What is trepanning?
Trepanning is a technique used for drilling larger hole diameters where machine power is limited as it is not as power consuming as conventional drilling where the entire hole is converted into chips. The trepanning tool does not machine the whole diameter, only a ring at the periphery. Instead of removing all the material in the form of chips, a core is left at the centre of the hole. Consequently, this method is for through-hole applications.
Set-up recommendations for trepanning
Rotating and non-rotating drills
The peripheral insert must be set 0.20 mm (0.008 inch) behind the inner cartridge.
- The drill should be positioned with the inserts on the horizontal axis
- The drill must not be offset from the workpiece centre line, with reference to the peripheral insert, by more than -0.15 mm (0.006 inch)
- The peripheral cutting edge (P) should be set to within +0.1 mm (0.004 inch) in the horizontal plane from the spindle centre line (CL)
Vertical set up
During the trepanning operation, when drill breaks through, the remaining core will fall down, which does not normally cause a problem.
Long and heavy cores may require a core support to prevent them from falling down and chipping the inner insert.
Rotating drill - core fixing
Drill a hole into the core. Fix plug in the hole to prevent the core (C) from falling.
Non-rotating drill - core support
If the drill is fitted with a core support, the drill should be mounted with the cartridges located on the vertical axis and the peripheral insert downwards.