pressure through-tool coolant is central to deep-hole drilling. Check pump condition, pressure, filtration, and the seals. A weak coolant system will not clear chips, and chip evacuation is the whole battle.

Tooling included. Confirm what drill heads, boring bars, and tooling come with the machine. Deep-hole tooling is expensive and process-specific, so an included package is significant value.

Control and support. Identify the control and confirm parts and service are available, and ask whether UNISIG still supports that generation. A specialist machine leans harder on builder support than a common VMC does.

Resell CNC Take

A deep-hole machine is the rare piece of used iron that can pay for itself by letting a shop bid work nobody down the street can touch. But it only works if the machine fits the job. We match a used UNISIG to a buyer by diameter, depth, and process first, then condition, then tooling, because the cheapest deep-hole machine that does not fit your parts is worthless, and the right one is a new revenue line. If you are eyeing deep-hole work, tell us the parts you want to run and we will tell you whether a machine actually fits before you spend a dollar.

Frequently Asked Questions

What is UNISIG known for?

UNISIG is an American deep-hole drilling specialist based in Menomonee Falls, Wisconsin. It builds gundrilling, BTA, trepanning, and skiving machines, plus tooling and automation, for holes from under 1 mm to about 1 meter in diameter and depths past 65 feet, serving aerospace, energy, defense, medical, and mold and die work.

When was UNISIG founded?

UNISIG was founded in 1981 in Elgin, Illinois, by the Swiss Industrial Company (SIG) and United Technical to serve the U.S. deep-hole drilling market. It was acquired by Entrust Manufacturing Technologies in 1995 and moved to the Milwaukee area. A German operation, UNISIG GmbH, was founded in 2011.

What is the difference between gundrilling and BTA drilling?

Gundrilling uses a single-flute tool with high-pressure coolant fed through the tool, best for smaller diameters and very high depth-to-diameter ratios. BTA drilling flushes coolant around the outside of the tool and pulls chips back through the center, removing metal faster at larger diameters. UNISIG builds machines for both.

What industries use UNISIG machines?

Aerospace, energy, oil and gas, military and defense, automotive, hydraulics, medical, and mold and die. The common thread is a deep, straight hole that a standard machining center cannot produce, such as gun barrels, hydraulic cylinders, landing gear, and cooling lines in injection molds.

Is a used deep-hole drilling machine worth buying?

It can be, if the machine matches your work. New deep-hole machines are a major capital purchase, so a well-kept used one can open a high-value capability for far less. The key is matching diameter, depth, and process to the parts you plan to run, and confirming the coolant system and tooling are in good shape.

How deep can UNISIG machines drill?

UNISIG machines handle holes from under 1 mm to roughly 1 meter in diameter, at depths ranging from a few inches to more than 65 feet, depending on the model and process. The right machine depends on the specific diameter and depth of the parts you need to produce.