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What happens when you flip the spindle in a vertical machining center? At IMTS, I saw a machine that answered this very question: ’s IM-8. I recently interviewed David Modig, the company’s president, to learn more about the challenges and opportunities posed by this unconventional machine construction.

Inverting Milling on Its Head

David Modig says that the IM-8, like most of the company’s machines, is best suited for aerospace parts that need to remove a lot of material. In particular, he positions the IM-8 as being particularly effective for large aerospace parts, cutting into difficult-to-machine metals where recutting chips would be an issue under normal circumstances — and semiconductor housings, which require some of the same difficult-to-meet machine requirements.

A 31-inch inverted trunnion enables users to load workpieces up to 28 inches in height and 47 inches in diameter, while the structure of the machine comes in much smaller than traditional mills that can handle parts of the same size. As Modig puts it, “With inverted milling you can almost hide the spindle more. You don’t need the extra stroke everywhere to reach the part.”

The IM-8 can perform milling, with four- and five-axis versions of the machine available, deep hole drilling up to a maximum depth of 20 inches and turning, the last of which Modig says particularly benefits from the orientation of the machine.

The machine can output 200 horsepower at its peak with a high-horsepower spindle for aluminum, with Modig saying that this is over twice of what comparable competing machines can reach. For harder metals that might require higher torque than horsepower, the company also offers a matching spindle.

Stability Starts From the Bottom

For both high-horsepower and high-torque operations, Modig suggests that the inverted position of the spindle will improve stability and rigidity. He refers to the tendency of spindles to show decreasing levels of stability the further away they move from their base and says that keeping X- and Y-axis movement closer to the ground minimizes the “flagpole” deflection effect. Additionally, the machines move the trunnion and the part closer to the spindle, relying on gravity to help with operational stability.

Modig says that the company’s machines show some of the best accuracy and rigidity on the market for five-axis trunnion machines, and particularly positions the IM-8 as a high-performance machine that emphasizes rigidity. “It’s just like a car,” he says. “When you hit the corner, do you have the right tires? The brakes? The chassis?” For hogging out hard materials, he argues that the IM-8 meets these requirements.

Keeping the Spindle Clear

David Modig says the IM-8 is not the company’s first attempt at a machine with an inverted spindle. In 1997, the company made a three-axis inverted machine under very different design principles. While this older machine solved issues with the recutting of chips and the related issues of tool load, Modig says one of its biggest issues was how chips could fall into the spindle, causing errors during tool changes. The tapers on the IM-8, however, largely mitigate this issue, preventing chips from entering and clogging the spindle.

Modig and his team are still studying how much the change in spindle orientation saves on coolant. While gravity can clear many chips from the work zone — especially in deep-hole drilling, turning still requires a high coolant flow. Modig also notes that aerospace structural parts will still require through-spindle coolant regardless of the spindle orientation.

Flipping Expectations

Despite the inverted spindle orientation, Modig says that workholding, parts loading and automation see few changes compared to traditional vertical machining centers. The trunnion table flips to an upright position during part loading, only returning to its inverted position during machining. This means shops can pair it with pallet systems and robots to load from the top or front of the machine — Modig notes that one of the few differences is that robots tend not to require long arms for front loading, as the trunnion is at what he says is a more convenient height.

To help keep the machines as compact as possible, the company has also created an automation division to perform turnkey integrations. Parts loading, washing and deburring are all standard automation offerings for the machines, but Modig says that users can still customize the automation systems to meet their particular needs, no matter if they are automating the IM-8 or one of its other, more conventionally oriented machines.