Quick answer: For machined aluminum parts, alloy and temper alone are not enough. Buyers should define the bar diameter, diameter tolerance, straightness over a stated gauge length, surface condition, cut length, inspection method and the amount of machining stock. These requirements determine whether a bar can run reliably through a lathe, bar feeder or machining center.
A bar may meet its material specification yet still create production problems if its straightness, surface damage or dimensional variation is unsuitable for the downstream process. This guide explains how to prepare a technically complete RFQ without applying an unnecessarily tight tolerance to every order.
Why Straightness and Diameter Control Matter
Bar Feeding and High-Speed Rotation
Long round bar that is not sufficiently straight can vibrate during rotation, load unevenly in a guide channel or create unstable contact in a bar feeder. The practical limit depends on bar diameter, unsupported length, rotational speed, machine configuration and the finished-part requirement. A straightness value should therefore always include the length over which it is measured.
Diameter, Chucking and Machining Allowance
Diameter tolerance affects chucking consistency, collet selection and available machining stock. If a drawing specifies only the finished diameter, the supplier cannot determine the correct starting size. The RFQ should separate the supplied-bar diameter from the finished-part dimension and state whether peeling, turning, grinding or polishing is required.
Surface Condition and Defect Removal
Extruded, cold-finished, peeled and ground bars have different surface characteristics and dimensional capability. A bright appearance does not by itself establish dimensional accuracy or defect-removal depth. For critical parts, specify allowable surface marks, decarburization concerns where relevant, protective packing and whether the supplied surface remains on the finished component.
Information to Put on the Drawing or RFQ
| Item | What to State | Why It Matters |
| Alloy and temper | Complete designation and governing material standard | Controls chemistry, condition and acceptance basis |
| Supplied diameter | Nominal diameter and permitted variation | Sets machining stock and tooling range |
| Straightness | Maximum deviation over a defined gauge length | Avoids an ambiguous whole-length requirement |
| Length | Random, fixed or cut length and length tolerance | Affects handling, nesting and end loss |
| Surface | Extruded, cold-finished, peeled, ground or polished | Defines appearance, dimensional capability and stock removal |
| Inspection | Measurement method, sampling level and required report | Aligns supplier and buyer acceptance decisions |
Choose the Product Condition for the Process
General Machining Blanks
For conventional machining where the entire surface will be removed, a standard commercial bar condition may be sufficient. Allow enough stock for cleanup and confirm that the selected alloy and temper provide the required strength, machinability, corrosion performance and response to finishing.
Automatic Lathes and Bar Feeders
Continuous feeding can make straightness, diameter consistency, end preparation and bar length more important. Share the feeder type, guide-channel range and intended rotational condition. Do not copy a tolerance from an unrelated diameter or machine without confirming that it can be measured and supplied consistently.
Precision Shafts and Visible Surfaces
If part of the supplied surface remains on the finished component, define roughness, appearance, local defects and protective handling separately from diameter tolerance. Ground bar may be appropriate when tighter geometry and a controlled finish are necessary, but the required condition should follow the finished-part function rather than appearance alone.
Inspection and Acceptance
Diameter should be checked with calibrated equipment at agreed positions and orientations. Straightness may be assessed on a suitable reference surface or by another agreed method, but the support condition, measurement span and reporting resolution must be consistent. For long or slender bars, handling and temperature can influence the result.
A material certificate confirms the ordered alloy and temper according to the applicable documentation scope; it does not automatically certify every dimensional or surface requirement. Request a dimensional report, traceability, mechanical testing or other inspection only when it is relevant to the part risk and purchase specification.
Practical RFQ Checklist
- Alloy, temper and governing standard
- Supplied diameter, tolerance and required machining allowance
- Straightness limit and stated measurement length
- Random or fixed length, cut tolerance and end condition
- Required surface condition and allowable marks
- Quantity, packing method and destination country
- Certificate, traceability and inspection-report requirements
- Finished component, machining route and critical acceptance features
Available product forms and inquiry options can be reviewed in the aluminum bar range. Sharing the drawing and machining route helps align the supplied condition with the actual production need.
Post time: Sep-08-2026