# Indexable drills

Replaceable-insert drill bodies, central and peripheral cutting roles, chip evacuation and the limits of nominal hole data.

Reviewed: 2026-11-02

Tags: tooling, drilling, indexable-inserts, holemaking

An ideal **20 mm indexable drill** at **1,000 rpm** and **0.15 mm/rev** feeds **150 mm/min** without an additional factor for insert count. **60 mm** of steady cylindrical cutting takes **24 s** at **47.124 cm³/min**. Verify the body's feed convention, insert seats, usable depth and chip evacuation.

An indexable drill uses replaceable inserts in a reusable body. Many designs divide the cut between central and peripheral inserts.

This reference concerns indexable-insert drills, often called U-drills in shop usage. It distinguishes them from solid drills and exchangeable-tip or modular-head systems. These categories can overlap in commercial terminology, so a product's actual construction matters more than its shorthand name.

## Body, inserts and cutting roles

| Construction | Cutting element and interface |
| --- | --- |
| Solid drill | Cutting edges are part of the drill itself; reconditioning depends on the tool |
| Indexable-insert drill | Separate inserts seat in pockets in a reusable body |
| Exchangeable-tip drill | A replaceable tip carries the drill-point geometry across the diameter |
| Modular drilling assembly | Can include exchangeable heads, bodies or extensions; the name alone does not define the cutting arrangement |

Sandvik's drilling guidance distinguishes central and peripheral chips in indexable-insert drilling: the central insert produces a recognizable conical chip, while the peripheral insert produces a turning-like chip. This reflects their different cutting regions, not interchangeable roles for every insert in every body. [Sandvik drilling tips](https://www.sandvik.coromant.com/en-gb/knowledge/drilling/drilling-tips)

**Explanatory synthesis:** circumferential speed varies with distance from the drill axis. The center region and outer diameter therefore experience different speed conditions at the same spindle speed. Insert geometry, grade, edge preparation and location can consequently differ. A compatible screw hole or similar external shape does not establish that an insert is suitable for a particular pocket.

The insert seat, supporting surfaces and retention components are also part of the cutting system. An undamaged cutting edge does not compensate for a damaged seat, contamination beneath an insert or inadequate body support. Indexability is a maintenance and tooling-economy characteristic, not a guarantee of a particular hole tolerance.

## A bounded model example

Sandvik's product page for **880-D6000L40-02**, material ID **5765549**, lists a **60 mm cutting diameter**, **120.9316 mm usable length**, **0.9316 mm point length** and **40 mm connection diameter**. It identifies one **880-090608H-C-GM** central-type insert and one **880-0906W08H-P-GM** peripheral-type insert. The listed face-effective cutting-edge count is **1**, despite two cutting items. These are fields for this specific body, not dimensions or insert choices for the whole category. [Sandvik 880-D6000L40-02 product data](https://www.sandvik.coromant.com/en-gb/product-details?c=880-d6000l40-02)

**Explanatory synthesis:** insert count is not automatically the multiplier used in a feed calculation. If cutting data are supplied as feed per revolution, multiplying them again by the number of inserts changes their meaning. Point length, usable length, body length and overall length are likewise separate dimensions. A depth ratio without its dimensional definition is insufficient to establish full-diameter depth or breakthrough clearance.

ISCAR's DR-TWIST application page describes bodies accommodating **two to four square inserts**, with **four cutting edges per insert**, twisted flutes and coolant holes. It describes selecting chipbreakers and grades for the application. This is a family-specific construction example; four available edges do not establish four times the life in every operation or equal wear at every insert position. [ISCAR DR-TWIST drilling application](https://www.iscar.com/newarticles.aspx/countryid/29/newarticleid/363)

## Hole depth, entry and exit conditions

A drill that performs well on a perpendicular solid entry can behave differently at a sloped face, cross hole, interrupted cut or uneven exit. Cutting forces change as different portions of the edge enter and leave the material. Rotating-tool drilling and a stationary drill in a rotating workpiece also have different alignment arrangements.

ISCAR's DR technical sheet distinguishes irregular entry or exit, interrupted cutting and stacked plates rather than treating them as ordinary drilling. It also separates troubleshooting for rotating and non-rotating drills and discusses insert overlap, alignment and chip behavior. Its particular corrective settings are not universal settings for other drill systems. [ISCAR DR technical sheet](https://www.iscar.com/eCatalog/Ecat/datafileENM/INFO/DR.pdf)

**Explanatory synthesis:** a pre-hole is not automatically beneficial. It changes which insert regions carry load and how the body is supported by the cut. Pilot holes, spot drilling, pecking and offset drilling are application-specific operations; an indexable body is not automatically approved for each of them. Nor does an adjustable or offset drilling capability imply that arbitrary side milling or boring is permitted.

Thin workpieces and weak clamping can deflect under thrust. At breakthrough, remaining material support changes, and an exit burr or disc can create additional problems. A through-hole cycle therefore includes geometry and travel beyond the nominal plate thickness.

## Coolant and chip evacuation

Sandvik's drilling guidance relates chip evacuation to workpiece material, insert geometry, cutting data and coolant pressure and volume. It notes that chip jamming can move the drill radially, damage the hole surface and cause insert or drill breakage. Internal delivery is particularly favored for deeper holes and long-chipping materials; pressure alone does not describe delivered flow. [Sandvik drilling tips](https://www.sandvik.coromant.com/en-gb/knowledge/drilling/drilling-tips)

**Explanatory synthesis:** the machine pump rating is not necessarily the flow reaching the cutting zone. Passages, holder connections, filters and restrictions affect delivery. A chipbreaker intended for one feed or material range may not form evacuable chips under another condition. Very long chips and a congested stream of short chips can present different evacuation problems, so “small chips” alone does not prove a stable process.

Coolant compatibility includes the tool, workpiece, fluid and machine. No universal pressure, concentration, dry-drilling allowance or peck cycle follows from the word indexable.

## Original example: feed, time and local speed

Use the example’s hypothetical diameter, feed per revolution and speed over **60 mm** of steady travel. Exclude entry, acceleration, breakthrough, dwell and retract.

```text
Axial feed = 0.15 × 1,000 = 150 mm/min
Ideal cutting time = 60 / 150 = 0.4 min = 24 s

Full cylindrical volume = pi/4 × 20² × 60
                        = 18,849.6 mm³ = 18.8496 cm³
Ideal removal rate = 18.8496 / 0.4 = 47.124 cm³/min

Outer-diameter surface speed = pi × 20 × 1,000 / 1,000
                             = 62.832 m/min
At radius 5 mm: surface speed = 31.416 m/min
```

The point at half the outer radius has half the circumferential speed. At the mathematical axis the rotational speed contribution is zero; this does not mean the central insert performs no cutting or experiences no load.

The cylindrical volume excludes the point profile. Verify actual torque, power, chip form and cycle time. An existing hole changes removal volume and engagement.

## Finished-hole and source limits

**Explanatory synthesis:** nominal drill diameter is not a complete finished-hole specification. Diameter variation, roundness, straightness, position, surface texture and exit condition describe different outcomes. Insert wear, body deflection, runout, alignment and workpiece support can affect them independently. A drilled hole can require subsequent boring, reaming or another finishing process when the required result exceeds the drilling process's demonstrated capability.

The cited live Sandvik and ISCAR pages displayed no verified issue date in the versions reviewed on **2 November 2026 PST**. Sandvik's model page includes a product-release field; that is not treated as the revision date of its current data. The one-page ISCAR DR sheet had no verified issue date. This reference adopts no historical catalog settings, universal hole tolerance or manufacturer-wide material guarantee.

## Related reference

[Cutting tools and tooling references](../index.md)