Large-Diameter Metal Drilling

Need a hole larger than your drill chuck would normally allow? Sutton reduced shank drill bits over 1/2 inch give workshops, fabricators, maintenance crews & engineering users a practical way to drill larger diameters while using a reduced shank designed to fit compatible 13mm drill chucks. Sutton's D188 range combines M2 high-speed steel, a 118° standard point & blue surface finish for large-scale boring across suitable metals & other specified materials.

The advantage is built into the design. A reduced shank is smaller than the cutting diameter, allowing selected Sutton drills above 1/2 inch to be held by a compatible chuck without requiring the shank to match the full hole diameter. Metric D188 options use a 12.5mm reduced shank, while imperial sets include drilling diameters up to 1 inch with 1/2-inch shanks.

Larger cutting diameters also change the demands placed on the drill, machine & workpiece. Sutton specifies these reduced-shank drills for slow-speed drilling at 350 RPM or less, making machine capability, workpiece security & drill control important parts of the setup.

Start with the driving equipment through  Drills, then explore  Drill Accessories when the surrounding drilling setup needs attention.

Why Use a Reduced Shank Drill?

Here's the problem it solves.

Suppose the required hole is 18mm, 22mm or 25mm but the drill chuck accepts a maximum shank around 13mm.

A conventional drill with a shank approaching the full cutting diameter may not fit.

A reduced-shank drill changes that relationship by providing a larger cutting diameter with a smaller shank.

That makes the format useful for workshops needing larger holes without moving every job to a completely different toolholding arrangement.

The reduced shank increases chuck compatibility.

It doesn't reduce the cutting diameter.

Larger Hole, Smaller Shank – Keep the Measurements Separate

A 20mm reduced-shank drill isn't a 20mm shank.

That's an important distinction when choosing tooling.

For metric Sutton D188 reduced-shank drills, the cutting diameter can exceed the shank diameter while the reduced section remains suitable for a compatible 13mm chuck.

Think of the tool as two dimensions:

Cutting diameter = the hole being produced

Shank diameter = the portion being held by the drill chuck

Confusing those measurements can result in the right hole size arriving with the wrong assumptions about how the drill will be held.

What Makes Sutton D188 Reduced Shank Drills Different?

Several features work together in the D188 format.

No single specification tells the whole story.

Diameter, material, speed, chuck capacity & workpiece stability all meet at the same hole.

What Materials Can Sutton Reduced Shank Drills Cut?

Steel is an obvious application, but it isn't the only material suited to the range.

Depending on the individual drill & application, Sutton D188 reduced-shank drills can be used across suitable:

► Steel
► Aluminium
► Copper & brass
► Cast iron
► PVC plastic

The blue surface finish is particularly relevant to ferrous applications, helping support drilling in materials such as low-carbon steel.

Material still matters.

A setup that performs well in steel shouldn't automatically be copied unchanged into aluminium, brass or cast iron simply because the same drill diameter is being used.

Why Does Sutton Specify Low-Speed Drilling?

Diameter changes cutting conditions.

As drill diameter increases, the outside cutting edge travels further during every spindle revolution.

That means a large drill doesn't necessarily want the same RPM as a small jobber drill.

Sutton specifies 350 RPM or less for its reduced-shank range.

Treat that as a maximum rather than an instruction to run every material & diameter at exactly 350 RPM. Suitable operating conditions still depend on the drill diameter, work material, machine capability & cutting setup.

Big drills reward controlled speed.

Example: Drilling a 20mm Hole Through a Steel Bracket

Picture a fabrication repair where a substantial steel bracket needs a 20mm clearance hole.

The workshop has suitable drilling equipment with a compatible 13mm chuck.

A 20mm Sutton reduced-shank drill allows the cutting diameter to exceed the chuck's nominal capacity because the tool steps down to a smaller shank.

Before drilling:

► Confirm the finished hole diameter.
► Check the chuck can correctly accept the reduced shank.
► Secure the bracket.
► Establish the hole position.
► Select suitable drilling speed & cutting conditions.
► Keep the drill aligned as the larger cutting edges engage.

The reduced shank solves the holding problem.

The operator still has to solve the drilling problem.

Enlarging an Existing Hole? Check Before Cutting

Already have a smaller hole?

Don't automatically assume the larger reduced-shank drill can simply be pushed through under the same conditions used for drilling solid material.

An existing hole changes how the cutting edges engage.

How much material remains, whether the existing hole is centred & how the larger drill first contacts the workpiece can all influence the operation.

Assess the existing feature before proceeding.

When finished dimensions matter,  Calipers (Digital / Manual) can support measurement before & after drilling.

Larger Diameters Put More Attention on Workholding

A large drill can generate substantial torque.

If the workpiece is free to move when the cutting edges bite, the component can become part of the rotating system.

That's not a useful feature.

Secure the workpiece & drilling equipment appropriately before beginning the cut.

For bench-based drilling where suitable workholding is required,  Clamps & Vises provides a practical path into workshop holding equipment.

Secure first.

Drill second.

Why M2 High-Speed Steel?

Reduced-shank drills still need cutting material suited to demanding workshop use.

Sutton manufactures the D188 range from M2 high-speed steel, combining strength, heat resistance & wear resistance for general-purpose drilling across suitable materials.

That makes HSS a practical choice for larger-diameter workshop drilling.

It doesn't mean cutting conditions can be ignored.

Excessive speed, poor chip clearance, unstable workholding or damaged cutting edges can still compromise the result.

Tool material supports the process.

It doesn't replace it.

What Does the 118° Point Do?

At the front of the D188 sits a 118° standard point.

This is a general-purpose drilling geometry suited to the broad workshop role of the reduced-shank range.

Point geometry is still only one part of drilling behaviour.

Material, drill diameter, feed, speed, lubrication where appropriate & machine rigidity all influence what happens once the cutting edges enter the workpiece.

Metric or Imperial? Check the Job Before the Drill Drawer

“Close enough” becomes less convincing as hole size starts affecting fit.

Sutton reduced-shank tooling is available across metric & imperial sizes, including metric diameters above 13mm & imperial options extending beyond 1/2 inch.

Choose the measurement system specified by the component or job.

Don't substitute a nearby metric diameter for an imperial requirement—or the other way around—without checking how the resulting clearance affects the assembly.

A fastener, pin, bush or mating component only cares about the hole it receives.

Reduced Shank or Taper Shank?

Both formats can solve larger-hole drilling requirements, but they connect to the machine differently.

If the workshop already has suitable taper drilling equipment, a taper-shank drill may belong in that process.

When the job calls for a larger cutting diameter through a compatible 13mm chuck, reduced-shank tooling solves a different problem.

Choose from the machine outward.

Should You Drill a Pilot Hole First?

Not every large hole automatically needs a pilot.

Pilot-hole requirements depend on the drilling setup, material, diameter, machine, existing feature & method being used.

An unnecessary pilot can alter how the cutting edges engage just as surely as a useful pilot can assist a particular drilling process.

Avoid turning workshop habit into a universal rule.

Assess the hole you're actually producing.

Watch the Chips – They Tell You What's Happening Inside the Hole

Once the cutting edges enter the material, much of the important action disappears from view.

The swarf coming back out doesn't.

Watch chip formation & evacuation during drilling.

A noticeable change can indicate altered cutting conditions, material behaviour, a deteriorating cutting edge or restricted chip clearance.

Stopping to investigate unusual cutting behaviour takes less time than recovering from damaged tooling or a damaged workpiece.

For preparation & finishing around fabrication work,  Metal Cutting & Grinding Tools provides a useful connection to the surrounding metalworking process.

Five Questions Before Fitting a Large Reduced-Shank Drill

What Diameter Does the Finished Hole Need?

Start with the component requirement—not the nearest drill in the cabinet.

Will the Reduced Shank Fit the Chuck Correctly?

Confirm chuck capacity & tool-shank diameter before switching the machine on.

What Material Is Being Drilled?

Steel, aluminium, brass, cast iron & plastic don't all behave identically.

Is the Workpiece Properly Restrained?

Large-diameter drilling can generate meaningful torque. Workholding deserves attention before cutting starts.

Can the Machine Run the Required Low-Speed Operation?

Sutton specifies 350 RPM or less for this range. Confirm the equipment can operate appropriately for the job.

Five answers now can prevent a sixth question later:

What went wrong?

Practical Tips for Large-Diameter Reduced-Shank Drilling

Confirm both diameters. Cutting diameter & shank diameter perform different jobs.

Check chuck capacity before ordering. Reduced doesn't mean universally compatible.

Respect the low-speed requirement. Sutton specifies 350 RPM or less for the D188 reduced-shank range.

Secure the component firmly. Larger drilling diameters can generate greater torque at the workpiece.

Keep the drill aligned. Side loading doesn't become useful just because the cutter gets bigger.

Match conditions to the material. Steel, aluminium, brass & cast iron shouldn't automatically receive identical treatment.

Watch the chips. Changes in swarf can provide an early warning that the cutting process has changed.

Avoid unnecessary projection. Hold the drill securely without extending more tool than the operation requires.

Inspect the cutting edges. A large drill with damaged lips won't improve because the machine has more power.

Measure the result. Where diameter matters to an assembly, verify the finished feature rather than assuming nominal drill size tells the entire story.