Engineering Processes — Marking, Cutting, Shaping & Drilling
From Raw Material to Finished Part
Engineering is the process of turning raw material into a finished product. Almost every product requires a sequence of operations: first the material is prepared, then marked out, then cut and shaped, then drilled or turned, and finally finished. Each stage removes material or changes its form. Choosing the correct process for each stage — and the correct tool for each process — is a core engineering skill.
The specification identifies material removal, shaping and manipulation, joining and assembly, and heat and chemical treatment as applications of engineering processes. This lesson covers marking out, cutting, filing, drilling, turning and milling. Joining and finishing are covered in the next lesson.
Marking Out
Marking out is the first operation on a new piece of material. Before any cutting takes place, the engineer transfers the dimensions from the drawing onto the material surface. This ensures that cuts are made in the right place and that the finished part will be within the required tolerance.
The key marking-out tools are:
- A scriber — a hardened steel pointed tool used to scratch fine lines onto metal. It works like a pencil on metal, leaving a thin precise line that can be seen when cutting.
- A centre punch — used to make a small indentation exactly where a hole is to be drilled. The indent stops the drill bit from wandering off the marked position when it first contacts the material.
- A try-square (engineers’ square) — used to check that lines are at right angles to a reference edge. Accurate right angles are essential for most engineering components.
- Vernier calipers and a steel rule — used to measure and transfer dimensions. A vernier caliper can measure internal and external dimensions to a high degree of precision.
The purpose of the centre punch is often misunderstood in exams. It does not mark a line — it creates a small indent that acts as a starting point for the drill bit. Without it, the drill bit will skate across the surface instead of cutting in the intended location.
Cutting
Cutting removes material by shearing it with a blade. The choice of cutting tool depends on the material type, the thickness of the material, and the complexity of the cut required.
A hacksaw is the standard hand tool for cutting metal, plastic and other hard materials. The blade is held in tension in a frame, which keeps it straight during the cut. Fine-tooth blades are used for thin sections and hard materials; coarser blades for thicker, softer stock. A hacksaw is slow but precise and requires no power supply.
A bandsaw is a power tool that uses a continuous loop of toothed blade running between two wheels. It can cut through thicker material much faster than a hacksaw and is especially useful for curved cuts. Bandsaws must be guarded correctly and the operator’s hands must never be in line with the blade.
Filing
Filing removes small amounts of material using a hardened steel file. It is used to smooth rough cut edges, bring a part to its final dimension, and remove burrs left by cutting. Files are classified by their cut (the pattern and spacing of the teeth) — a flat smooth file produces a finer surface finish than a flat bastard file, which removes material more quickly. Filing also removes the sharp burrs left on cut edges, which are a safety hazard and would cause injury if left on a finished product.
Drilling
Drilling creates circular holes in material using a rotating drill bit. In a school or college workshop, the most common machine used is the pillar drill (also called a bench drill or pedestal drill). The workpiece is clamped to the table and the drill bit is lowered into the material by a lever or quill feed. The pillar drill is safer than a hand drill for engineering work because the workpiece is clamped and the drill bit moves vertically in a controlled path — the operator’s hands are not near the rotating bit.
The drill speed must be set appropriately for the material being drilled. Softer materials generally require faster speeds; harder materials and larger drill bits require slower speeds to avoid overheating and breaking the drill bit. Engineers consult speed tables (often provided on data sheets) to select the correct speed.
Task: Drill a 6 mm hole in a piece of mild steel plate at a marked position.
Step 1 — Mark and punch: Use a scriber to mark the hole position from the engineering drawing. Use a centre punch and hammer to create a small indent at the marked point. This gives the drill bit a starting location and prevents it wandering.
Step 2 — Set up the machine: Select the correct drill speed for a 6 mm bit in mild steel (consult the speed table). Fit the 6 mm twist drill bit in the chuck and tighten the chuck key. Remove the chuck key before switching the machine on.
Step 3 — Clamp the workpiece: Clamp the steel plate firmly to the pillar drill table using a machine vice or clamps. Never hold the workpiece by hand — if the drill bit snags, the workpiece will spin and cause injury.
Step 4 — Drill the hole: Switch on the machine. Lower the drill bit slowly into the punched indent using the quill feed lever. Apply steady downward pressure. Use a cutting fluid or lubricant to reduce heat and prolong drill bit life when drilling metal. Do not force the drill bit.
Step 5 — De-burr: Switch off and wait for the spindle to stop fully before removing the workpiece. Use a de-burring tool or file to remove the sharp burr around the edge of the hole.
Turning on a Lathe
A centre lathe is used for turning — producing cylindrical, conical and threaded shapes from round bar stock. The workpiece is held in a rotating chuck; the cutting tool is mounted in a tool post and fed into the workpiece. A lathe can face off (produce a flat end), turn down a diameter, drill along the axis, cut threads, and produce tapers. The cutting tool must be set at the correct height and feed rate, and the lathe must not be operated without the appropriate guards in place.
A milling machine uses a rotating multi-tooth cutter to remove material from the top or sides of a workpiece. The workpiece is clamped to a table that moves in the X, Y and Z directions, allowing flat surfaces, slots and complex profiles to be produced. Slot milling cuts a channel into a surface; end milling removes material from the side of the workpiece. Unlike a lathe, where the workpiece rotates, on a milling machine the cutter rotates and the workpiece moves.
Shaping in its broadest engineering sense also includes forming processes such as bending sheet metal around a former or in a sheet metal bender. These processes do not remove material — they change the shape by plastic deformation. They are classified under shaping and manipulation rather than material removal.
On a lathe, the workpiece rotates and the cutting tool is fixed — used for cylindrical shapes. On a milling machine, the cutter rotates and the workpiece moves — used for flat surfaces, slots and profiles. Mixing these up is a common exam error.