Most expensive machining features are not obviously expensive in CAD. They simply require smaller tools, more passes, extra set-ups or slower cutting. The list below covers the details that most often surprise designers when a quote comes back higher than expected.
1. Sharp internal corners
A rotating end mill leaves a radius in every vertical internal corner. A sharp corner requires a very small tool or a secondary operation such as EDM. Specifying a corner radius that is at least one third of the cavity depth — or simply allowing a radius — removes that cost.
2. Over-tolerancing
Every tight tolerance adds measurement time, slower cutting and scrap risk. Apply tight values only to features that affect function and let a general shop tolerance cover the rest.
3. Deep cavities and deep holes
Deep pockets need long-reach tools, which deflect and must cut slowly. Depth-to-width ratios above roughly 4:1 become progressively more difficult. Deep small-diameter holes are slower still because chips must be evacuated.
4. Thin walls and thin floors
Thin sections vibrate, deflect and can distort from cutting heat and material stress. Minimum wall thickness depends on the material: aluminium can usually be thinner than steel, and plastics need more thickness than metals.
5. Features on multiple faces
Every additional face that needs machining can mean another set-up. Consolidating features onto fewer faces, or designing so that one clamping covers more work, is one of the cheapest changes available.
6. Very small features
Small pockets and tiny holes require small tools that break easily and cut slowly. Where a feature does not affect function, enlarging it slightly often reduces cost noticeably.
7. Unnecessary cosmetic requirements
Requiring a uniform cosmetic finish on every face means extra polishing and handling. Mark which faces are visible in the final assembly and finish only those.
8. Threads without a clearance or run-out
Blind tapped holes need drill depth beyond the thread and a run-out for the tool. Very fine or non-standard threads may also require special taps. Standard metric or unified sizes are faster and cheaper.
Summary: None of these details make a part impossible — they make it slower. A short manufacturability review before quoting is usually enough to remove most of the cost without changing the design intent.
Need parts made to your drawing?
Request a quote