Description
Handheld core drilling starts badly more often than it ends badly. Before the crown has cut a kerf deep enough to hold itself, the barrel skates across the surface, and by the time it bites you are half an inch off the mark with a scarred slab to explain.
What the pilot bit does
The centering guide mounts through the middle of the barrel and puts a small drill point exactly on your mark. That point takes the load for the first few seconds and holds the barrel concentric while the crown establishes its own kerf. Once the kerf is deep enough to guide the barrel on its own — usually a quarter inch or so — the pilot comes out and the hole carries on as normal.
When you need one and when you do not
You need it for handheld drilling, on any vertical surface, and on anything where the finished face will be visible. You do not need it on a stand-mounted rig: the stand and its anchor already fix the position, and a pilot adds nothing.
Remove the pilot as soon as the kerf is established. Leaving it in the hole is how they get bent, and a bent pilot pushes the barrel off center — the precise fault it was bought to prevent. Related: core bit accessories and the core bit size and thread guide.
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