Cutting Tools Reference Library · Technical Reference

Indexable Insert Drills & Spade Drills

Indexable insert drills and spade drills use a replaceable cutting tip on a steel body to make larger holes at lower cost per hole. This sheet compares the two, explains their limits and lists what the machine must provide.

Ref CT-0015

Draft, open for review. Check every value against the governing standard and the manufacturer’s data before use.

What it is

An indexable insert drill has a steel body with two pockets near the tip. One insert cuts the center of the hole and the other cuts the outside. When an edge wears, the insert is rotated (indexed) or replaced and the body is kept. These drills are usually short, in the range of about 2 to 5 times the diameter, and make a flat-bottom hole.

A spade drill has a holder with a slot at the tip that takes a flat blade (the spade). The blade sets the hole diameter, so one holder covers a range of sizes. Spade drills are made in longer lengths than insert drills and are used for large holes and deeper holes on machines, lathes and boring mills. Blades are high-speed steel, cobalt or carbide.

How to identify

Insert drills show two different inserts at the tip, offset from each other, with coolant holes in the body. The body is marked with diameter, length ratio and insert code. Spade drills show a single flat blade held by a screw across the slot. The holder is marked with its blade series; the blade is marked with diameter and series.

Insert drill vs spade drill

Feature	Indexable insert drill	Spade drill
Cutting edge	Two indexable inserts	One replaceable blade
Usual depth	Short, about 2 to 5 x D	Short to long series
Hole bottom	Flat	Pointed to the blade angle
Size range per body	One diameter (some allow small offset on a lathe)	One holder fits a range of blade sizes
Coolant	Through the body, needed	Through the holder on most
Machine needs	High power, rigid setup	Rigid setup; less power than insert drill
Hole finish and size	Rougher; may need finishing	Good; blades can be ground to size

Key points

Insert drills need a rigid machine with enough spindle power and torque at the speed used. Check the drill maker's power data.
Coolant through the body is required for insert drills. Chips must be flushed out or the drill breaks.
On a lathe, an insert drill can be offset slightly to make a hole a little larger than nominal. The allowed offset is in the maker's data.
A slug or disc can break free at exit on a through hole. Guard the area.
Spade blades and holders must match the same series. Blades from another series will not seat.

Common mistakes

Running an insert drill in a light machine or a drill press.
Mixing center and outside inserts in the wrong pockets.
Running without through-coolant.
Using worn screws or damaged pockets, which let inserts shift.

Governing standards: No single consensus standard covers indexable drill or spade drill geometry. Insert codes follow ISO 1832 on many inserts. Follow the tool maker's cutting and machine data.

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.

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