What drives the cost of a turned part

1. 01Material: the alloy price (brass follows the copper market) and the bar size. The part is machined from the smallest standard bar that covers its largest diameter, so a single oversized collar can raise the cost of the whole part.
2. 02Cycle time: how long each part spends on the machine. More features, deeper holes and slow materials take longer.
3. 03Secondary operations: cross holes, flats, slots and knurls that cannot be finished in the main turning cycle need another set-up and handling.
4. 04Tolerances and inspection: every tighter tolerance means slower cutting, more checking and more parts rejected.
5. 05Quantity and set-up: set-up time is shared across the batch, so small batches carry more set-up cost per part. Very high volumes can justify dedicated tooling that makes each part cheaper.

The single most effective way to reduce cost is to keep tight tolerances for the features that need them, such as a bearing fit, a sealing diameter or a thread, and apply a general tolerance such as ISO 2768-m to everything else.

• Use standard thread sizes and classes rather than special pitches.
• Allow a small radius in internal corners; a perfectly sharp internal corner needs extra operations.
• Avoid very deep, small-diameter holes. Holes deeper than about 8 to 10 times their diameter slow production noticeably.
• Add chamfers on edges and thread starts; they speed assembly and reduce burrs.
• Design hex or flat sections to match standard hexagon bar sizes, so no milling is needed.
• Combine features so the part can be completed in one set-up where possible.
• Tell the supplier your annual volume; the right process for 5,000 parts is often different from the right process for 500,000.