从机制开始
A useful gear tolerance plan focuses on the characteristics that control the mesh and mounting relationship.
Bore-to-tooth runout, tooth-to-tooth variation, overall geometry and the center distance in the assembly all influence working performance. Molding adds material shrinkage and process variation that should be reflected in datum and inspection choices.
Consider an assembly where the bore locates on a steel shaft and the mate is fixed in a molded housing. A tight outside-diameter tolerance on the gear does little if bore runout or housing center distance dominates the mesh. The drawing should therefore distinguish tooth geometry from mounting geometry and place the inspection datum on the feature that actually locates the gear in service.
报价前需冻结的输入数据
Define the gear standard/convention, module or DP, pressure angle, bore datum, mating gear, center distance, backlash target and measurement condition.
尽可能将这些信息添加到受控图纸、规格说明或询价附件中。避免在非正式的沟通渠道中发布这些信息，有助于供应商比较和后续修改的管理。
什么因素会使这一假设失效？
Overtightening every drawing dimension can increase tooling and inspection cost without controlling the actual mesh.
验证策略
Combine dimensional gear checks with an assembled roll or functional test when that better represents the mechanism.
For Injection Molded Gear Tolerances, close the DFM loop by updating the controlled CAD/drawing and sample plan. A recommendation that never reaches the released revision cannot be inspected consistently in production.
采购清单
Before requesting a price for injection molded gear tolerances, identify the current drawing revision, production quantity, material constraint and the feature that most strongly affects function. Ask the supplier to flag any deviation from those inputs in the quotation so technical alternatives stay visible.
针对此决策的实用设计审查
Tolerance should be allocated from the assembly backward. Start with required working backlash or position, then include center-distance variation, tooth-to-bore runout, shaft/bearing clearance, material movement and measurement uncertainty. Tightening every free-part dimension can increase cost without protecting the assembled condition.
将假设条件记录在图纸或询价单中，以便供应商在报价前进行确认。如果某个数值未知，应将其标识为待定工程项目，而不是直接复制可能与实际装配不符的通用产品目录编号。
验证工作表
- Working rather than nominal clearance
- Bore-to-tooth or rack-to-mount datum relationship
- Mating-part tolerance
- Inspection temperature / conditioning
- Functional roll, mesh or position check
- Acceptance method agreed before sampling
使用第一个样品，通过尺寸验证和相关的功能检查来确认这些要点。任何可接受的偏差都应在重复生产前的受控修订中记录下来。
