How to Drill and Tap a Hole in Metal: Step-by-Step Guide
Learn a practical, step-by-step method to drill and tap a hole in metal. Choose the right drill size, prepare the work, apply lubricant, and verify threads for clean, durable results.
By the end of this guide you will successfully drill and tap a hole in metal. You’ll choose the correct drill bit and tap size, drill a precise pilot hole, and cut clean threads with the right tapping fluid. The process emphasizes workholding, deburring, lubrication, and safety to prevent broken taps and misaligned threads.
Core principles for drilling and tapping metal
Mastering how to drill and tap a hole in metal hinges on precision, control, and preparation. This guide emphasizes measurement, secure workholding, proper lubrication, and deliberate cutting speeds. With a careful setup, you minimize wandering, broken taps, and misaligned threads. Always verify material thickness and existing features nearby to avoid collisions during drilling and tapping.
Selecting the right drill size and tap size
The thread you want is defined by its pitch and diameter; starting with the correct hole diameter is essential. For standard threads, consult the tapping chart included with your taps, or use manufacturer recommendations for the exact drill size. If you’re unsure, you can test on a sacrificial piece of scrap metal to confirm that the threads engage cleanly.
Preparing the workpiece and workholding
Clamp the workpiece securely to a flat, stable surface. Use a vise with soft jaws or a dedicated drilling jig to keep the part from shifting. For long or thin pieces, add sacrificial backing material to prevent burrs and springback that could affect hole alignment.
Marking, centering, and drill alignment
Center punches create a small dimple to guide the drill, reducing wander. Mark the intended hole precisely with a sharp marker or scribe, then verify alignment with a straight edge or calipers. If you’re using a drill press, lock the table and set a vertical alignment to ensure the drill descends perpendicular to the surface.
Drilling the pilot hole and final hole
Start with the pilot hole size, drilling straight and steady with a light feed. After the pilot hole is established, enlarge to the tapping size specified for your thread. Keep chips cleared and your drill perpendicular; switch to a slow speed as you approach final diameter.
Tapping technique and lubrication
Lubricate the tap to reduce friction and prevent galling. Begin turning slowly, applying even pressure, and back off every few turns to clear chips. Maintain perpendicular alignment and use a tap wrench or T-handle to control feed. If you feel binding, back out, re-lubricate, and realign before continuing.
Deburring, inspection, and finishing
Remove all burrs with a deburring tool or file. Clean chips from the hole and inspect the threads with a gauge or test bolt. Run a bolt through the threaded hole to verify fit and note any tight spots that require light rework. Finish by wiping the surface and removing any cutting oil.
Authoritative guidance and safety notes
In addition to following the steps above, consult authoritative safety and machining guidelines to protect personnel and equipment. OSHA safety guidelines for metalworking emphasize eye protection, proper machine guarding, and secure workholding. For learning resources, refer to university extension materials and credible safety summaries.
Tools & Materials
- Drill press or cordless drill(Set to low-to-medium speed; use a chuck that fits your bits)
- Center punch and marking tools(Create a precise indent to prevent wandering)
- Calipers or a ruler for measurement(Verify pilot and final hole sizes)
- Appropriate drill bits (pilot and final sizes)(Use high-speed steel or cobalt drill bits for metal)
- Tap drill and taps with wrench (T-handle or tap wrench)(Choose tapping size and thread count per project)
- Cutting oil or lubricant for tapping(Reduces friction and extends tap life)
- Deburring tool or small file(Remove burrs from entry and exit edges)
- Chip cleanup cloth or brush(Keeps chips clear during machining)
- Workholding with clamps or a vise(Prevents movement and ensures perpendicular drilling)
Steps
Estimated time: 60-90 minutes
- 1
Prepare and secure the workpiece
Clamp the metal piece firmly in a vise or jig. Check for flatness and ensure there is support on the underside to avoid deflection while drilling. Confirm the area around the hole is clear of obstructions and plan an exit path for chips.
Tip: Use protective jaw covers and double-check clamping tightness before starting. - 2
Mark the hole and center punch
Accurately mark the exact hole location with a sharp scribe or marker. Center punch the mark to create a small dimple, which helps the drill bite and prevents wandering.
Tip: Keep the center punch perpendicular to the surface for the best initial bite. - 3
Drill the pilot hole
Set the drill at a slow to medium speed and apply steady pressure. Drill a shallow pilot hole at the marked location, ensuring the drill remains perpendicular to the work surface.
Tip: Clear chips frequently to prevent binding and maintain accuracy. - 4
Deburr the pilot hole
Remove any burrs at the hole entrance using a deburring tool or small file. A clean entry improves tapping accuracy and reduces the risk of cross-threading.
Tip: A quick light pass is enough—don't widen the hole at this stage. - 5
Drill to the tapping size
Using the tapping chart guidance, drill the final hole with the recommended size for the desired thread. Maintain straight, perpendicular drilling through the workpiece.
Tip: If using a drill press, lock the table and verify the spindle is vertical. - 6
Lubricate and begin tapping
Apply cutting oil or light machine oil to the tap. Start turning slowly with steady pressure, keeping the tap perpendicular. Back off every few turns to clear chips and re-lubricate as needed.
Tip: Do not force the tap; fatigue and breakage increase with resistance. - 7
Finish, inspect, and deburr
Back the tap out, finish the thread path, and remove chips. Inspect thread engagement by threading a bolt; ensure smooth operation without binding. Deburr the outer edge if necessary and clean the area.
Tip: Test-fit with the intended bolt to confirm the fit before final assembly.
Got Questions?
What is the difference between drilling and tapping?
Drilling creates the hole; tapping cuts the internal threads inside that hole. The tap relies on a properly sized pilot hole to form clean threads.
Drilling makes the hole, tapping creates the threads inside it. A correctly sized pilot hole is essential for good threads.
How do I know which drill size to use for a specific tap?
Consult the tap manufacturer's chart or a reliable reference for the recommended pilot hole size for your thread. If unsure, practice on scrap metal first.
Check the chart for the exact pilot size for your tap. If in doubt, test on scrap metal.
Can I tap threads without cutting fluid?
Using cutting fluid or oil greatly reduces friction, heat, and the risk of galling. Tapping without lubrication increases wear and the chance of a broken tap.
Lubrication is essential. Without it, taps wear quickly or break.
What should I do if the tap breaks in the hole?
Back the tap out calmly and use a tap extractor if possible. If extraction fails, you may need to drill out the broken segment and re-tap at a larger size.
Back the tap out. If it won't come free, use an extractor or consider re-tapping at a larger size after removing the broken fragment.
Is a drill press required for tapping?
A drill press provides perpendicularity and consistent depth, improving thread quality. A well-clamped handheld setup can work, but it’s more challenging to maintain accuracy.
A drill press helps a lot with accuracy; a stable handheld setup can work, but accuracy is tougher.
How can I prevent wander during drilling?
Use a center punch and a sharp, appropriate drill bit. Secure the workpiece and consider using a drill press for precise, perpendicular drilling.
Center-punch the mark and clamp securely. A drill press helps keep the drill straight.
Watch Video
Top Takeaways
- Secure the workpiece to prevent drift.
- Use the correct drill and tap sizes from charts.
- Lubricate consistently to reduce wear and breakage.
- Deburr and inspect: ensure clean, accurate threads.
