Repeatedly dulling or breaking bits in metal usually means the cutting edges are overheating, rubbing instead of making chips, or being forced through work that is moving or grabbing the bit. The fix is rarely just buying another bit: match the bit to the metal, slow the drill as needed, apply steady cutting pressure, use an appropriate cutting fluid, and stop when the bit quits producing proper chips.

A sharp drill removes material as chips. A dull or poorly fed drill skates and rubs, converting more of the input into heat. Once the point overheats and loses its cutting edge, pushing harder commonly makes the problem worse. In some metals, prolonged rubbing can also harden the area around the hole, making the next attempt even more difficult.

Start With the Symptom

The bit turns blue, smokes, or becomes too hot to touch

This is a heat-control problem. Common causes include excessive speed, too little feed pressure, no suitable lubricant, or a bit that was already dull.

A drill that spins quickly but advances very slowly tends to rub at the cutting edge. Reduce speed according to the current drill-bit manufacturer’s speed-and-feed guidance for the bit diameter and material. Then use firm, controlled pressure so the bit cuts rather than polishes the surface.

Do not rely on a universal drill-speed setting. Proper speed changes with bit diameter, bit material, workpiece material, coating, setup rigidity, and the drilling method. Verify the recommended speed and feed in the current documentation from the bit manufacturer and drill manufacturer.

The bit makes shiny dust instead of chips

Fine metallic dust is a warning sign when drilling ordinary steel with a twist drill. It often means the cutting lips are rubbing rather than shearing off material. The point may be dull, the drill may be running too fast, or the operator may be easing off pressure too much.

Healthy drilling normally produces visible chips. They may be short curls, spirals, flakes, or broken pieces depending on the material and setup. Clear accumulated chips before they pack into the flutes, especially in deeper holes. Do not reach into the drilling area while the tool can run; follow the drill manufacturer’s current safety instructions before clearing chips.

The bit squeals, chatters, or skates across the metal

Squealing and skating often occur before major heat damage. The drill point may not be centered, the work may be vibrating, or the bit may be unable to bite into a hard or rounded surface.

Mark the hole location and make a starting dimple if appropriate for the workpiece and bit type. Keep the drill square to the surface. If the work moves, flexes, or vibrates, stop and improve the workholding rather than trying to overpower the bit.

For drilling equipment, clamps, vises, backing materials, and other workholding methods, use the current instructions supplied by the tool and accessory manufacturers. Verify applicable workplace or local safety guidance as well.

The bit snaps suddenly

Most broken twist drills fail because they bind, flex, or are side-loaded. A bit can bind when chips pack in the flutes, when the drill is forced at an angle, or when thin stock catches as the hole breaks through. Small bits are especially vulnerable because they have little margin for bending.

Keep the tool aligned with the hole and avoid twisting the drill sideways. Back the bit out periodically to clear chips in deeper holes, using a controlled motion rather than yanking it out under load. If drilling thin sheet, support it over a backing board or use another suitable method specified for the operation. Thin material can flex and grab at breakthrough.

Choose a Bit That Can Cut the Metal

A general-purpose high-speed steel, or HSS, twist drill is suitable for many common metal-drilling jobs when it is sharp and used correctly. It is often a practical choice for mild steel, aluminum, and other relatively machinable metals.

Cobalt HSS drill bits are designed for better heat resistance than ordinary HSS and are commonly chosen for tougher steels and heat-resistant alloys. They can be useful when the material demands a more heat-tolerant bit, but cobalt does not compensate for excessive speed, rubbing, poor chip clearing, or unstable work.

A coated bit may offer benefits in suitable applications, but coating alone does not make a bit appropriate for every metal. Match the bit material, point geometry, coating, and diameter to the workpiece using the bit manufacturer’s current application guidance.

If a bit will not start cutting despite correct setup, do not keep spinning it in place. Confirm what metal you are drilling. Hardened parts, stainless steel, unknown salvage metal, plated material, and layered assemblies can require a different bit and a different process than mild steel.

Control Speed and Pressure Together

Speed and pressure work as a pair.

  • Too much speed: Friction and heat rise quickly, which can soften or dull the cutting edge.
  • Too little pressure: The bit rubs instead of cutting, often creating heat, shine, and fine dust.
  • Too much pressure: The bit can bind, grab, flex, or break, particularly near breakthrough or in thin stock.
  • Appropriate pressure: The bit advances steadily and produces chips without forcing the tool or workpiece.

A useful rule is to respond to what the hole is telling you. If there are no chips and the surface is getting hot, stop rather than continuing to spin. Let the bit cool, inspect the cutting edges, correct the setup, and restart only if the bit is still sharp enough to cut.

Do not try to drill faster by leaning on a dull bit. A dull bit creates more heat, and heat makes dulling accelerate. Replace or properly sharpen the bit before continuing. Continuing with a damaged bit can enlarge the problem by work-hardening the surface around the unfinished hole.

Use Cutting Fluid for the Material and Operation

Cutting fluid can reduce friction and help carry heat away from the cutting zone. It is particularly useful when drilling steel and other materials that generate substantial heat.

Apply only a suitable fluid for the workpiece, bit, and setting. Some fluids are not appropriate for every metal, coating, finished surface, or indoor work area. Check the fluid label, safety data, and current guidance from the bit and workpiece manufacturers before use.

Use enough fluid to keep the cutting area lubricated, but do not let excess liquid create an unstable grip or contaminate areas where it could cause another hazard. Reapply as needed during a longer hole, and clear chips in a controlled way.

Prevent Problems With Thin Metal

Thin sheet is difficult because there is little material supporting the bit at breakthrough. The sheet may flex, the bit may pull through suddenly, or the work can catch if it is not held securely.

Clamp thin stock to a stable backing material or use a suitable fixture. A step drill may be a better choice for some sheet-metal holes because it enlarges the opening in stages, but verify that the bit is intended for the metal thickness and drill type you are using.

Avoid holding metal by hand while drilling. Follow the current instructions for your drill, vise, clamps, and any workholding accessories, and verify applicable safety requirements for the job.

Inspect a Bit Before Blaming the Metal

A bit may look usable from a distance but still be too damaged to cut well. Check for:

  • Rounded or flattened cutting lips
  • A burned or discolored point
  • Chipped edges
  • Uneven cutting lips
  • A bent shank or visibly wobbling bit
  • Packed debris in the flutes

A sharp bit has defined cutting edges and a point that starts cleanly. A rounded point tends to generate heat before it penetrates. If one cutting lip is damaged more than the other, the bit can cut an oversized hole, wander, and break more easily.

If you sharpen drill bits, maintain the correct point geometry for that bit type. If you are unsure whether a bit can be sharpened correctly, replacement is often safer and more predictable than continuing with a damaged edge.

A Quick Recovery Process When a Bit Stops Cutting

  1. Stop drilling when chip production falls off or heat rises sharply.
  2. Let the bit and workpiece cool naturally; do not handle them until they can be handled safely.
  3. Inspect the drill point for blunting, chips, discoloration, or packed debris.
  4. Confirm that the workpiece is secure and supported.
  5. Check that the bit is suitable for the metal and that the drill is set up according to current manufacturer guidance.
  6. Apply an appropriate cutting fluid if the material and operation call for it.
  7. Restart with controlled speed and enough steady feed to create chips.
  8. Stop again if the bit rubs, squeals, binds, or quits making chips.

When the Metal May Be the Main Problem

If a sharp, suitable bit immediately skates or overheats, the workpiece may be harder or less drillable than expected. Stainless steel can work-harden when rubbed. Hardened steel components may exceed the capability of ordinary HSS bits. Unknown metal can also contain hard spots, coatings, or layered materials.

Do not keep trying the same dulling setup. Identify the material if possible, then consult current bit-manufacturer guidance for the specific metal. A different bit material, point style, speed, feed, coolant approach, or machining method may be required.

The Practical Bottom Line

Drill bits dull in metal when heat wins over cutting. They break when binding, bending, or grabbing loads exceed what the bit can tolerate. The most reliable prevention is a sharp bit suited to the metal, secure workholding, controlled speed, steady cutting pressure, chip clearing, and suitable cutting fluid.

When the drill makes chips and advances steadily, continue. When it makes dust, squeals, overheats, or stalls, stop and correct the cause before the bit and the workpiece become harder to save.

References

  1. Cobalt & HSS Drills Speeds & Feeds. (n.d.). https://www.redlinetools.com/customer/docs/SKUDocs/Drill-Cobalt-HSS-Speeds-Feeds-p340.pdf
  2. Machinery’s Handbook Math for Milling Feeds and Speeds. (n.d.). https://www.reddit.com/r/Machinists/comments/1d06m4p/machinerys_handbook_math_for_milling_feeds_and
  3. CPSC. (n.d.). https://tavily.com/knowledge/company/CNFp4m03BrSV
  4. My drill bits wear super fast. Any tips? : r/Tools. (n.d.). https://www.reddit.com/r/Tools/comments/1b2zgib/my_drill_bits_wear_super_fast_any_tips
  5. Machinery’s Handbook Speeds and Feeds. (n.d.). https://www.practicalmachinist.com/forum/threads/machinerys-handbook-speeds-and-feeds.211620
  6. Feeds & Speeds For Drills | Norseman Drill & Tool. (n.d.). http://www.norsemandrill.com/feeds-speeds-drill.php
  7. How to make your drill bits last longer! - #gearznation. (n.d.). https://www.facebook.com/officialstaceydavid/videos/how-to-make-your-drill-bits-last-longer-gearznation-staceydavid-gearz-drilling-m/1217987056039823
  8. Recommended Speeds/Feeds for 7/16” HSS Drill in 3/4” …. (n.d.). https://www.reddit.com/r/CNC/comments/1k1h6c6/recommended_speedsfeeds_for_716_hss_drill_in_34
  9. Machinery’s Handbook, Pocket Companion. (n.d.). https://iem.ca/pdf/resources/Machinery's%20handbook%20pocket%20companion%20_%20a%20reference%20book%20for%20the%20mechanical%20engineer,%20designer,%20manufacturing%20engineer,%20draftsman,%20toolmaker,%20and%20machinist.pdf
  10. Metal Drilling Mistakes: How to Avoid Common Errors. (n.d.). https://www.ttp-hard-drills.net/metal-drilling-mistakes-how-to-avoid-common-errors