Turning Workholding Fixture Enables Stable Machining at 1,200 RPM
When Skilled Manufacturing, Inc. (SMI) needed its first mill-turn workholding application, All World Machinery Supply engineered an ARROW® Workholding Fixture to securely locate and hold an asymmetric hydraulic housing at table rotation speeds up to 1,200 RPM across multiple operations in a single setup. The system delivers a repeatable 40-minute cycle time, consistent surface finish, and eliminates vibration-driven variation.
“I call it an engineering masterpiece,” said SMI Project Management Lead Jason Dreffs.
Seeking Perfect Stability
Based in Traverse City, Michigan, SMI is a global leader in precision machining, production, assembly, and testing across the automotive, aerospace, medical, and defense sectors. It partners with All World for custom fixturing.
“We’ve had a long track record with them. They’re our go-to for hydraulic clamping workholding fixtures. They understand our processes, our equipment, and the parts we run, so it’s always an easy fit,” said Dreffs.
In fall 2025, Skilled Manufacturing, Inc. needed to produce an aerospace hydraulic housing that required final machining under tight tolerances and demanding surface finishes. The process called for an Okuma MU-4000V-L with full five-axis milling and 1,200 RPM lathe turning to enable full feature access.
The fixture had to maintain precise location and consistent clamping force under bidirectional loads, where a minor imbalance at speed could impact surface finish and dimensional accuracy. Complicating the setup, the part was already at the final stage of machining, so scrapping at this point would result in an expensive loss.
“One of the challenges was the proportion of the part relative to the machine table,” said All World Design Engineer Manuel Vega. “We had very little room to accommodate link clamps and work supports.”
Foundation is Key
Engineers began by evaluating the Okuma MU-4000V-L and aligning the fixture design with machine-specific parameters, including hydraulic pressure capacity, porting layout, and the table interface. This analysis led to the development of Platform 152, a dedicated interface enabling quick fixture changeover while connecting two hydraulic and two pneumatic circuits and ensuring repeatable positioning in the machine.
Platform 152 routes double-acting clamp and unclamp circuits through a unified manifold, with integrated air sensing and blowoff for in-cycle verification and chip evacuation. Hydraulic couplers and precision locators provide repeatable connection points for rapid fixture exchange without removing the base system, reducing changeover time and variability while maintaining alignment.
Multiple actuators required varying operating pressures to control clamping forces. This was achieved by utilizing control valves downstream from the platform on the fixture. This flexibility allows SMI to adjust holding force as needed.To support the high RPM operation, Platform 152 incorporates additional safety features, including pilot-operated check valves and mechanically locked clamping elements. These components hold position even in the event of hydraulic pressure loss, ensuring the system does not rely solely on the source hydraulic pressure during rotation.
Unique Locating and Multi-Stage Clamping
Engineers used the collet as a primary locating element rather than a clamping device, paired with a diamond pin to establish position and hold a 0.0002" internal diameter tolerance prior to clamp engagement. The collet provides .012" of load clearance, and locates the part within .0002" when expanded, without clamping the locating bore. This arrangement also protects the primary locating bore from "witness marks" by introducing no force to the bore itself.Fine-tuning part position in X and Y is achieved through layered, key-guided plates, enabling fine alignment within a constrained envelope without disturbing the base interface.
Once located, the part is supported with work supports positioned to resist cutting forces and centrifugal loading at 1,200 RPM. The combination of support, clamping, locating, and balancing is critical to maintaining positional accuracy and surface integrity.
Hydraulic clamping is routed internally through the fixture body and actuated from below, preserving full access to part features and eliminating obstructions within the cutting envelope. Four link clamps with independent flow control engage angled surfaces to deliver consistent force under load.
All functions operate through a common clamp circuit, requiring controlled sequencing and pressure management to maintain location, without leaving any marks on the part.
The multiple circuits and actuation sequences increased baseplate complexity, particularly in port routing, while maintaining reliability and service access. Prior to release, a 3D-printed nest was used to validate fit, access, and potential interferences beyond CAD, reducing risk ahead of production.
Controlled at Speed
To ensure smooth rotation at 1,200 RPM, the entire system was balanced using two-plane dynamic balancing to meet ISO 21940 requirements for vibration and spindle load, ensuring stable operation for the lathe operations.
This required developing custom balancing tooling, including a 5-inch diameter, 48-inch-long shaft with a mounting flange designed to interface with the fixture and platform. The tooling was designed with reuse in mind, supporting future mill-turn fixture programs.
“One of the toughest parts was anticipating what needed to be built in so it works not just for this project, but for the next ones as well,” Vega said.
Production Results
When the system arrived at SMI in March, Dreffs noted that the CNC operator ramped it up to 1,100 RPM and could hardly believe how smoothly it ran.
The fixture has already proven itself in early production, with initial parts successfully running through the full process during setup. Upfront engineering around clearances, balance, and clamping ensured smooth production. All World is already working on three additional mill-turn workholding fixtures for other SMI projects.
“We put a lot of confidence in All World,” Dreffs said. “They know our CNC programmers, ask the right questions, and deliver solutions that just work. It’s a no-brainer. Workholding like this is where it all starts. It puts us in a completely different spot in the market.”
