# Step drills

Multiple-diameter drill geometries, sheet-metal step bits versus combination drills, axial step length, entry capability and worked diameter, speed and volume calculations.

Reviewed: 2026-11-02

Tags: tooling, cutters, drilling, sheet-metal

An ideal enlargement from **10 to 12 mm** through **2.0 mm sheet** removes **69.12 mm³** of material. At **800 rpm**, the **12 mm step** travels at **30.16 m/min** and the **20 mm step** at **50.27 m/min**. Check actual axial land, starting capability, shank and speed for each step.

Step drills cut multiple diameters on one axis. Gühring distinguishes combination tools for counterbores and core holes from sheet-metal applications. [Gühring, Drilling tools — Step drills](https://guehring.com/uk/products/drilling-tools/)

## Two meanings of a stepped tool

In a **sheet-metal step bit**, advancing the tool brings successively larger cutting steps into the sheet. RUKO distinguishes these fixed diameter stages from a **sheet or peel drill**, which has a continuously conical cutting edge and can leave a slightly tapered hole. Its comparison discusses thin material, up to 4 mm depending on material and tool; that is the article's application scope, not a universal thickness rating for all step drills. The next step can also deburr the preceding hole, although edge treatment and an accurately dimensioned chamfer are different requirements. [RUKO, Step drills vs. sheet drills](https://ruko.de/en/knowledge/know-how/step-drills-vs-sheet-drills/)

In a **combination step drill**, the diameter sequence and axial lengths correspond to the intended stepped-hole profile. Gühring Australia's special-tool range includes carbide step drills for tap drilling and chamfering, with straight or spiral flutes, internal coolant and PVD coating among the available design options. These are application-specific tool configurations, rather than properties established by the name alone. [Gühring Australia, Special Tools — Step Drills](https://guhring.com.au/special-tools/special-tools.html)

The following comparison is explanatory synthesis of those distinctions:

| Geometry | Intended result | Important distinction |
| --- | --- | --- |
| Stepped sheet-metal bit | One selected through-hole diameter in a thin wall | Later steps can enlarge the opening if advanced too far |
| Combination step drill | A prescribed sequence of diameters and axial features | Step lengths form part of the hole geometry |
| Continuous conical sheet drill | Continuously variable enlargement | Entry and exit diameters can differ through the wall |
| Separate drill and counterbore | Features produced in separate operations | Independent tools permit independent feature depths |

## Diameter increment is not axial capacity

The **diameter increment** is the difference between adjacent nominal hole sizes. The **axial length of a step** is the distance available along the tool at that diameter. These quantities are independent: a bit offering small diameter increments does not thereby have long steps.

For an ideal cylindrical land, a sheet can lie entirely within one diameter only when the usable axial land is at least as long as the material thickness. The simplified axial positioning window is `land length − sheet thickness`. Actual cutting transitions, chamfers, edge radii, tool wear and runout reduce the usefulness of this ideal model. At zero nominal window there is no allowance for positioning error; if the wall is thicker than the land, adjacent step geometry overlaps the wall before a uniform full-depth diameter can be obtained. This is a geometric deduction, not a substitute for a manufacturer's material-thickness rating.

A stepped bit also projects below the sheet before the selected diameter reaches the lower face. Backside clearance therefore depends on the preceding smaller steps and tip, not just the sheet thickness. A blind recess and a through-hole in a thin wall present different access conditions.

## Named examples: flutes, shanks and starting capability

Klein Tools **KTSB01** is an HSS bit with an AlTiN coating, two straight flutes and a **3/8-inch hex shank**. Its 13 nominal diameters run from **1/8 to 1/2 inch in 1/32-inch increments**. Klein lists steel up to 16 gauge, wood, plastic and aluminum as applications. The steel-gauge statement is retained as supplied rather than converted into a universal millimeter thickness for every material. A hex shank's size describes the holding interface; it is not the hole diameter or proof of compatibility with every hex holder. [Klein Tools, KTSB01](https://www.kleintools.com/catalog/step-drill-bits/13-step-drill-bit-38-inch-hex-double-straight-flute-18-inch-12-inch)

RUKO's **ULTIMATECUT HSS-Co 5 FLOWSTEP** family provides a contrasting spiral-fluted, two-edge design with a three-face shank. The page separately identifies a **118° point angle** and **90° step angle**: the entry tip and diameter transitions are distinct geometry. Its listed applications include stainless steel, with applicability tied to that named family rather than to every HSS step bit. [RUKO, ULTIMATECUT HSS-Co 5](https://ruko.de/en/products/step-drills/ultimatecut-step-drill-hssco5/)

Starting capability is another independent property. RUKO also catalogs an **HSS step drill without a tip**, including item **101361** with a 12–20 mm range, straight flutes and an 8 mm shank. A tool explicitly lacking a drilling tip is an enlargement example, not evidence that all step drills can start in solid stock. [RUKO, HSS step drill without tip](https://ruko.de/en/products/step-drills/step-drill-reamer-hss/)

## Worked example: size count, cutting speed and removed volume

For the KTSB01's nominal inch sequence, the number of available sizes follows directly from the stated endpoints and increment:

`N = (1/2 − 1/8)/(1/32) + 1 = 13`

There are 12 intervals but 13 diameters because the first diameter is included. This calculation describes the size sequence; it says nothing about axial step lengths.

Use the hypothetical **10.0 to 12.0 mm** enlargement through **2.0 mm sheet**:

`V = π/4 × (12² − 10²) × 2 = 69.12 mm³`

A complete 12 mm opening has volume `π/4 × 12² × 2 = 226.19 mm³`, but the existing hole already accounts for **157.08 mm³**. Counting the full cylinder as newly removed material would overstate this enlargement operation. Burr removal and any edge bevel are excluded.

At a hypothetical **800 rpm**, peripheral cutting speed at the 12 mm step is:

`vc = π × D × n / 1,000 = π × 12 × 800 / 1,000 = 30.16 m/min`

At the same rpm, a 20 mm step has **50.27 m/min** peripheral speed. Thus a fixed spindle speed does not give constant cutting speed as successively larger steps engage.

Finally, an invented **4.0 mm usable cylindrical land** around 2.0 mm sheet leaves an ideal **2.0 mm axial positioning window**. A 5.0 mm wall would exceed that land by 1.0 mm. Neither calculation establishes the capacity of the cited commercial tools, whose actual step dimensions and operating limits are separate data.

## Coverage and limitations

These sources establish tool categories and named examples, not universal feeds, dimensional tolerances, burr-free performance or tool-life multipliers. Hole diameter, roundness, edge finish and positional accuracy are separate outcomes affected by the tool and setup. A coating or substrate designation alone does not establish compatibility with a particular alloy, hardness or production method.

The cited web pages display no issue date in the material reviewed on November 2, 2026. Copyright years and crawl dates are not treated as publication dates. No manufacturer performance multiplier or generic cutting recipe is adopted here.

## Related reference

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