Files
- 2D drawing
- 3D CAD / STEP file
- Drawing revision if applicable
Engineering-oriented CNC machining support
CNC Machining Tolerances for Custom Parts
Review critical dimensions, functional fits, geometric tolerances, datum references, and inspection expectations before quotation, especially when drawings include tight or unclear tolerance requirements.
Critical dimensions and fitsFlatness, runout and hole positionDrawing tolerance reviewInspection method discussion
Tolerance service scope
Tolerance Review Scope
Tolerance requirements affect manufacturability, machining time, inspection effort, cost, lead time, and quotation accuracy. KENDORIC helps buyers review drawings, CAD files, material choices, machining methods, finishing requirements, datum references, and inspection expectations before quotation. The goal is to identify which dimensions are function-critical and which can follow practical general tolerances.
Critical Dimensions
Fits, bearing seats, sealing faces, datum surfaces, alignment features, and assembly-critical dimensions.
Geometric Tolerances
Flatness, parallelism, perpendicularity, concentricity, runout, hole position, and datum relationships.
Cost and Feasibility Review
Identify where tight tolerances are necessary and where standard machining tolerances may be sufficient.
Inspection Expectations
Clarify whether calipers, micrometers, gauges, bore gauges, CMM-style inspection, or reports are required.
Drawing preparation
How to Specify Tolerances on Drawings
General vs Critical Tolerances
Use general tolerances for ordinary dimensions and specific callouts for functional features.
Datum References
Define datum surfaces and measurement orientation when geometric tolerances or multi-setup features matter.
Functional Fits
Mark bores, shafts, bearing seats, sealing faces, threads, and mating dimensions clearly.
Inspection Notes
State which dimensions need recorded inspection results instead of requiring reports for every feature.
RFQ checklist
CNC Tolerance Review Checklist for RFQ
| Review Item | Why It Matters | Buyer Action |
|---|---|---|
| Critical dimensions | Focuses machining and inspection on functional features | Mark dimensions that affect fit, alignment, sealing, or movement |
| Datum references | Controls how features are measured and related | Confirm datum surfaces and assembly orientation |
| Bore and shaft fits | Small changes can affect assembly performance | Provide mating part information or fit expectation if available |
| Flatness and parallelism | Important for mounting, sealing, and fixture parts | Identify functional faces and acceptable variation |
| Hole position | Affects assembly with bolts, pins, and mating plates | Mark critical hole patterns and related datums |
| Surface finish | Can affect sliding, sealing, appearance, or coating | Specify only where function or appearance requires it |
| Post-finishing dimensions | Coatings or heat treatment can change final dimensions | State whether dimensions apply before or after finishing |
| Inspection requirements | Determines measuring method and report scope | Identify features that require recorded inspection results |
Manufacturing impact
Tight Tolerances, Cost and Manufacturing Risk
Machining Time and Setup
Tight tolerances may require slower machining, better fixturing, extra setup control, or process changes.
Inspection Effort
Critical features may need micrometers, bore gauges, thread gauges, height gauges, or CMM-style inspection.
Design Risk
Thin walls, deep pockets, long shafts, small bores, coated surfaces, or heat-treated features may need early feasibility review.
Part behavior
Material, Geometry and Process Factors
Aluminum Parts
Thin walls, deep pockets, large flat faces, and heavy material removal may affect stability.
Stainless Steel Parts
Tool wear, heat control, surface finish, tight bores, and critical diameters may need closer review.
Turned Parts
Runout, concentricity, OD/ID fits, shoulders, grooves, and bearing surfaces can drive inspection needs.
Milled Parts
Flatness, hole position, datum faces, pockets, slots, and multi-setup features should be reviewed.
Measurement planning
Inspection Methods and Reports
Basic Measurement
Calipers, micrometers, height gauges, bore gauges, plug gauges, and thread gauges may be suitable for many features.
CMM-style Inspection
Useful when geometry, datum relationships, hole positions, profiles, or multi-feature relationships require closer review.
Focused Reports
Inspection reports should focus on critical dimensions instead of recording every non-critical feature when not necessary.
Quotation inputs
RFQ Information Needed for Tolerance Review
Tolerance Details
- Critical dimensions
- Datum references
- Fit requirements
- GD&T / geometric tolerances
- Surface finish notes
Inspection Needs
- Inspection report required or not
- Dimensions to record
- Mating part information
- Post-finish dimension concerns
Send Drawings for Tolerance Review
Share your 2D drawings, 3D CAD files, material, quantity, critical dimensions, tolerance notes, surface finish, inspection requirements, and delivery details for review before quotation.
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