I use 2020 aluminum extrusions for various pieces of shop furniture. This document is the process I use to tap the ends for corner blocks or blind joints. ## Tools and Materials For this process, I use a straightforward setup: - [M6 Combination Tap](https://www.amazon.com/dp/B0B1VBVVH6) - [Cutting Fluid](https://www.amazon.com/dp/B00065VEP4) - [Countersink](https://www.amazon.com/dp/B08VHYBC8K) - Drill - Clamps (to secure extrusion to MFT/3) - Compressed air ## Preparation Start by clamping the extrusion securely to a flat work surface. I typically use the MFT/3 since it has a grid of dog holes that make clamping easy. If the extrusion shifts while tapping, the threads can become misaligned or damaged. It’s also worth confirming that the extrusion ends are cut square. Factory edges should be fine, but it is worth verifying. ## Tapping Process 1. Insert the M6 combination tap into the drill. 2. Apply cutting fluid to the tap. I generally keep a small disposable cup of cutting fluid available. 3. Run the drill slowly into the extrusion end. 4. Back the tap out periodically to break chips and reduce the risk of binding. 5. Once the hole is complete, blow out chips with compressed air. 6. Brush away stubborn chips with a brass brush. ## Finishing Once the tap is complete, use a countersink to clean up the opening. Chamfering ensures the edge remains square and makes it easier to start fasteners into the new threads. Test-fit an M6 screw to provide smooth engagement and proper depth. ## Tips and Considerations - Don’t rush the tapping process. Clearing chips frequently is better than forcing the tool. - Use screws that extend into the extrusion by at least 8–10 mm. ## Lessons Learned On one occasion, I forgot to apply cutting fluid before tapping. The aluminum quickly bound up around the tap, and the bit snapped under pressure. It was a good reminder that lubrication isn’t optional, especially in aluminum, which tends to clog cutting edges. Now I make a point to stop before every pass and reapply fluid if needed. It slows the process slightly but saves tools and prevents broken taps from getting stuck in the extrusion. ![[Discussions]]