Files, Hacksaws and Chisels
Overview
Files, Hacksaws and Chisels are the three fundamental hand-cutting tools used in a Fitter's workshop. Files remove metal by abrasion, hacksaws cut metal by tooth action, and chisels cut or chip metal by striking force. Understanding their types, grades, parts, and correct usage is essential for NCVT ITI Fitter Semester 1 examination. These tools are used daily in fitting, maintenance, and fabrication work across all engineering industries.
Typed Notes
Files — Parts, Types and Grades
A file consists of: Tip (point), Body (face and edge), Heel (shoulder), Tang, and Handle. Files are classified by shape: flat, hand, square, round (rat-tail), half-round, triangular (three-square), knife, and needle files. By cut: single cut (one row of teeth), double cut (two crossing rows), rasp cut (individual raised teeth for wood/soft material), and curved cut. By grade (coarseness): Rough → Bastard → Second Cut → Smooth → Dead Smooth. Bastard files are most commonly used for general metal removal in a fitter's shop.
Hacksaw — Blade Selection and Frame
A hacksaw frame holds a 300 mm (12-inch) blade under tension using a wing nut. Frames are fixed or adjustable (for 250 mm and 300 mm blades). Blade material is High Speed Steel (HSS) or bi-metal (HSS teeth on flexible alloy steel back). TPI selection rule: at least 2–3 teeth must be in contact with the workpiece at all times. Use 14 TPI for soft metals (aluminium, brass), 18 TPI for mild steel, 24 TPI for thin sections/pipes, 32 TPI for thin sheets and tubing. Cutting stroke is the forward stroke; pressure is released on the return stroke.
Chisels — Types, Angles and Use
Chisels used in fitting are: Flat (cold) chisel — most common, for chipping flat surfaces; Cross-cut (cape) chisel — for cutting narrow grooves and keyways; Half-round chisel — for oil grooves in bearings; Diamond-point chisel — for V-grooves and corners; Web (round-nose) chisel — for curved grooves. All are made of High Carbon Steel (HCS), hardened and tempered. Cutting angles: Brass/bronze 45°, Mild steel 60°, Cast iron 60–65°, Hard steel 70°. The chisel is struck with a ball-peen hammer (0.5 kg to 1 kg). Mushroomed chisel heads must be reground immediately to prevent injury.
Safe Use and Care of Cutting Tools
File care: Never use a file without a handle (tang can pierce the palm). Never use a file as a lever or hammer. Clean files with a file card (wire brush) to remove pinning (metal clogging). Apply chalk on file face to reduce pinning on soft metals. Hacksaw care: Do not twist the blade; use full-length strokes (about 40–50 strokes per minute). Replace blade when teeth are stripped. Chisel safety: Always use a properly sized hammer; hold chisel with a chisel holder or tongs when starting a cut. Wear safety goggles to protect from flying chips. Grind mushroomed heads before use.
Topics & Sub-topics
Har topic ke saath sub-topics aur example — chapter ka complete coverage.
01Files
- Parts of a file: tip, body, heel, tang, handle
- Classification by shape: flat, round, half-round, triangular, square
- Classification by cut and grade: single/double/rasp cut; rough to dead smooth
- Pinning and file card cleaning
A 250 mm flat bastard file is used to remove excess metal from a mild steel workpiece after rough machining — bastard grade removes material fast while still leaving a reasonably smooth surface.
02Hacksaw Blades and Frame
- Frame types: fixed and adjustable (250 mm and 300 mm)
- Blade materials: HSS and bi-metal
- TPI selection: 14 TPI for aluminium, 18 TPI for MS, 24 TPI for pipes, 32 TPI for thin sheets
- Tooth set types: alternate set, wave set, raker set
Cutting a 25 mm diameter mild steel rod requires an 18 TPI bi-metal blade at 40–50 forward strokes per minute with pressure applied only on the forward stroke.
03Chisels — Types and Cutting Angles
- Types: flat, cross-cut (cape), half-round, diamond-point, web (round-nose)
- Material: High Carbon Steel, hardened and tempered
- Cutting angles by material: brass 45°, MS 60°, hard steel 70°
- Striking tool: ball-peen hammer 0.5–1 kg
A cross-cut (cape) chisel ground to 60° is used to cut a 6 mm wide keyway groove in a mild steel shaft before fitting a key.
04Safe Handling and Maintenance
- File safety: always fit handle before use; never use as lever
- Hacksaw safety: full-length strokes, no twisting, 40–50 strokes/min
- Chisel safety: regrind mushroomed heads; wear safety goggles
- Storage: hang files separately to prevent teeth damage
A fitter notices the head of a cold chisel has mushroomed after heavy use; he immediately grinds it on a bench grinder before continuing work to prevent metal splinters from flying into his eyes.
05Selection Criteria for Cutting Tools
- File selection: material hardness, surface finish required, and stock removal amount
- Hacksaw blade selection: TPI based on workpiece thickness and material
- Chisel angle selection: softer material = smaller included angle
- Length and grade of file vs. job size
To finish a 100 mm × 50 mm mild steel flat surface to Ra 1.6 µm smoothness, a fitter first uses a 300 mm bastard file for bulk removal, then switches to a 300 mm smooth file for the final finish pass.
Key Concepts
Revision ke liye ek nazar — exam se pehle yahi padhna hai.
- 01A file is graded by cut (single, double, rasp, curved) and grade (rough, bastard, second cut, smooth, dead smooth) — 5 grades total.
- 02Standard hacksaw blade length is 300 mm (12 inches); blade pitch is selected as 14, 18, 24, or 32 TPI based on material thickness.
- 03A cold chisel is made of high-carbon steel and the cutting angle (included angle) for mild steel is 60°.
- 04Files are measured from the tip to the heel (excluding the tang); common lengths are 100 mm to 450 mm.
- 05The set of hacksaw blade teeth (alternate set, wave set, raker set) prevents blade jamming in the cut (kerf).
Questions & Solutions
Pehle khud try karo — phir solution kholo. Yahi tariqa topper banata hai.
What is the standard length of a hacksaw blade used in a fitter's workshop, and what material is a bi-metal blade made of?
Name the five grades of files in order from coarsest to finest.
What is the correct cutting angle (included angle) of a flat cold chisel for cutting mild steel, and why does it differ for brass?
Explain the rule for selecting the correct TPI of a hacksaw blade with an example.
What is 'pinning' in a file, and how is it prevented or removed?
Files (graded by shape, cut, and coarseness), hacksaws (300 mm HSS/bi-metal blades selected by TPI), and chisels (HCS tools with specific cutting angles per material) are the core hand-cutting tools of Semester 1. Correct selection, safe handling, and regular maintenance of these tools ensure accurate fitting work and prevent workshop accidents.
Chapter-end quiz
4 MCQsOption tap karo — turant pata chalega sahi ya galat, explanation ke saath.
Q1.Which type of chisel is used for cutting oil grooves in a bearing?
Q2.What is the TPI of a hacksaw blade recommended for cutting thin-walled steel tubes?
Q3.A file is measured for its length from which point to which point?
Q4.Which material is used to manufacture a cold chisel?
Mark karo — dashboard par progress dikhega.