Left-hand drill bits are primarily used for removing broken screws, bolts, or fasteners. They are designed to rotate counterclockwise, which is the opposite direction of standard right-hand drill bits. This counterclockwise rotation is beneficial because it can help loosen and extract fasteners that are stuck or have broken off within a material. When a left-hand drill bit is used, the drilling action itself can sometimes grip the broken fastener and unscrew it from the material, eliminating the need for additional extraction tools. These drill bits are particularly useful in situations where a fastener has been over-tightened or has rusted in place, making it difficult to remove with conventional methods. By drilling into the center of the broken fastener, the left-hand drill bit can create a pilot hole that can either directly remove the fastener or prepare it for further extraction using a screw extractor. Additionally, left-hand drill bits are often used in conjunction with screw extractors. The pilot hole created by the left-hand drill bit provides a starting point for the extractor, which can then be used to remove the fastener without damaging the surrounding material. In summary, left-hand drill bits are specialized tools used for extracting broken or seized fasteners by drilling in a counterclockwise direction, which can help loosen and remove the fastener from the material.

1. **Select the Right Drill Bit**: Choose a left-hand drill bit slightly smaller than the diameter of the broken screw. 2. **Secure the Workpiece**: Ensure the object containing the broken screw is stable and secure to prevent movement during drilling. 3. **Center Punch the Screw**: Use a center punch to make a small indentation in the center of the broken screw. This helps guide the drill bit and prevents it from slipping. 4. **Set Up the Drill**: Insert the left-hand drill bit into a reversible drill. Set the drill to rotate counterclockwise (reverse setting). 5. **Drill into the Screw**: Position the drill bit in the center punch mark. Begin drilling slowly, applying steady pressure. The left-hand drill bit will bite into the screw and may start to unscrew it as it drills. 6. **Monitor Progress**: As you drill, the bit may catch and begin to turn the screw out of the hole. If this happens, continue drilling until the screw is fully removed. 7. **Use an Extractor if Needed**: If the screw does not come out with the drill bit alone, stop drilling and insert a screw extractor into the hole. Turn the extractor counterclockwise to remove the screw. 8. **Clean the Area**: Once the screw is removed, clean the hole of any debris or metal shavings. 9. **Inspect and Repair**: Check the hole for damage. If necessary, repair or re-tap the threads before inserting a new screw.

High-speed steel (HSS) and cobalt drill bits are both used for drilling, but they differ in composition, performance, and applications. 1. **Composition**: - **HSS Drill Bits**: Made from a combination of steel with elements like carbon, vanadium, and chromium. They are designed to withstand high temperatures and maintain hardness. - **Cobalt Drill Bits**: A type of HSS drill bit with an added 5-8% cobalt content. This addition enhances their heat resistance and durability. 2. **Heat Resistance**: - **HSS Drill Bits**: Can handle moderate heat levels, suitable for general-purpose drilling in materials like wood, plastic, and soft metals. - **Cobalt Drill Bits**: Superior heat resistance, making them ideal for high-speed drilling and tougher materials like stainless steel and cast iron. 3. **Durability**: - **HSS Drill Bits**: Less durable than cobalt bits when used on hard materials. They may wear out faster under high-stress conditions. - **Cobalt Drill Bits**: More durable and maintain their cutting edge longer, even under high temperatures and stress. 4. **Cost**: - **HSS Drill Bits**: Generally less expensive, making them a cost-effective choice for everyday drilling tasks. - **Cobalt Drill Bits**: More expensive due to their enhanced performance and longevity, but cost-effective for heavy-duty applications. 5. **Applications**: - **HSS Drill Bits**: Suitable for general-purpose drilling in softer materials. - **Cobalt Drill Bits**: Preferred for drilling hard metals and applications requiring high precision and durability. In summary, cobalt drill bits offer enhanced performance for demanding tasks, while HSS drill bits are suitable for general use. The choice depends on the material being drilled and the specific requirements of the task.

Non-coolant-through drill bits require a separate hose for coolant because they lack internal channels to deliver coolant directly to the cutting edge. Coolant is essential in drilling operations to reduce heat, minimize tool wear, and improve surface finish. Without internal channels, an external method is necessary to supply coolant to the drill bit. A separate hose allows for the precise delivery of coolant to the drill bit's cutting area. This external system ensures that the coolant reaches the point of contact between the drill bit and the workpiece, effectively reducing friction and dissipating heat. The hose can be adjusted to direct the coolant flow exactly where it is needed, enhancing the cooling and lubrication process. Additionally, using a separate hose for coolant provides flexibility in controlling the flow rate and pressure of the coolant, which can be adjusted based on the material being drilled and the specific requirements of the operation. This adaptability is crucial for optimizing drilling performance and extending the life of the drill bit. In summary, non-coolant-through drill bits require a separate hose for coolant to ensure effective cooling and lubrication, as they lack internal channels for direct coolant delivery. This setup allows for precise control over coolant application, improving drilling efficiency and tool longevity.

Jobber-length drill bits are standard drill bits characterized by their length, which is typically 9 to 14 times the diameter of the drill bit. This length provides a good balance between reach and rigidity, making them versatile for a wide range of drilling applications. They are longer than stub-length bits but shorter than extra-length bits, offering a middle ground that suits many general-purpose drilling tasks. These drill bits are commonly used in metalworking, woodworking, and plastic drilling. Their design allows for effective chip removal and heat dissipation, which is crucial for maintaining the integrity of the material being drilled and the longevity of the drill bit itself. The length of jobber bits makes them suitable for drilling deeper holes than stub-length bits, while still maintaining sufficient rigidity to prevent bending or breaking. Jobber-length drill bits are ideal for use in handheld drills and drill presses, providing the flexibility needed for various projects. They are particularly useful when working with materials of moderate thickness, where a balance between depth and control is necessary. Additionally, they are available in a wide range of sizes and materials, such as high-speed steel, cobalt, and carbide, allowing them to be tailored to specific materials and applications. In summary, jobber-length drill bits should be used when you need a versatile, general-purpose drill bit that offers a good compromise between reach and stability. They are suitable for a variety of materials and are a staple in both professional and DIY toolkits.