Vertical Boring Mill

Overview

A vertical boring mill, often called a vertical turret lathe, turns large and heavy parts that would be awkward or unsafe to swing on a horizontal lathe. The part sits flat on a rotating horizontal table and is gripped by power jaws on the table centre line. Tools mounted on a fixed structure above and beside the part feed into the rotating work to bore holes, face flat surfaces and turn outer diameters. Putting the spin axis vertical means gravity helps hold the part down and centred, so the machine handles flywheels, gear blanks, valve bodies, turbine casings and bearing rings up to two metres across.

The machine is built around the Base & Rotary Table, whose rotary table floats on a Hydrostatic Table Bearing so that several tonnes of part turn with low friction and high stiffness. The Column Structure rises from the base and carries the Cross Rail, a horizontal beam that can be raised to suit the part height. Riding the cross rail is the Vertical Ram Head, the main tool slide, and a separate Side Turret Head hangs off the column to work the outside of the part at the same time.

Table and drive

The heart of the machine is the table. The Rotary Table is a heavy faceplate, and the Self-Centring Jaws clamp the part to its centre. Because the table carries the full weight of the work and the radial cutting load, it runs on the hydrostatic bearing rather than rolling elements: pressurised oil from the Hydraulic System forms a film that the table glides on, which gives near-zero friction at start-up and damps chatter. The Table Drive turns the table through a two-step reduction so the Table Spindle Motor can deliver high torque at low speed for big-diameter cuts. As a tool feeds outward, the control raises the table speed to hold a constant surface speed at the cutting edge, which keeps the finish even from rim to centre.

Tool heads

The Vertical Ram Head does most of the cutting. Its Vertical Ram is a stiff square box that extends down from the Ram Saddle on the cross rail, and on its end an indexing Indexing Tool Turret carries up to five tools. The Ram Feed Servo feeds the ram down into the part to bore or face, while the saddle traverses the cross rail to set the cutting radius. The Side Turret Head adds a second cutting station: its Side Cross Slide rides the column ways and feeds tools radially to turn the outer diameter. Running both heads together cuts the inside and the outside of a ring in one chucking, which keeps the two surfaces concentric and roughly halves the cycle time.

Structure and rigidity

Heavy turning generates large, often interrupted cutting forces, so the frame is massive. The Base Casting and Column Casting are ribbed grey-iron castings chosen for their damping, and the larger mills close the frame into a bridge with a second column for extra stiffness. Every sliding joint runs on hardened, ground guideways: the Column Way guides the cross rail vertically and the Linear Guide Rail elements carry the saddle and the slides. Feed motion comes from preloaded Ball Screw drives backed by Position Encoder feedback, so the control knows true slide position rather than commanded position.

Hydraulics and coolant

The Hydraulic System does more than feed the table bearing. The same Hydraulic Pump clamps the power jaws, counterbalances the weight of the ram so the feed servo only has to control motion, and operates the cross-rail clamps. Pressure at each circuit is watched by a Pressure Sensor so the control can confirm the part is gripped before the table turns. The Coolant System floods the cut to clear heat and chips; because big steel cuts make heavy swarf, a Chip Conveyor drags the chips out of the coolant pan into a bin instead of relying on the coolant flow alone.

Control and use

The CNC Control runs the table and both heads as coordinated axes, often as two independent channels so each tool head can run its own cycle. The operator programs the part at the Operator Display, entering diameters, depths, feeds and the tool list; the control then sequences roughing and finishing passes and manages the turret indexing. Typical work is large bearing rings, gear and pulley blanks, brake rotors for rail and mining stock, pump and valve bodies, and wind-turbine and machine-tool castings. Variants range from single-column open-side machines for medium parts to double-column bridge machines and twin-table mills that load one part while the other is cut.