Horizontal Boring Mill Product

Overview

A horizontal boring mill machines large, heavy workpieces — gearbox casings, turbine housings, press frames, diesel-engine blocks — that would be impractical to swing on a lathe or mount on a vertical machining centre. Its defining feature is a horizontal Boring Spindle running inside an extendable W-Axis Quill, so the tool can reach deep into a stationary workpiece rather than the workpiece rotating around the tool. The part sits on a Rotary Table Assembly that indexes or contours about the vertical B axis, letting one setup expose all four sides to the spindle.

The table-type configuration described here moves the column in X along the Bed and Saddle Assembly, the headstock in Y up the Column Assembly, and the quill in W along the spindle axis, while the table provides rotation. Floor-type variants fix the workpiece on floor plates and add a Z-travelling column for parts beyond 20 t.

How it works

Cutting happens at the spindle nose. The boring spindle, hardened and ground to run within 0.005 mm TIR, is driven through a two-range Spindle Gearbox: the low range multiplies motor torque for 400 mm-class boring at 20–60 rpm, the high range reaches 3,000 rpm for drilling and face milling. A hydraulic Drawbar pulls the toolholder retention knob into the ISO 50 taper with 25–40 kN of spring force and releases it with a hydraulic cylinder during tool change.

The quill is what separates a boring mill from a milling machine. It slides the rotating spindle up to 700 mm out of the Headstock Assembly under NC control, so a line bore through a long casing can be cut from one side without repositioning. Because an extended quill loses stiffness roughly with the cube of overhang, controls compensate sag electronically and operators keep extension short for finishing passes.

Axis motion follows machine-tool convention: each axis pairs a Ball Screw with a Servo Motor and closes the position loop on a linear Encoder scale rather than the motor shaft, which removes screw pitch error and thermal growth from the measurement. The headstock's mass — several tonnes — is balanced by a chain-hung Counterweight inside the column so the Y screw only accelerates mass instead of holding it against gravity.

The rotary table carries the workpiece on a T-slotted Table Platen riding a crossed-roller Table Bearing. A duplex worm Helical Gear Pair with anti-backlash preload drives rotation; for heavy cuts a hydraulic Table Clamp locks the platen so cutting forces pass into the bed rather than the worm flanks. Indexing to 0.001° lets bores machined from opposite faces meet in the middle of a casing within hundredths of a millimetre.

Structure and accuracy

Everything rests on seasoned grey-iron castings. The Bed Casting and Column Casting are ribbed box sections, stress-relieved before final grinding of the Vertical Ways and bed ways. Installation matters as much as the iron: the bed is set on a dozen Leveling Pads over a reinforced foundation and levelled to about 0.02 mm/m, then re-checked after the foundation settles. Telescopic Way Covers keep chips and coolant off the sliding surfaces, and the Lubrication System system injects metered way oil through Metering Valves on a timed cycle, monitored by a Pressure Sensor that alarms on a blocked line.

Tooling

The Tooling System package extends the machine beyond what the quill alone can cut. A U-axis Facing Head mounts on the spindle nose and moves a tool radially under NC control while rotating, turning external diameters, facing flanges and cutting tapers — operations otherwise reserved for a lathe. Boring Bar Set supported in line-boring bushings handle long bearing tunnels. Day-to-day drills, face mills and boring heads live in the Tool Magazine and are swapped by the twin-gripper ATC Arm in under ten seconds.

Control and support systems

The CNC Control System cabinet houses the CNC Unit and one Servo Amplifiers channel per axis plus spindle. Volumetric compensation tables correct geometric errors measured at commissioning with a laser interferometer, and thermal sensors in the column and headstock feed growth-compensation models, since a 4 m column expands roughly 45 µm per °C. The operator works from a swing-arm Operator Panel with handwheel and overrides.

Chip and heat management is sized for roughing cuts that remove hundreds of cm³ of steel per minute: dual Coolant Pump units feed flood nozzles and 20–70 bar through-spindle coolant from the Coolant Tank, while a hinged-belt Chip Conveyor carries swarf out of the bed trough continuously. Typical machines achieve positioning accuracy of 0.008–0.015 mm over full travel and bore roundness under 0.005 mm, which is why boring mills remain the standard tool for large housings a half-century after their geometry was settled.