ZIMSEC O Level · Metal Technology and Design · Form 1, Form 2, Form 3
Sawing
The hacksaw blade's teeth point forward (cuts on the push stroke). Use fine teeth (32 per 25 mm) for thin sheet and tube, coarser (18 per 25 mm) for thick bar. At least three teeth should touch the work. Tin snips cut thin sheet metal.
Filing
- Types: flat, hand, half-round, round, square, triangular and needle files.
- Cuts: rough, bastard, second cut, smooth.
- Cross filing removes metal quickly; draw filing gives a smooth finish. Clean files with a file card.
Drilling
Use a pillar drill or hand drill with twist drills. Centre punch first; clamp work in a machine vice; use slower speeds for larger drills and harder metals; use cutting fluid on steel.
Threading
- Internal threads: drill the tapping size hole, then use taper, second and plug taps in a tap wrench.
- External threads: use a die in a die stock.
- Turn half a turn forward and a quarter turn back to break the chips; use lubricant.
The centre lathe
Used for facing, turning, drilling, boring, knurling and cutting threads on round work.
Exam tip: Hacksaw teeth must point forward – fitting the blade backwards is a classic exam mistake.
Check yourself
- Which way should hacksaw teeth point?
- Name the tools used to cut an internal thread.
- Why is a file card used?
Show answers
- Forward, away from the handle.
- Taps (taper, second and plug) in a tap wrench.
- To clean metal particles (pinning) from the file teeth.
Questions about this topic (0)
No questions about this topic yet.
Sign in or create a free account to join in.