Milling, Shaping and Grinding Machines
Overview
Milling, Shaping and Grinding Machines are core material-removal processes studied in ITI Fitter Semester 4. Milling uses a rotating multi-tooth cutter to remove metal; shaping uses a single-point tool with reciprocating motion; grinding uses abrasive wheels for finishing and precision sizing. Understanding machine parts, cutting parameters, types of operations, and safety rules is essential for NCVT theory and practical papers.
Typed Notes
Milling Machine — Types, Parts and Operations
The column-and-knee type milling machine is standard in ITI workshops. Main parts: base, column, knee, saddle, table, overarm, arbor, and spindle. Horizontal milling uses arbor-mounted cutters (plain, side, form cutters); vertical milling uses end mills and face mills. Key operations: plain/slab milling, face milling, slot milling, gear cutting, and angular milling. Cutting speed formula: N = (1000 × V) / (π × D), where V is cutting speed (m/min) and D is cutter diameter (mm). Feed is expressed in mm/tooth, mm/rev, or mm/min.
Shaping Machine — Mechanism, Parts and Operations
The shaper uses a single-point HSS tool held in a tool post on a ram that reciprocates horizontally. The quick-return mechanism (Whitworth or crank-and-slotted-lever) makes the cutting stroke slower than the return stroke, saving time. Main parts: base, column, ram, tool head, clapper box, cross-rail, table, and vice. The clapper box lifts the tool on the return stroke to prevent drag. Operations include: flat surface shaping, angular cuts, keyway cutting, dovetail slots, and T-slots. Stroke length is adjusted by moving the crank pin radially on the bull gear.
Grinding Machine — Wheel Specification and Types
Grinding removes metal by abrasive action. Wheel marking example: A 46 K 5 V — A=Aluminium oxide abrasive, 46=medium grain size, K=medium grade (hardness), 5=medium structure, V=vitrified bond. Soft wheels suit hard workpieces; hard wheels suit soft workpieces. Surface grinder holds work on a magnetic chuck and reciprocates under the wheel. Cylindrical grinder rotates the workpiece between centres. Centreless grinder uses a regulating wheel to control workpiece speed and feed — no centres needed, ideal for bar stock. Wheel dressing with a diamond dresser restores sharpness and trueness.
Safety, Coolants and Defects
Safety rules: always use wheel guards; never grind on the side of a plain grinding wheel; wear goggles; check wheel for cracks by ring test before mounting; ensure blotter (paper washer) is used between flange and wheel. Common grinding defects: chatter marks (wheel too hard or unbalanced), glazing (wheel too hard, abrasive becomes smooth), loading (wheel too soft, chips clog pores). Coolant in milling: soluble oil (cutting oil + water) reduces heat and improves finish. In shaping, cutting oil is applied manually. Proper clamping of workpiece in milling vice prevents vibration and tool breakage.
Topics & Sub-topics
Har topic ke saath sub-topics aur example — chapter ka complete coverage.
01Milling Machine
- Types: horizontal, vertical, universal column-and-knee
- Main parts: knee, saddle, table, overarm, arbor, spindle
- Operations: slab milling, face milling, slot milling, gear cutting
- Up milling vs down milling (conventional vs climb)
Cutting a 12 mm wide keyway on a 40 mm diameter shaft using a 12 mm end mill on a vertical milling machine at spindle speed N = (1000 × 25) / (3.14 × 12) ≈ 663 RPM.
02Shaping Machine
- Quick-return mechanism: Whitworth crank-and-slotted-lever type
- Parts: ram, bull gear, clapper box, cross-rail, tool head
- Stroke length adjustment by radial crank pin position on bull gear
- Operations: flat surfaces, dovetail slots, T-slots, keyways
Machining a flat surface 150 mm long on a mild steel block — stroke length set to 165 mm (10% extra each side) by adjusting the crank pin outward on the bull gear.
03Grinding Machine
- Types: surface, cylindrical, centreless grinding
- Wheel specification five-symbol code: Abrasive-Grain-Grade-Structure-Bond
- Wheel dressing with diamond dresser to restore trueness
- Magnetic chuck used in surface grinding to hold workpiece
Wheel marked A 46 K 5 V used to grind a hardened steel shaft (60 HRC) on a cylindrical grinder; regulating wheel in centreless grinder set at 3° angle to give axial feed of ~2 mm/rev.
04Cutting Parameters and Formulae
- Spindle speed formula: N = (1000 × V) / (π × D)
- Feed: mm/tooth, mm/rev, mm/min
- Depth of cut: roughing 2–4 mm, finishing 0.1–0.5 mm
- Cutting speed for HSS cutter on MS: 20–30 m/min
Plain milling cutter dia 80 mm, cutting speed 25 m/min → N = (1000 × 25)/(3.14 × 80) ≈ 100 RPM; feed per tooth 0.05 mm, 10 teeth → table feed = 0.05 × 10 × 100 = 50 mm/min.
05Safety and Defects
- Ring test for grinding wheel crack detection before mounting
- Wheel defects: glazing, loading, chatter marks
- Blotter (paper washer) between flange and grinding wheel
- Coolant types: soluble oil for milling, cutting oil for shaping
A grinding wheel producing chatter marks on a surface grinder — diagnosed as wheel imbalance; wheel removed, balanced on a balancing stand, re-dressed with diamond dresser, chatter eliminated.
Key Concepts
Revision ke liye ek nazar — exam se pehle yahi padhna hai.
- 01Milling cutter rotates and workpiece feeds — up milling (conventional) feed opposes cutter rotation; down milling (climb) feed matches cutter rotation.
- 02Shaper stroke length is set by the position of the crank pin on the bull gear; cutting stroke is slower than return stroke due to quick-return mechanism.
- 03Grinding wheel is specified by: Abrasive – Grain size – Grade – Structure – Bond (e.g., A 46 K 5 V).
- 04Surface grinding, cylindrical grinding, and centreless grinding are the three main types of grinding used in ITI Fitter trade.
- 05Milling machine column-and-knee type is most common in workshops; spindle speed is changed by gear box or step-cone pulley.
Questions & Solutions
Pehle khud try karo — phir solution kholo. Yahi tariqa topper banata hai.
What is the quick-return mechanism in a shaping machine and why is it used?
Explain the five-symbol wheel marking system with an example: A 46 K 5 V.
Differentiate between up milling (conventional) and down milling (climb milling).
What is glazing in a grinding wheel? How is it corrected?
Calculate the spindle speed for a milling cutter of 60 mm diameter with a recommended cutting speed of 30 m/min.
Milling machines use rotating multi-tooth cutters for flat, angular, and profile surfaces. Shapers use a reciprocating single-point tool with a quick-return mechanism for flat and slotted surfaces. Grinding machines use abrasive wheels for precision finishing; wheel selection follows a five-symbol code. Safety practices — ring test, wheel guards, correct coolant — are critical for all three machines and frequently tested in NCVT papers.
Chapter-end quiz
4 MCQsOption tap karo — turant pata chalega sahi ya galat, explanation ke saath.
Q1.Which part of the shaping machine lifts the tool during the return stroke to prevent drag on the workpiece?
Q2.In the grinding wheel code 'A 46 K 5 V', what does the letter 'V' represent?
Q3.Which type of grinding machine does NOT require centres to hold the workpiece?
Q4.What is the recommended safety check before mounting a grinding wheel on the machine?
Mark karo — dashboard par progress dikhega.