Drilling plastic and metal: beginner precautions

Understanding the Differences from Wood

Drilling into plastic and metal presents completely different challenges compared to drilling wood. While wood fibers generally yield and break away cleanly, plastics can melt and crack, while metals can quickly overheat and dull your drill bits.

Drilling Plastics (Acrylic, PVC, ABS)

1. The Grabbing Problem: Standard twist drill bits are designed to aggressively bite into wood or metal. When used on hard plastics like acrylic, the bit tends to grab as it breaks through the other side, which can violently pull the material and cause it to shatter.
2. Modifying the Bit (or Buying Specific Bits): For frequent plastic drilling, you can buy specific drill bits with a much steeper point angle and a flat cutting edge that scrapes rather than cuts.
3. Speed and Pressure: Drill slowly. Apply light pressure and use a low to medium RPM. If you go too fast, friction will melt the plastic, causing it to fuse around the drill bit.
4. Support the Back: Always place a scrap piece of wood behind the plastic and press it firmly against it. This provides back pressure and significantly reduces the chance of cracking as the bit exits.

Drilling Metals (Aluminium, Steel)

1. Securing the Workpiece: A drill bit catching in metal can easily spin the workpiece out of your hand, causing severe lacerations. Never hold a small piece of metal in your hand while drilling. Always secure it in a vice or use strong clamps to hold it to the workbench.
2. Creating a Starting Point: Drill bits tend to wander on smooth metal surfaces. Always use a center punch and a hammer to create a small dimple where you want the hole. The tip of the drill bit will naturally seat itself in this dimple.
3. Lubrication: Friction generates intense heat when drilling steel, which can ruin a drill bit in seconds. Use a cutting fluid (like 3-in-One oil or specialized cutting compound) to lubricate the bit, reduce heat, and prolong tool life. Aluminium is softer and can often be drilled dry or with a little WD-40.
4. Speed: For steel, use a slow RPM and firm pressure, aiming to produce continuous curly chips rather than fine dust. If it screams and sparks, you are going too fast or the bit is already dull.

Managing Burrs

When the drill bit exits metal or plastic, it often leaves a raised, jagged ring of material called a burr.

• Burrs on metal are razor-sharp and can easily slice open a finger.
• Always use a deburring tool, a countersink bit, or a small file to gently remove these sharp edges immediately after drilling.

Safety Note

Always wear safety glasses. Metal chips and shattered plastic fragments fly off at high speeds. Wear ear protection when drilling metal, as it can be surprisingly loud.