Release time：2020-01-16 18:44 Browse：
The tip of a self-drilling screw acts like a miniature drill bit. If this "bit" fails, the screw cannot advance.
Material Hardness Mismatch (Most Common Cause)
Problem: The hardness of the screw's drill tip is much lower than the hardness of the material being fastened. For example, using a standard low-carbon steel screw on high-strength steel or thick metal will cause the tip to skid without biting in.
Analogy: It's like trying to drill into a steel plate with an iron nail – it will inevitably fail.
Poor Tip Design or Wear
Problem: The geometry (cutting edges) of the drill tip is poor or has become worn or chipped. A sharp, correctly angled tip is essential for efficient cutting. If it's poorly manufactured from the start or was damaged during a previous attempt, it loses its cutting ability.
Symptom: The screw spins in place, making a high-pitched grinding noise, but doesn't advance. It may even polish a smooth dimple on the surface.
Incorrect Speed and Pressure
Problem: Insufficient pressure is the primary reason. The operator does not apply enough axial thrust (forward-pushing force) with the drill. Self-drilling screws need constant pressure to "bite" into the material and start cutting. Without enough pressure, they just friction-spin.
Speed Too Low: RPM that is too slow leads to inefficient cutting, feeling like it "won't go." However, a more common issue is excessively high speed, especially when used with an impact driver. High RPM without adequate pressure causes the tip to overheat instantly, annealing and destroying it.
Material Too Thick or Wrong Screw Selected
Problem: The drill tip length of a screw is limited; it can only effectively penetrate a certain material thickness. For example, using a screw rated for 5mm steel on a 10mm plate will cause it to stall once the tip has fully penetrated, as the following shank has no cutting ability.
Symptom: The screw drills partway in and then suddenly stops.
Breaking usually occurs after the screw has partially drilled in and is the result of a combination of stresses.
Excessive Torque (The Core Reason)
Pilot Hole Too Small or Threads Too Tight: The screw shank diameter doesn't match the pilot hole (if used), or the threads are engaging too tightly with the material, creating huge friction.
Hard Spots in the Material: Impurities in steel, hard knots in wood, or aggregate in concrete can cause a sudden spike in resistance.
Using a Worn-Out Tip: A dull tip creates massive drilling resistance, transferring immense torque to the shank, leading to breakage.
Incorrect Power Tool Settings: Using the hammer action (hammer drill mode) on an impact driver or drill is a major cause. The percussive blows easily snap screws. Always use the drill/drive setting only. NEVER use the hammer setting.
Problem: The resistance (torque) encountered while drilling or driving the screw exceeds the ultimate tensile strength of the screw's shank, causing it to twist off at its weakest point (usually where the threads start).
Specific causes of high torque:
Poor Screw Quality or Heat Treatment
Problem: The screw itself is of inferior quality. To reduce costs, manufacturers use poor-quality steel or improper heat treatment, making the screw too brittle (lacking toughness). A quality self-drilling screw needs a balance: a hard tip and a tough shank. A poor-quality screw has a brittle shank that snaps easily under uneven stress.
Improper Operation: Off-Angle Driving
Problem: The drill is not held perpendicular to the work surface, causing the screw to go in at an angle. This subjects the screw to significant bending stress and causes one side of the threads to be over-compressed, drastically increasing resistance until it snaps from being "bound up."
Analogy: It's like breaking a wire by bending it back and forth.
Mismatch Between Screw and Pilot Hole
Problem: On very hard materials, a pilot hole is sometimes necessary. If this pilot hole is drilled too small, the screw encounters enormous resistance when forming the threads, leading to breakage.
To ensure self-drilling screws work correctly, follow these guidelines:
| Problem Type | Primary Cause | Prevention & Solution |
|---|---|---|
| Failure to Drill | 1. Insufficient Pressure | Apply steady, firm axial pressure to ensure the tip bites into the material. |
| 2. Material Mismatch | Select the correct type: Choose a screw grade suitable for the material's hardness (e.g., different screws for steel, stainless steel, aluminum). | |
| 3. Worn/Poor Quality Tip | Use quality brand-name screws; inspect the tip for sharpness; avoid reusing worn screws. | |
| 4. Material Too Thick | Select a screw with a drill tip length greater than the total material thickness. | |
| Breaking | 1. Excessive Torque | Adjust the power tool: Use the screwdriver/drill setting and set an appropriate torque level. ABSOLUTELY AVOID HAMMER MODE! |
| 2. Off-Angle Driving | Keep the drill perpendicular to the work surface. Apply force smoothly and evenly. | |
| 3. Poor Screw Quality | Purchase reputable brand screws to ensure the shank has sufficient toughness. | |
| 4. Incorrect Pilot Hole | Drill a pilot hole of the appropriate size if needed for hard materials. |
In short, remember three key points:
Choose the right screw (check material and specifications).
Use the right tool settings (no hammer mode, correct torque).
Apply the right force (perpendicular, firm pressure, steady speed)
