How To Drill Through Sheet Metal
Content Menu
● Material Behavior During Drilling
● Clamping and Workpiece Support
● Speed, Feed, and Peck Strategy
● Tool Maintenance and Sharpening
● Common Shop Mistakes and Fixes
● Q&A
Introduction
Most people in manufacturing shops treat drilling sheet metal like a routine job—grab a bit, spin the drill, and move on. But anyone who’s dealt with warped panels, torn edges, or bits that dull after ten holes knows there’s more to it than that. Getting clean, accurate holes in sheet metal consistently takes attention to material behavior, tool choice, speeds, feeds, and a handful of small tricks that separate decent work from production-grade results.
This article walks through the process step by step, pulling from real shop experience and several peer-reviewed studies on drilling mechanics. The goal is straightforward: help manufacturing engineers, fabricators, and toolroom people reduce scrap, extend tool life, and produce holes that don’t need extra cleanup or rework. We’ll cover everything from picking the right bit to advanced options like friction drilling, with plenty of concrete examples drawn from automotive, HVAC, enclosure work, and structural fabrication.
Sheet metal drilling problems usually fall into a few categories: the bit walks at the start, the hole comes out oversized or oblong, exit burrs are excessive, the material distorts, or the tool overheats and fails early. Each issue has practical fixes, and many of them come down to understanding how different alloys react under cutting forces and heat.
Material Behavior During Drilling
Different sheet metals respond differently when a rotating bit pushes through them. Mild steel (typically A36 or similar) work-hardens noticeably if feed is too slow or if the bit starts to rub instead of cut. That hardening makes the next pass even tougher, which is why dull tools create a vicious cycle.
Aluminum alloys (5052, 6061, etc.) are softer but much more ductile. They tend to smear and build up on the cutting edges unless chip evacuation is good and some lubricant is present. Stainless grades (304, 316) combine high work-hardening with poor thermal conductivity, so heat builds quickly and stays in the cutting zone—exactly the conditions that kill HSS bits fast.
Thickness plays a big role too. Below about 0.040 in (20 gauge), sheets flex easily, so clamping pressure and support underneath become critical. Above 0.125 in (1/8 in), you start needing more torque and often a pilot hole strategy to keep forces manageable.
One practical case: a shop making electrical enclosures from 16-gauge mild steel kept getting oblong holes on the corners. They traced it back to insufficient clamping—the sheet vibrated just enough to let the bit wander. Switching to a heavier fixture with side supports fixed it immediately.
Another example comes from an HVAC contractor drilling 5052 aluminum for duct fittings. Without cutting fluid the aluminum balled up on standard HSS bits after only a few holes. A quick switch to a light mist of soluble oil doubled tool life and left much cleaner exits.
Bit Selection and Geometry
Bit choice drives almost everything else. High-speed steel (HSS) twist drills remain the baseline for mild steel and aluminum under moderate production volumes. For stainless or repeated heavy use, cobalt (M35 or M42) or carbide-tipped bits pay for themselves quickly.
Point geometry matters more than most people realize. Standard 118° points are fine for general work, but 135° split-point or four-facet points reduce the “walking” tendency dramatically, especially on flat, unmarked surfaces. The split-point design creates a positive rake at the very center, so the bit starts cutting instead of skating.
Helix angle also influences performance. Standard 30° helix works well across most metals, but higher-helix (around 38–45°) bits clear softer aluminum chips more aggressively, while lower-helix bits give better support in harder steels.
Real-world comparison: a fabricator doing custom brackets in 304 stainless tried standard HSS bits and burned through three in a single shift. Switching to 8% cobalt bits with split points let him finish the job with one bit and noticeably less heat at the hole.
For very thin material (<0.032 in), step drills or sheet-metal-specific unibits often outperform twist drills because they enlarge the hole gradually and create almost no exit burr.
Clamping and Workpiece Support
Loose clamping is responsible for more bad holes than almost any other single factor. When the sheet can lift or vibrate, the drill bit follows the movement instead of staying perpendicular, producing elongated or multi-sided holes.
Use toe clamps, step blocks, or magnetic fixtures whenever possible. For non-ferrous metals, vacuum tables or double-sided tape combined with edge clamps work well. Always put a sacrificial backer—usually MDF, plywood, or even a piece of scrap steel—under the workpiece. The backer supports the exit side and drastically reduces tear-out burr.
Example from a job shop building machine guards: they drilled 11-gauge galvanized steel panels. Early attempts without a backer left huge exit burrs that required 15–20 seconds of deburring per hole. Adding 3/4 in plywood underneath dropped deburr time to almost nothing.
Speed, Feed, and Peck Strategy
Manufacturers publish recommended surface feet per minute (SFM) and chip loads, but real shop conditions often force adjustments. As a rough guide:
- Mild steel: 80–120 SFM
- Aluminum: 200–400 SFM
- Stainless: 40–80 SFM
Feed rate is usually 0.002–0.006 in per revolution for small bits, scaling down as diameter increases.
Peck drilling—advancing a short distance, then fully retracting to clear chips—becomes almost mandatory in holes deeper than about 3× diameter. Without pecking, chips pack the flutes, heat skyrockets, and the bit either binds or burns.
A concrete case: drilling 0.250 in holes through 0.120 in 6061 aluminum for rivet mounting. At constant feed the chips balled up after four or five holes. Switching to peck every 0.100 in with full retraction cleared the flutes reliably and kept the same bit sharp for over 300 holes.
Lubrication Choices
Dry drilling works in some cases—especially with coated carbide bits—but most production shops see better results and longer tool life with some form of coolant or lubricant.
- Soluble oil emulsions (5–10%) → general-purpose choice for steel and aluminum
- Straight cutting oil → tougher steels and stainless
- WD-40 or similar light penetrating oil → occasional aluminum work
- Minimum quantity lubrication (MQL) mist → high-volume lines trying to reduce mess and disposal costs
One fabricator making aluminum battery trays switched from dry to MQL and saw tool life increase by roughly 60%. The mist kept temperatures down without flooding the machine.
Burr Formation and Control
Entry burrs usually come from excessive feed or a dull bit; exit burrs are more common and harder to eliminate completely.
Ways to reduce exit burr:
- Sharp bits with proper relief angles
- Backing material that supports the exit side
- Slightly lower feed on the final 0.020–0.030 in of cut
- Chamfer or countersink the hole immediately after drilling
In high-spec work (aerospace brackets, medical enclosures), shops often use a secondary chamfer pass with a 90° or 82° countersink bit to break the edge cleanly.
Friction Drilling Overview
Friction drilling (also called thermal drilling or form drilling) deserves its own section because it changes the game for certain applications. Instead of removing material, a hard carbide tool spinning at high speed generates frictional heat that softens the sheet. The material flows plastically upward, forming a bushing 2–3 times the original thickness. That bushing can then be threaded directly.
Advantages:
- No chips
- Stronger hole (the displaced material work-hardens)
- Excellent for thin-to-medium gauges (0.030–0.250 in)
- Works well on coated steels because the coating melts away locally
Limitations:
- Requires higher spindle power
- Tool geometry is specific and expensive
- Not ideal for very thick material or hardened alloys
A manufacturer of office furniture frames switched from conventional drilling + insert nuts to friction drilling on 1.5 mm mild steel. They eliminated a secondary tapping operation and gained a stronger thread engagement. Cycle time dropped noticeably.
Another application: automotive exhaust hangers. Friction-drilled holes in stainless tubing accept self-tapping fasteners without weld nuts, cutting weight and assembly steps.
Tool Maintenance and Sharpening
Even the best bit dulls eventually. Watch for:
- Increased feed force
- Poor chip color (bluish or black instead of silver)
- Smoke or discoloration around the hole
- Rough hole walls
Most shops send HSS and cobalt bits out for professional sharpening rather than attempting it in-house. Carbide bits are usually run until failure because regrinding is uneconomical.
Keep a log of holes per bit—it quickly shows when a process change (speed, feed, lube) makes a measurable difference.
Common Shop Mistakes and Fixes
- No center punch or pilot hole → wandering → use automatic center punch or start with 1/8 in pilot
- Excessive pressure on hand drills → flexing → switch to drill press or magnetic drill whenever possible
- Ignoring helix direction on reversible drills → poor chip evacuation → always forward for right-hand bits
- Drilling coated galvanized without removing zinc first → rapid dulling → spot-grind or chemically strip the coating locally
Wrapping Up
Drilling sheet metal looks simple until you start chasing tolerances, surface finish, and tool costs. The difference between acceptable and excellent work usually comes down to five things: sharp appropriate bits, rigid fixturing with good backing, realistic speeds and feeds, effective chip clearing (pecking or coolant), and attention to heat management.
The examples throughout—electrical enclosures, HVAC ducts, furniture frames, automotive brackets—show that small, deliberate changes deliver outsized improvements in quality and efficiency. Friction drilling opens new possibilities when threaded holes in thin material are needed without added hardware.
Keep experimenting within safe limits, measure results, and adjust. The shop floor teaches faster than any textbook, but starting with proven parameters from research and real applications gives you a solid baseline to improve from.
Q&A
Q: Which bit lasts longest in 304 stainless sheet?
A: 8% cobalt (M42) split-point bits usually outperform standard HSS by a large margin.
Q: How do I stop thin aluminum from tearing on exit?
A: Clamp tightly, use a wood or phenolic backer, and take light cuts with mist lubricant.
Q: Is friction drilling worth the tool cost for low-volume work?
A: Usually not—conventional drilling + tapping is cheaper unless you need many threaded holes in thin material.
Q: What spindle speed should I run for 1/4 in holes in mild steel?
A: Around 800–1200 RPM depending on bit condition and machine rigidity; start conservative and watch for heat.
Q: Can I drill pre-painted sheet metal?
A: Yes, but expect faster dulling; remove paint at the spot with a countersink or abrasive first if possible.