How to Enlarge an Existing Hole in Metal Safely
By Quality Industrial Abrasives and Tools | Benchmark Abrasives | Published: 2026-10-16
Category: How-to Guides
Enlarging a hole in metal is safer when you support the bit, control speed, and step up in small increments. Here is the order that prevents grab, chatter, and ruined work.
Quick answer
To enlarge an existing hole in metal, clamp the workpiece, start with a bit or cutter that fits the current hole, and increase diameter in small steps rather than jumping to the final size. Use a step drill bit for thin sheet and a hole saw for larger diameters in plate, and keep speed low with steady pressure so the cutter does not grab.
Why the first bite decides the outcome
An existing hole gives the cutter nothing to center on, so the tool tends to walk, grab, or chatter the moment it touches metal. The fix is to create a controlled starting point: clamp the work so it cannot move, and let the cutter enter with light, even pressure instead of forcing it. If the hole is already larger than the pilot, use a step drill bit or a hole saw whose pilot fits the current opening, or clamp a scrap plate with a correctly sized hole over the work as a guide.
Match the cutter to the material and final size
Thin sheet metal, electrical boxes, and tubing enlarge cleanly with a step drill bit because the stepped flutes cut a series of small increments and leave a burr-free edge in aluminum, copper, plastic, sheet metal, and carbon fiber. Thicker plate, wood-backed assemblies, and diameters beyond what a step bit reaches call for a hole saw, which removes a plug and handles larger sizes in one pass. For cleaning up or slightly opening a hole that is already close to size, a carbide burr in a die grinder removes material gradually and lets you sneak up on the final dimension.
Speed, pressure, and lubrication
Run the drill slower than you would for a fresh hole. High speed with light feed glazes the cutting edge and work-hardens stainless, while too much feed on a step bit can snap the pilot. Use cutting fluid or a few drops of oil on steel, keep the drill perpendicular to the surface, and let the cutter do the work. If you hear squealing or see the bit stalling, stop, reduce speed, and check that the workpiece has not shifted.
Steps to enlarge a hole safely
- Clamp and support the workpiece: Secure the metal to a bench or drill press table so it cannot spin or lift. Back the exit side with scrap wood to reduce burrs and support the cutter as it breaks through. Checkpoint: if the part moves by hand, it will grab when the cutter bites.
- Pick a cutter that matches the current hole: Use a step drill bit when the existing hole is smaller than the first step, or a hole saw with a pilot that fits the current opening. For a hole already near final size, use a carbide burr to open it gradually. Mistake to avoid: forcing a pilot that is larger than the hole, which lets the cutter wander off center.
- Increase diameter in small increments: Open the hole one step or one size at a time rather than jumping to the final diameter. Let the cutter cool between passes and clear chips before the next step. Mistake to avoid: skipping sizes, which overloads the cutter and can snap a step bit or stall a hole saw.
- Control speed and feed: Run slower than a fresh-hole cut, apply steady pressure, and use cutting fluid on steel. Keep the drill perpendicular so the hole stays round. Mistake to avoid: high speed with light feed, which glazes the edge and work-hardens stainless.
- Deburr and check the final size: After the last pass, remove the burr with a deburring tool or light pass with a carbide burr. Test-fit the fastener or pipe before calling the job done. Checkpoint: if the fastener still will not pass, open the hole one more small increment rather than forcing it.
Tools that fit this job
- 1-3/8" Bi-Metal Holesaw: 1-3/8" (35MM) bi-metal holesaw, made in USA, 4/6 TPI with positive rake angle, side cut-outs for debris and plug removal. The coarse 4/6 TPI and positive rake clear chips quickly in wood and metal, and the side cut-outs let you pop the plug without prying the saw out of the hole.
- USA Made Titanium Step Drill Bit 9/16"-1" (8 Steps): USA made titanium step drill bit, 9/16"-1" in 8 steps, titanium nitride coated, two-flute design for burr-free holes in aluminum, wood, copper, plastic, sheet metal, and carbon fiber. The stepped sizes let you open a hole in controlled increments instead of one aggressive cut, which is exactly what prevents grab when the pilot has nothing to follow.
- #9 HSS Black Oxide Jobber Length Drill Bit - 12 Pack: #9 HSS black oxide jobber length drill bits, 12 pack, long length relative to diameter for more flexibility and shock absorption than cobalt, powdered-metal, or carbide jobber bits. A pack of the same size lets you replace a dulled bit mid-job, and the flexibility helps absorb vibration when you are drilling out an existing hole by hand.
