Tools and surfaces used to mark out a job accurately before cutting.
Marking means drawing the lines, centres and outlines on the job from the drawing, so that the job can be cut and filed to size.
Marking media
| Medium | Used on |
|---|---|
| Chalk / whitewash | Rough castings and forgings |
| Copper sulphate solution | Filed or machined steel surfaces |
| Prussian blue | Finished surfaces; also for checking flatness in scraping |
| Cellulose lacquer (layout dye) | Finished surfaces – dries fast, lines are very clear |
Scriber and punches
- Scriber – hardened pointed steel tool for drawing lines.
- Prick punch (30°) – light marks for divider point location.
- Dot punch (60°) – makes witness marks along scribed lines.
- Centre punch (90°) – makes a large mark to start a drill.
Surface plate
A very flat, rigid plate (cast iron or granite) used as a datum surface for marking and checking. Grades 1, 2 and 3 (grade 1 is the most accurate). Never hammer on it; cover it when not in use.
Angle plate
Cast iron block with two faces machined exactly at 90°. The job is clamped to it to mark or machine surfaces square to each other.
V-block
A hardened steel block with a 90° V-groove. It holds round bars for marking centres and drilling. Used in pairs (matched set) with a clamp.
Quick Revision
- Prussian blue / layout dye on finished work, chalk on castings.
- Prick 30°, dot 60°, centre 90°.
- Surface plate = datum; angle plate = 90°; V-block = holding round jobs.
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