From DT Online
Dot Punches are similar to Centre Punches but have a sharper point ground to an angle of 60 degrees by holding it Tangentially to a Tool Grinder and rotating it (i.e. in a similar manner to a Scriber). This tends to create grinding marks which run along the point and strengthen it rather than weakening it by going across.
Features and Uses
Dot Punches are held at an angle to the intersection or line to be marked and either lightly struck once with a hammer or, alternatively, Automatic Dot Punches are available, as shown, which are simply pushed down to activate.
If Dot Punches are used to mark where a large hole crosses each of its centre lines, for instance, accurate work would result in each ‘dot’ being halved across its diameter.
- In general, Dot Punches have a sharper point (i.e. 60° instead of 90°) and need only the lower ranges of impact force (e.g. 20N to 50N).
- Automatic punches are simply pushed down against the work-piece and do not need to be struck - indeed, should NOT be struck with a hammer.