If you walk into a high-end tool room or a heavy-duty repair shop, you're almost guaranteed to see a devlieg boring mill standing like a silent sentinel in the corner. These machines, specifically the ones often referred to as "Jigmils," have a reputation that most modern equipment manufacturers would kill for. They aren't just pieces of cast iron; they are symbols of a time when precision was earned through incredible engineering rather than just slapping a high-resolution encoder on a cheap frame.
It's funny because, in an age where everyone is obsessed with the latest 5-axis CNC machines and lightning-fast rapids, the DeVlieg remains a staple. You'll see guys who have been machining for forty years refuse to let go of their 3H or 4K Jigmils. There's a reason for that. It's not just nostalgia—it's about the fact that these machines can hold tolerances that make some modern mills look like toys.
What Makes a DeVlieg a "Jigmil"?
The term "Jigmil" wasn't just a catchy branding exercise by Charles DeVlieg back in the day. It actually described a hybrid capability. Traditionally, you had jig borers for extreme precision and boring mills for heavy metal removal. DeVlieg decided he wanted both. He built a machine that had the rigidity of a horizontal boring mill but the accuracy of a jig borer.
The secret sauce was in the construction. These machines were built on massive, hand-scraped box ways. If you've ever tried to maintain a machine, you know that linear guides are great for speed, but for dampening vibration and staying true under a heavy cut, nothing beats a well-oiled box way. When you're running a large boring bar deep into a workpiece, you need that mass. A devlieg boring mill doesn't chatter; it just eats.
Another thing that set them apart was the "Spiramatic" spindle. The way these spindles were designed allowed for incredibly fine adjustments. Back before we had digital readouts (DROs) that could tell you exactly where you were to the fourth decimal place, DeVlieg users were using end measures and micrometer heads to position the table and spindle head. The machine was designed to be inherently accurate from the factory, not just "corrected" by software.
The Spindle and the Tooling System
One of the coolest features—and something people still talk about—is the FlashChange tooling system. If you've ever fumbled with a drawbar while trying to hold a heavy tool, you'll appreciate this. The FlashChange system allowed for quick, repeatable tool changes that were surprisingly accurate for a manual setup.
The spindle itself is usually the heart of the machine's value. Whether it's a 3-inch or a 4-inch bar, the way the spindle extends and retracts is buttery smooth. It allows for deep-hole boring with minimal deflection. I've talked to shop owners who use their devlieg boring mill specifically for gearbox housings where the bores on opposite sides have to be perfectly aligned. You can bore one side, index the table 180 degrees, and hit the other side with frightening precision.
The "K" Series vs. The "H" Series
If you're looking at getting one of these on the used market, you'll probably run into the H and K designations. Generally speaking, the K-series is the later, more "modern" version (if you can call a machine from the 70s or 80s modern). They tend to have higher spindle speeds and some updated electronics.
The H-series machines are the old workhorses. They might look a bit more "classic," but don't let the dated paint jobs fool you. If the ways aren't scored and the spindle hasn't been crashed, an H-series machine will still out-perform most mid-range new mills in a boring contest. The "K" models often featured some of the early Diatrol systems—DeVlieg's early foray into automated positioning—which were honestly way ahead of their time.
Why CNC Haven't Killed the Manual DeVlieg
You'd think that with the rise of CNC horizontal machining centers, the manual devlieg boring mill would be extinct by now. But it's actually the opposite in many specialized industries.
Think about a repair shop that handles massive engine blocks or custom one-off parts for the mining industry. Programming a full CNC routine for a single part can sometimes take longer than just "walking up" to a DeVlieg and cutting metal. The tactile feedback you get from a manual machine is still valuable. You can feel how the tool is biting. You can hear the harmonics.
Plus, there's the "DeVlieg Retrofit" market. A lot of shops are taking these old frames—the "good iron"—and stripping off the old 1970s electronics. They'll add modern AC servo motors, a new CNC controller (like a Centroid or a Fanuc), and suddenly you have a machine with the structural integrity of a tank and the brains of a modern computer. It's often cheaper and better than buying a brand-new HBM from overseas.
What to Look for When Buying Used
If you're scouring auctions for a devlieg boring mill, you have to be a bit of a detective. These machines are heavy, so they aren't easy or cheap to move. You want to make sure the one you're buying isn't a "project" unless you really know what you're doing.
- The Ways: Check for scoring on the bed and column ways. If someone let the lubrication system go dry, the ways will show it. Scraping a DeVlieg back to factory specs is a dying art and incredibly expensive.
- Spindle Runout: Bring a dial indicator. Check the runout inside the taper. A beat-up spindle means your bores will never be round, and rebuilding a Spiramatic head isn't a job for a hobbyist.
- The Leadscrews: Check for backlash. While some backlash is expected on an older manual machine, excessive play can indicate a lot of hard miles.
- The Sound: Run the spindle through the entire speed range. It should hum, not growl. If it sounds like a coffee grinder, you've probably got bearing issues.
It's also worth noting that the "Diatrol" systems on older machines are often dead or temperamental. Most people just ignore them and install a modern 3-axis or 4-axis DRO. If the machine you're looking at has a working DRO already, that's a huge plus.
Maintenance Is the Key to Longevity
Owning a devlieg boring mill is a bit like owning a vintage luxury car. You can't just ignore it and expect it to perform. The lubrication system is the lifeblood of the machine. Most of them have an automatic oiling system that needs to be checked daily. If those lines get clogged with old, gummy oil, the ways will start to gall.
I always tell people: keep it clean. It sounds simple, but those big flat ways are magnets for chips. If chips get under the wipers, they'll act like sandpaper. A few minutes of cleanup at the end of every shift will add ten years to the life of the machine.
The Versatility Factor
It's easy to think of these as just boring machines, but they are surprisingly versatile. With a right-angle attachment, you can turn a DeVlieg into a horizontal machining center that can handle five sides of a part in one setup. You can do face milling, drilling, tapping, and even some light profiling.
The large table surface—the "platen"—is designed with precision T-slots that allow for very creative fixturing. Because the table is so stable, you can stack up some pretty tall parts without worrying about the machine flexing. That rigidity is why the devlieg boring mill became the gold standard for aerospace work back in the Apollo era. They were using these things to bore out components for the Saturn V rockets because nothing else could stay as true over a long distance.
Final Thoughts on the DeVlieg Legacy
There's something deeply satisfying about watching a well-maintained devlieg boring mill in action. It doesn't scream like a high-speed router; it just makes a purposeful, low-frequency sound as it peels off thick curls of steel.
Whether you're a shop owner looking for a reliable workhorse for repair jobs or a machinist who appreciates the "golden age" of American machine tools, the DeVlieg is a legend for a reason. It reminds us that while technology changes, the laws of physics don't. Mass, rigidity, and precision engineering never go out of style. If you find one that's been treated well, buy it. They literally don't make them like that anymore, and honestly, they probably never will again.