Aircraft Extension Drills

What it is

An aircraft extension drill has a jobber-type cutting end on a long straight body. It is sold by diameter and overall length, for example 6 in or 12 in. The extra length lets a mechanic reach past stringers, frames and other structure to drill a hole that a standard drill cannot get to. They are common in aircraft, truck body and HVAC work. ANSI B94.11M covers extension drills, and NAS 907 covers aircraft twist drill types used in aerospace.

How to identify

The flutes take up only a short part of the length. The rest is a plain round body the same diameter as or slightly smaller than the drill. The label gives both the drill size and the overall length. Many aircraft drills have a 135° split point and are made of HSS or cobalt.

How it differs from other long drills

Key points

• Order by diameter and overall length. Both are needed for a correct replacement.
• Because the flutes are short, an aircraft extension drill is not for deep holes. Chips cannot clear once the flutes are buried.
• The long body whips at high speed. Run slower than a jobber of the same diameter and support the drill near the work with a guide or drill bushing where possible.
• Number and fractional sizes used for rivets and fasteners are the most common in aerospace work. Check the drill size chart for decimal equivalents.
• NAS 907 type and point details matter on aerospace jobs. Follow the customer's specification.

Common mistakes

• Replacing a 12 in extension drill with a 6 in one because the diameter matched.
• Using an extension drill to drill a deep hole and packing the short flutes.
• Running a long extension drill at full jobber speed and bending it.
• Confusing aircraft extension drills with taper length drills, which have long flutes.

Governing standards: ANSI B94.11M (twist drills); NAS 907 (aircraft twist drills). Manufacturer catalogs for exact dimensions.

Reference only. Verify against the current governing code or standard, the manufacturer's data and the project documents before use. Apps for Distributors disclaims liability arising from reliance on this reference.