Checking squareness with a try square; types and point angles of cold chisels and safe chipping.
Try square
A precision tool to check squareness (90°) and flatness of surfaces and to mark lines at 90° to an edge.
- Parts: stock and blade, fixed exactly at 90°. Made of hardened and ground steel.
- Size = length of the blade (e.g. 100, 150 mm).
- Checking: hold the stock firmly against the finished face, bring the blade down on the surface and look against light. No light gap = square.
Cold chisel
A hand cutting tool made of high-carbon steel, used with a hammer for chipping – removing metal, cutting sheets and cutting off rivet heads. "Cold" because it cuts metal in cold state.
Types
- Flat chisel – removing metal from flat surfaces, cutting sheets.
- Cross-cut chisel – cutting keyways and narrow grooves.
- Half-round chisel – cutting oil grooves, correcting drill hole position.
- Diamond point chisel – square corners and V-grooves.
- Web chisel – removing metal between chain-drilled holes.
Point angle of chisel
| Material | Point angle |
|---|---|
| Aluminium | 30° |
| Copper | 45° |
| Brass | 50° |
| Mild steel | 55° |
| Cast iron | 60° |
Harder the metal, larger the point angle. The chisel is held at about 35°–40° to the surface while chipping.
Mushroom head Grind off the mushroom head of a chisel – pieces can fly and hurt. Wear goggles and use a chipping screen.
Quick Revision
- Try square checks 90° and flatness (light gap test).
- Five types of chisels: flat, cross-cut, half-round, diamond point, web.
- MS 55°, CI 60°, brass 50°, Cu 45°, Al 30°.
Your progress is saved on this device.