Six areas on customer drawings are where problems most frequently arise.
Having handled custom manufacturing based on customer drawings for years, I have seen a wide variety of prints. Looking back, most communication overhead and rework stem not from a lack of manufacturing capability, but from missing information or contradictory specifications on the drawings. Getting the following details right leads to faster quoting and smoother mass production.
1. Specifying only “Stainless Steel”
There are significant differences in price and machinability between grades like 201, 304, and 316. Grade 201 is inexpensive but offers only average corrosion resistance and poor formability; 304 is the standard, all-purpose choice; 316 contains molybdenum, offering resistance to chloride-ion corrosion—making it suitable for coastal or chemical environments—but it comes at a much higher price. The same logic applies to cold-rolled steel sheets: SPCC, SECC (electro-galvanized), SGCC (hot-dip galvanized), and DC04 (deep-drawing grade) cannot be used interchangeably. For instance, using standard SPCC for deep-drawn parts significantly increases the risk of cracking.
One more point: do not omit the material standard and temper/condition. Specifying “SUS304 1/2H” indicates a half-hard temper, which differs vastly from the soft (annealed) state in terms of formability and hardness; similarly, 5052-H32 and 1060-O aluminum sheets are entirely different materials. This information is crucial for determining whether the part can actually be manufactured.
2. Providing only 3D models without 2D tolerances
3D models do not inherently contain tolerance data, leaving manufacturers unable to determine which dimensions require strict control. It is essential to clearly distinguish between critical dimensions (CTQ) and those subject to general tolerances. We recommend applying specific tolerances only to dimensions critical for assembly, while applying general tolerances—such as GB/T 1804-m or ISO 2768-m—to the rest.
Marking dozens of dimensions with a ±0.05 tolerance exponentially increases manufacturing costs, and many of these tight tolerances are often unnecessary. Conversely, failing to specify tolerances for critical dimensions can lead to even greater losses: parts might be produced within tolerance limits yet fail to assemble correctly. III. Missing Geometric Tolerances
Form and positional tolerances—such as flatness, perpendicularity, coaxiality, and position—often have a greater impact on assembly than dimensional tolerances. For instance, a large panel might have a length tolerance of ±0.2 (which seems generous), but without a specified flatness tolerance, a 2 mm warp after welding wouldn’t technically be “out of spec”—yet it would result in a visible gap when mounted on the cabinet.
For groups of holes that mate with other parts, it is best to specify position tolerance directly and clearly define the datum system (primary, secondary, and tertiary datums). Inconsistent datums lead to errors accumulating across different machining stages, resulting in incorrect hole spacing during final assembly.
IV. Vague Surface Treatment Requirements
Simply stating “zinc plating” is insufficient. You must specify the process (e.g., blue-white zinc, colored zinc, nickel plating, anodizing), coating thickness, color, salt spray test duration and acceptance criteria, masking areas, and whether threaded holes should be plated. If applicable, include the relevant standard numbers (e.g., GB/T 9799 or ISO 2081).
V. Imprecise Welding and Deburring Requirements
Welding symbols should follow GB/T 324 or ISO 2553, specifying the weld type (fillet, plug, butt), leg size, whether full welding is required, and the extent of post-weld grinding. Without these details, quotes must be based on conservative estimates, which is disadvantageous for both parties.
The same applies to deburring. “Remove burrs” is too vague; specifying details—such as whether to use a C0.5 chamfer or R0.3 radius, and whether to treat all edges or only exposed ones—ensures accurate quoting and prevents disputes during production.
VI. A Few Extra Notes Beyond the Drawings
It is also helpful to provide information on annual usage, the part’s installation location, why the previous supplier stopped making it, and whether any past failures occurred. This information isn’t explicitly stated on the drawings, yet it significantly influences the choice of manufacturing process—for instance, the construction methods for a load-bearing bracket differ entirely from those for a decorative one.
Our engineers conduct drawing reviews to compile a comprehensive list of the aforementioned issues and all opportunities to optimize manufacturability. Modifying drawings before the design is finalized comes at no extra cost, whereas changes made after mold fabrication involve a completely different set of expenses.
