Designing for Tapped Holes in Die-Cast Parts: What You Need to Know

Tapped holes are commonly required in die-cast parts for assembly—whether for screws, studs, or helicoils. But without careful planning, they can lead to cracks, broken taps, or misaligned fasteners.

Whether you're using aluminium (e.g. ADC12) or zinc (e.g. Zamak 3), proper DFM (Design for Manufacturability) is essential when planning tapped holes.

🔧 Best Practices for Tapped Hole Design:

1. Avoid Threading in As-Cast Features

   Cast threads are unreliable. Always tap holes after casting, either via CNC or manual tapping.

2. Maintain Minimum Wall Thickness

   For metric threads, maintain at least 2x the thread diameter around the hole to prevent cracking.

3. Use Draft Where Possible (Pre-Machined Holes)

   Core pins used to form the pilot hole should include proper draft to allow ejection—typically ~1–2°.

4. Consider Boss Design

   Raised bosses are preferred for threaded holes. This avoids thin-wall tapping and allows ejector pin support beneath the hole.

5. Use Thread Inserts (e.g. Helicoils) for Soft Alloys

   Especially in ADC12, helicoils or press-fit inserts help ensure thread durability over repeated use.

6. Control Depth and Blind Hole Debris

   Chips from tapping must be cleared if used in blind holes. Avoid bottoming out during assembly.

At LVIO Precision, we use programmed CNC tapping cycles for precision—and where required, advise customers early on hole location, thread pitch, and tolerance stack-up to ensure fastener success and part integrity.