Fitting Shop: Filing, Sawing and Drilling For students.

The fitting shop is where metal parts are shaped by hand using bench tools. Filing smooths surfaces flat, sawing cuts metal to length, and drilling makes round holes — the three basic hand skills every mechanical engineer learns first.

It matters because even in an age of CNC machines, fitting teaches you how metal behaves and how accurate your hands can be. Prototypes, repairs, dies and one-off parts are still finished on the bench, and a fitter who can work to 0.1 mm by hand understands machining at a gut level.

Key Concepts

• Bench vice: the heavy clamp bolted to the workbench that holds the workpiece firmly while you file, saw or drill.
• Files: hardened steel tools with cutting teeth — flat, half-round, round and triangular shapes; bastard (coarse), second-cut (medium) and smooth (fine) cuts.
• Hacksaw: a frame holding a replaceable toothed blade; teeth must point away from the handle so it cuts on the forward push stroke.
• Marking tools: the scriber scratches layout lines, the centre punch stops drills wandering, and the try square checks right angles.
• Twist drill: the standard drill bit, with two cutting lips meeting at a point angle of 118 degrees for general steel work.
• Cutting speed: drill edge speed in m/min. Feed: advance per revolution in mm/rev.

Formulas

• Cutting speed: v = (π × D × N) / 1000 metres per minute, where D is the drill diameter in mm and N is the spindle speed in revolutions per minute. Assumes the drill runs at constant rpm and the point angle suits the material.
• Hole depth by hand feed: keep feed light and steady; forcing the drill overheats the lips and snaps small bits.

Worked Example

A 10 mm hole must be drilled in mild steel at a cutting speed of 18.85 m/min. Find the spindle speed and check a practical setting.

1. Rearrange the formula: N = (v × 1000) / (π × D) = (18.85 × 1000) / (π × 10) = 18850 / 31.416 = 600 rpm.
2. Set the drilling machine to 600 rpm, clamp the plate flat, and centre-punch the hole location so the drill starts exactly on the mark.
3. Drill with light pressure and cutting oil, withdrawing the bit to clear chips, then deburr the hole edge with a file.
4. Check the hole with a 10 mm plug gauge or caliper — a clean hand-drilled hole should measure within about ±0.1 mm.

Common Misconceptions

• "Filing cuts on both strokes." A file cuts only on the forward push stroke — ease off on the return, or you dull the teeth.
• "Push harder to drill faster." Excess pressure overheats and breaks bits. Correct speed with steady light feed cuts faster and leaves a cleaner hole.
• "You can skip the centre punch." Without the punch dent, the drill tip skates across the steel and the hole lands off-centre — the most common beginner error.

Real-World Applications

• Prototypes: first versions of brackets, enclosures and fixtures are fitted by hand before tooling is ordered.
• Die and mould making: toolmakers still file and fit die components to micron-level feel.
• Maintenance: repair shops file, drill and tap replacement parts on the spot when machines break down.

The fitting shop shapes metal by hand: files cut on the push stroke, hacksaws cut forward with teeth pointing away, and drills need a centre-punch mark plus the right speed from v = πDN/1000.