Don’t mess with chamfering threaded holes; doing it wrong will cause jamming and damage to parts.

Who hasn’t casually marked “1×45°” for chamfered threaded holes on their drawings? Machining technicians have probably done it too!

But you might not know that this seemingly “harmless” little mark can easily lead to assembly jams, thread scratches, and loose connections—especially for designers who haven’t handled actual machining, who are most prone to making these mistakes!

 

Why can’t chamfering be done “at will”?

Many people think “any chamfer will do,” but they overlook the core problem: burrs.

If the chamfer is too small (e.g., 1×45° for an M8 thread), the sharp edges of the threaded opening cannot be removed during machining, easily leaving burrs:

• During assembly, burrs can obstruct the bolt, causing alignment difficulties and jamming;

• Forcing it in can cause burrs to scratch the internal threads, resulting in misalignment and seizing;

• Even if it’s installed, burrs can lift the fitting, leading to a loose fit and connection.

Looking at the nut standard explains it: The national standard for nut chamfering is 90°~120°, and the diameter must be larger than the nominal thread diameter—the core reason is to completely avoid burrs and ensure a sufficient contact area.

Golden Rules for Chamfering (Direct Application)

No complicated calculations needed. Remember these two core principles to avoid common pitfalls:

1. Prioritize 45° angle: Suitable for most scenarios, simple processing, and good guidance;

2. Dimensions are critical: Exceed the major diameter of the thread: Ensures coverage of the sharp edge of the thread, preventing burrs at the source.

Common Specifications Quick Reference Table (Directly copy into drawings)

Thread specifications	Recommended chamfer	Core Requirements
M3-M6	0.5~1×45°	Diameter > Major diameter of thread
M8-M12	1~1.5×45°	The countersunk parts need to be fitted to the step.
M14-M20	1.5~2×45°	Hard materials +0.2~0.3mm

Tip: When unsure of the dimensions, simply use the “thread pitch P” as the chamfer dimension! For example, marking an M8 (1.25mm pitch) as 1.25×45° is absolutely reliable.

⚠️ Special Scenarios to Avoid Pitfalls

• Thin-walled parts / shallow threaded holes: Chamfer depth ≤ 1/3 of the effective thread depth; avoid weakening strength.

• Tapered fits / special assemblies: A 60° chamfer can be used, but avoid <30° or >90°.

Although the chamfer of a threaded hole is small, it directly affects machining efficiency, assembly smoothness, and product lifespan. Those casually marked “1×45°” often reveal a lack of understanding of machining logic.