Milling Machine Operations

• Milling is machining a surface using a toothed cutter to produce plain or formed surfaces.
• Knee-and-column type milling machines are versatile and commonly used in workshops.
• These machines have a spindle fixed in the column and a table that moves in longitudinal, transverse and vertical directions.
• Knee-and-column machines include plain horizontal, universal, and vertical models.
• Plain horizontal machines have a horizontally located spindle.
• Universal machines are similar to plain horizontal ones but include a swiveling table for cutting helical grooves.
• Vertical machines have a vertically located spindle.
• Machine capacity is determined by the size of the table's working surfaces, the length of travel, and the maximum spindle-to-table/column distance.

Milling Machine Elements

• The column and base form the machine's foundation, made of cast iron for rigidity and vibration control.
• The base also acts as a cutting fluid reservoir with a circulation pump.
• The column houses the spindle in precision bearings, driven by a vee-belt and gearbox, allowing speed selection.
• The column has guideways for vertical knee movement.
• The knee provides vertical table movement via column guideways.
• Power feed is available with a gearbox, offering 12 feed rates.
• A leadscrew raises and lowers the knee via a handwheel.
• The knee has guideways for saddle support and transverse movement.
• A lock secures the knee in any vertical position on the column.
• The saddle sits on the knee guideways, enabling transverse table movement.
• Power feed is available through a gearbox with various feed rates.
• A leadscrew and handwheel offer alternative hand movement.
• Clamps secure the saddle to the knee.
• The saddle has dovetail guideways for longitudinal table movement.
• The table provides a surface for workpieces and equipment, with tee slots for clamping.
• Dovetail guides locate in the saddle's guideways for straight-line longitudinal movement.
• Power feed is provided from the knee gearbox through a leadscrew.
• Alternative hand feed is available via handwheels, with stops for automatic feed disengagement.
• The spindle, mounted in precision bearings, drives the milling cutters.
• Cutters mount directly or via holding devices, secured by a drawbolt.
• Milling spindles have a standard tapered nose for interchanging cutters/devices.
• The taper angle is 16° 36', with diameters of 30, 40, or 50 IST.
• Tapers use driving keys to transmit drive.
• Cutters are located on a centering arbor, with tapped holes and driving keys.
• Horizontal machine spindles are fixed axially.
• Vertical spindles allow axial movement via a handwheel.
• Vertical spindles run in a quill, moved by a rack and pinion, and locked in place.
• Most horizontal machine cutters are held on an arbor, supported at the outer end to prevent deflection.
• The arbor support bracket is clamped to an adjustable overarm.
• The overarm can be moved in/out or fully retracted.
• Two bolts lock the overarm, and the arbor support is locked within the dovetail.
• The solid bearing facilitates arbor rotation during spindle use.
• Machine guards enclose the working area, protecting from swarf and coolant.
• Guards slide/swing for access and use polycarbonate panels for visibility.
• Electrical safety interlocks prevent operation with an open guard.

Machine Controls

• The controls of horizontal and vertical milling machines are identical.
• Spindle speeds are selected via levers, with the speed indicated on the change dial.
• An 'inching' button allows gear alignment during speed changes.
• A switch controls the cutting-fluid pump and spindle rotation direction.
• Feed rates are selected by a lever, indicated on the feed-rate dial.
• Lever controls longitudinal table feed direction.
• Adjustable trip dogs disengage feed movement, and limit stops prevent damage.
• Lever controls cross/vertical traverse, with movement of another lever engaging feed in the required direction.
• Rapid traverse is engaged by pulling a lever upward, which disengages upon release.
• A single crank handle provides alternative hand feed, with spring ejectors for safety.

Milling Cutters

• Milling cutters can be classified by mounting method.
• Arbor-mounted cutters have a central hole for mounting on an arbor
• Screwed-shank cutters are held in a special chuck.
• Large facing cutters mount directly on the spindle nose.

Arbor-Mounted Cutters

• Cylindrical cutters have teeth on the periphery only, used for producing flat surfaces.
• Helical teeth reduce shock.
• They come in various sizes.
• Side-and-face cutters have teeth on the periphery/face and both sides, used for steps and slots.
• Straddle milling involves using these cutters in pairs.
• Teeth are straight or helical.
• Staggered-tooth side-and-face cutters are designed for deep-slotting, with alternating helix teeth and removed side teeth.
• Angle-milling cutters can be single or double angle, used on angle faces or for chamfering.
• Single-angle cutters have angles of 60° to 85°, and double-angle cutters have angles of 45°, 60°, and 90°.
• Single corner-rounding cutters have a concave quarter circle, used to produce a corner radius.
• Shell end-milling cutters have teeth on the circumference and one end.

Screwed-Shank Types

• End-milling cutters have helical teeth on the circumference and teeth on one end, used for milling slots, profiling, and facing narrow surfaces.
• Non-center-cutting cutters cannot be fed along their axis.
• Center-cutting types can be fed along their own axis allowing drilling and plunging
• Slot drills have two/three helical teeth and can be fed along their axis for keyways and blind slots.
• Tee-slot cutters are designed for milling tee slots, with alternating helix teeth and removed side teeth, to produce a tee slot.
• Dovetail cutters have teeth on the angle face and end face, used for dovetail slides, with 45° and 60° angles.
• Corner-rounding cutters produce a radius along the workpiece edge, with radii up to 12 mm.

Direct-Mounted Types

• Face-milling cutters, or "face mills", are used to face large surfaces, consisting of a steel body with clamped inserts

Cutter Mounting:

• Arbor-mounted cutters have a hole through the center and are mounted on an arbor.
• The arbor is held and driven via the drawbolt and flange.
• Cutters are positioned using spacing collars and secured with an arbor nut.
• A running bush supports the arbor.
• Stub arbors mount cutters close to the spindle. They are located, held, and driven similarly to a standard arbor
• Screwed-shank cutters are mounted in a special chuck using a collet and locking sleeve.
• Large face mills are mounted directly on the spindle nose, located by a centering arbor and driven by spindle keys

Work Holding

• Workpieces can be clamped directly, using tee slots, avoiding damage.
• Vises are versatile for holding workpieces, requiring accurate alignment with machine movements.
• A rotary table is suited to machining circular surfaces.
• The workpiece is rotated to produce a circular profile with dial at the periphery that is graduated in degrees.
• The rotary table can be used for holes in a pitch circle diameter (pcd).
• A dividing head is for slots, grooves, or teeth spaced around the circumference of a cylinder or disk.
• In a vertical position is can drill holes on a pcd similarly to a rotary table.
• The dividing head has a spindle with a worm wheel and a single-start worm, using an index plate with different-spaced holes.

Milling Machine Operation

• The switch panel contains a "B" button to start the feed motor facilitating setting up when feed movements are required without spindle rotation.
• The "G" button starts the spindle and feed motors.
• The "R" button stops the machine.