Trepanning

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 center of the hole. Consequently, this method is for through-hole applications.

Set-up recommendations for trepanning

Adjusting screw

Rotating and non-rotating drills

The peripheral insert must be set 0.20 mm (0.008 inch) behind the inner cartridge.

Non-rotating drill

• The drill should be positioned with the inserts on the horizontal axis
• The drill must not be offset from the workpiece center 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) from the spindle center line (CL) on the horizontal plane

Core handling

Vertical set-up

During the trepanning operation, when the drill breaks through, the remaining core falls down, which does not normally cause problems.

Horizontal set-up

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 the 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.