Identify what is truly critical
A machining drawing may contain dozens or even hundreds of dimensions. However, not every dimension has the same effect on part function. The supplier needs to understand which features affect assembly, motion, sealing, positioning or service life. Applying tight tolerances to every dimension can increase machining and inspection costs without improving the part's function.
Define the assembly datums first
Features used for positioning or assembly often become the starting point for machining and inspection planning. Clear datums help the supplier determine the machining sequence and establish a consistent measurement reference.
- Locating and centre holes
- Bearing seats
- Flange faces
- Mating diameters
- Assembly contact surfaces
Mark the critical dimensions
Critical dimensions directly affect how the part functions or assembles. Drawing symbols, numbered characteristics or a separate inspection list help the supplier consider fixturing, tooling, machining sequence and measurement strategy at an early stage.
- Shaft and bore fits
- Hole-to-hole relationships
- Perpendicularity between a face and an axis
- Concentricity between internal and external diameters
- Wall thickness on thin-wall components
- Flatness of assembly surfaces
Match tolerances to function
A tighter tolerance usually requires more process control and inspection time. Standard tolerances may be suitable for non-critical dimensions, while tighter dimensional or geometric tolerances should be reserved for features that affect assembly or operation.
Confirm inspection and documentation during quotation
Inspection requirements affect fixturing, measurement time, documentation and quotation cost. When only selected dimensions require recorded results, a full report for every drawing dimension may not be necessary.
- First article inspection
- Critical-dimension reports
- Full or sampling inspection
- CMM inspection
- Keyence vision measurement
- Material and finishing certificates
Choosing between CMM and vision measurement
CMM inspection is commonly used for complex geometry, datum relationships, hole positions, flatness, perpendicularity, concentricity and position. Keyence vision measurement is often suitable for profiles, small holes, slot widths, two-dimensional relationships and small features that are difficult to measure by contact. The method should suit the feature rather than being selected by equipment name alone.
Do not treat on-machine probing as final acceptance by default
On-machine probing can support workpiece set-up, alignment and in-process checks, but results still depend on machine condition, probe setup and the production environment. If the part requires a formal acceptance record, the RFQ should separately define the final inspection method, sampling quantity, report format and decision criteria.
Run a measurement-risk check before sending the RFQ
Confirm the drawing revision, datums, tolerances, critical features, material condition, dimensions before and after finishing, and whether each feature can be reached or viewed by the intended instrument. Flag features that may be coated, distorted or difficult to locate repeatably so the acceptance method can be agreed before machining.
An unfinished drawing can still be reviewed
Prototype drawings often change during development. The current revision can be submitted while open items are clearly marked for discussion. The supplier can review the available information first, then identify items that may affect cost, quality or manufacturability.
- Current drawing revision
- 2D PDF and available 3D model
- Estimated quantity and target delivery
- Material and finish
- Critical dimensions
- Functional or assembly requirements
How Jintat supports the review
Jintat Industrial provides CNC turning, milling, mill-turn machining and precision inspection support for prototypes, high-mix low-volume work and small-batch production.