THREAD DESIGN / CNC MACHINING INSIGHTS
Tapped holes are common on brackets, housings, covers and machined assemblies. The machining itself may be routine, but the drawing needs to answer a few practical questions: what thread, how much usable engagement, where the tool enters, and whether any finish changes the final fit.
Use a complete tapped-hole callout
State the thread standard and complete designation next to the feature. For a multi-hole pattern, use a schedule or quantity note that makes it clear which locations share the same requirement. The ASME B1.1 reference is a useful primary source for Unified inch-thread terminology.
Separate usable thread depth from drilled depth
For a blind tapped hole, the full-depth engagement needed by the mating screw is usually more important than the total drilled hole depth. Write the requirement so the manufacturing team can distinguish the usable thread length from the bottom condition. If a screw must bottom out, seal, or stop at a controlled location, include that functional context.
| Drawing item | Why it matters |
|---|---|
| Thread designation | Defines the required standard, size, pitch or threads per inch, and class if needed. |
| Hole condition | Clarifies blind versus through and the tool approach. |
| Usable thread depth | Defines the engagement requirement for a blind threaded feature. |
| Lead-in feature | Shows any functional countersink, chamfer or spotface around the opening. |
| Finish requirement | Lets the process review consider coating or post-machining sequencing. |
Dimension lead-ins when they serve a function
A chamfer or countersink may guide a fastener, remove a sharp edge, seat a head, or protect a mating feature. If it is functional, dimension it directly. If it is a general non-critical edge treatment, use a clear deburr note instead. Our edge-break guide explains how to separate those two requirements.
Plan threads with finishing
Include anodizing, heat treatment or other final finishing in the RFQ before the machining sequence is reviewed. Finishing may affect mating conditions on threads or adjacent contact faces. The drawing or RFQ should identify whether a feature needs masking, protection, or a final operation after finishing.
Use a pattern schedule for complex parts
Housings and brackets may contain multiple thread sizes, orientations and depths. Number the feature groups, then list the thread callout, quantity and special requirement in a small table. This makes the RFQ easier to check against both the 3D model and the released PDF drawing.
State the inspection expectation for critical threads
If a thread is critical to the assembly, identify what must be verified and link it to the drawing feature. ExactMach coordinates drawing-defined CNC milling, CNC turning, prototypes and custom parts around Shenzhen and Dongguan, including anodizing and heat-treatment support where required.