How To Enlarge a Hole

Hole enlargement is often necessary when upgrading or replacing hardware, fixtures, or components that need a larger opening than what currently exists. Typical projects include upgrading door locksets, installing larger electrical outlets, or modifying plumbing fixtures. Before you grab a drill or saw, there are proper techniques and tools to use when enlarging holes to avoid damaging your surfaces and to get a professional finish. This guide will help you enlarge holes safely and carefully so you can tackle a range of home improvements.

Essential Tools for Enlarging Holes

Let’s explore the primary tools you’ll need to enlarge holes based on the materials and project:

• Power drill: Choose a power drill with variable speed settings and enough power to handle the materials you’ll be working with.
• Hole saw: Hole saws are circular cutting tools that attach to your drill. They come in different sizes and are particularly useful for enlarging existing holes. Bi-metal hole saws are best for metal enlargement tasks, while carbide-tipped hole saws are better for wood and plastic.
• Step drill bits: Step drill bits are conical in shape with multiple cutting edges of increasing diameter. These are best for gradually enlarging holes in thin materials like sheet metal or plastic.
• Hole enlarging reamers: Hole enlarging reamers gradually shave material from the interior of the hole, creating a smooth, accurate enlargement. These tools are commonly used in metalworking but can also be applied in woodworking and plastic work.

Safety Precautions When Enlarging a Hole

Always prioritize safety when working with power tools. Wear appropriate personal protective equipment, including safety glasses, work gloves, and hearing protection. Keep your work area well-lit and free from clutter. If working with metal, be cautious of sharp edges and hot shavings. Additionally, secure or weigh down the materials while you’re working to prevent movement during drilling.

Pro Tip: Tom Silva, This Old House general contractor, stresses the importance of choosing the right protective equipment: “When it comes to protective equipment, I choose what fits and allows me to move easily.” Besides comfort and fit, he recommends checking the performance rating on any safety gear before you buy it.

When enlarging a hole in steel, be especially mindful of bit condition. As Norm Abram advises, trying to muscle a dull bit through metal will cause it to overheat, lose its temper, and stop cutting. Wear safety glasses—a spinning bit can send hot metal shavings flying. It also helps to squirt a few drops of oil on the surface to lubricate and cool the bit.

Even seasoned pros respect the force of a power drill. Tom Silva recalls a time when a knot stopped his bit cold, and the drill swung counterclockwise, carrying his hand through adjacent drywall before he could release the trigger. His lesson: always brace yourself with a wide stance and hold tight to an auxiliary handle, the longer the better. High-torque drills will get the jump on inattentive drillers, so never let your guard down when enlarging a hole.

Measuring and Marking a Hole

Use a ruler or caliper to accurately measure the existing hole and the required new size. Mark the center of the existing hole and, if necessary, draw a circle to indicate the new hole size. Use a permanent marker for materials like metal and plastic, and a pencil or chalk for wood or masonry.

Step-By-Step Guide To Enlarge an Existing Hole

Here are some different methods for enlarging holes based on the materials you’re working on. 

Double Hole Saw Method

This technique is handy for enlarging door holes for doorknobs, deadbolts, and other locksets or working through other thick materials. It also minimizes the risk of damaging the surrounding material. Here’s how to do it:

1. Select two hole saws—a larger one for the new hole size and a smaller one that fits the existing hole.
2. Mount both hole saws on a single arbor, with the smaller saw protruding at least half an inch beyond the larger one.
3. Insert the smaller saw into the existing hole.
4. Carefully guide the drill, keeping it steady and straight as the larger saw cuts the new hole around the existing one.
5. After cutting, check the hole for smoothness and use a file or sandpaper file down any rough edges.

Step Drill Bits

These bits are great for enlarging holes in thinner materials, such as sheet metal work and plastic paneling in car bodies and appliance cases.

1. Start with the smallest step that fits into the existing hole.
2. Apply steady pressure and drill slowly, allowing the bit to gradually make the hole bigger.
3. Continue until you reach the desired hole size, indicated by the appropriate step on the bit.
4. Remove any burrs with a deburring tool or sandpaper and make sure it is uniform and smooth.

Using a File or Rasp

For minor enlargements or when working with softer materials like plastic, wood, and soft metals, a file or rasp can be effective:

1. Select a round file or rasp that fits the existing hole.
2. Work the file around the circumference of the hole, applying even pressure.
3. Regularly check your progress and aim for a smooth, circular enlargement.
4. Clean up any rough edges with sandpaper.
5. If needed, switch to a finer file for the finishing touches.

Hole Enlargement Using Hand Tools

Sometimes, you may need to make a hole bigger without access to power tools. Here are two manual methods.

Manual Reaming

A hand reamer is a precision tool that can gradually enlarge holes and is especially suitable for metal or fine woodworking:

1. Choose a reamer slightly larger than the existing hole.
2. Insert the reamer into the hole and turn it clockwise with steady pressure.
3. Continue until you reach the desired size, periodically removing the reamer to clear debris.
4. Check the size frequently to avoid over-reaming.

Sandpaper Method

This method is efficient for making slight enlargements or cutting into softer materials like drywall, wood, and certain plastics.

1. Wrap a dowel or pencil with coarse-grit sandpaper.
2. Insert the wrapped dowel into the hole and rotate it to sand the edges.
3. Gradually work up to finer grits for a smooth finish.
4. Keep checking the hole to make sure your enlargement is even.

Hole Expansion Troubleshooting and Tips

Here’s how to address common issues you may face with hole enlargement:

Dealing with Uneven Edges

If your enlarged hole has rough or uneven edges:

1. Use a deburring tool or fine-grit sandpaper to smooth the edges.
2. For metal, a file can help achieve a clean finish.
3. In wood, a sanding block or drum sander attachment for your drill can even out the hole’s circumference.
4. Continuously check the hole for smoothness and sand as needed.

Enlarging Irregularly-Shaped Holes

If you need to make an oddly-shaped hole bigger:

1. Use a rotary tool with a sanding attachment or a file to gradually enlarge the hole following your desired shape.
2. Continuously check the hole against your template or required component to make sure it fits.
3. Make final adjustments using fine-grit sandpaper or a small file to smooth any remaining rough spots and perfect the shape.

If you overshoot: Should you accidentally enlarge a hole too much, you can recover by filling it with a custom-cut plug. TOH master carpenter Norm Abram advises orienting the grain of the plug so it lines up with the surrounding wood grain, then gluing it in place with yellow woodworker’s glue. Once dry, plane or sand the plug flush, fill any gaps with wood filler, and refinish. Then re-drill or re-cut your hole at the correct size.

Preventing Damage

To avoid splintering or cracking:

Pro Tip: Tom Silva, TOH general contractor, always clamps a backup scrap behind the workpiece when drilling: “It’s the bit that makes the drill look good,” he says. Whenever he picks up a bit, he looks for nicks, rounded edges, and the blue discoloration indicating lost temper. He grazes his fingertips over the bit’s edges to test sharpness. “If it’s not in good shape, I won’t use it,” he says.

1. When drilling wood, place a scrap piece behind the workpiece to prevent tear-out.
2. Use masking tape over the cutting area to reduce chipping for plastics or laminates.
3. Always drill at the appropriate speed for your material—slower for harder materials, faster for softer ones.
4. When drilling metal, use lubricant, such as cutting oil, to reduce heat and wear on the bits.

For steel: To prevent the bit from skating around at the start, use a center punch to make a small dimple in the surface, then add a drop of oil to the dimple to lubricate the bit and keep it cool. As Norm Abram advises, apply light to moderate pressure—trying to muscle the bit will cause it to overheat, lose its temper, and stop cutting. If progress is slow, first drill a smaller hole before stepping up to the final size.

Keep Everything Even

For even enlargement:

1. Start at a slow drill speed to establish the hole and then incrementally increase the speed.
2. Apply consistent pressure to prevent the drill from jerking or “wandering.”
3. Periodically pause to clear out debris, allowing for a smoother, more even cut.

When enlarging holes in wood, sap and debris can pack into the bit’s flutes, causing it to bind and overheat. As TOH host Tommy explains, “You’ve got to back it out, clean the wood off, push it back in. But when you do that, you gotta be careful because these get very hot.” He also recommends varying your speed as you work: “In some cases, you’re gonna wander up and down with your speed and work it.”

Choosing the Right Tool for the Material

Different materials require different tools and techniques:

• For wood, use sharp bits and slower speeds to avoid burning.
• Metal requires lubricated, high-speed drilling with cobalt or titanium bits.
• Plastic benefits from moderate speeds and gradual pressure to prevent melting or cracking.
• Fiberglass requires special care due to its composite nature. Use carbide-tipped bits at moderate speeds to avoid overheating and damaging the material.
• For masonry, concrete, or brick, use masonry bits with a hammer drill function to get through the surface without damaging the surrounding area.