Planning Machining Allowance the Economical Way
Why stock cannot be zero
The casting skin carries surface texture and, immediately beneath it, the densest or most variable material depending on process conditions. Machined features therefore need stock to cut past surface variation and hold tolerance on true material. Too little stock and the tool skims skin, accelerating wear and risking tolerance misses; too much and cycle time, tool wear and porosity exposure all grow.
Typical allowances on moderately sized die castings run from a few tenths of a millimetre to around one millimetre per face, growing with feature size and with the precision required after machining.
Datum strategy decides the outcome
Machining quality depends on how the casting is located. Datum features should be cast surfaces chosen to be stable, repeatable and away from gates and overflows. The casting-to-machining interface is best designed together: datum targets on the print, machining stock stated per face, and tolerances split sensibly between as-cast and machined dimensions.
When datum and stock plans are missing, every supplier guesses, and results vary. When they are explicit, quotes get sharper and first articles pass faster.
Practical checklist for drawings
State which faces are machined, give per-face stock or a machining note, define datum targets on cast surfaces, mark thread depths so tool clearance survives the skin condition, and specify any leak-test or X-ray requirement that constrains machining depth.
Our quoting team reviews customer drawings against exactly this list and returns machining-friendly DFM comments before tooling is cut.
FAQ
How much machining stock should I allow on my die casting?
As a starting range, 0.3–1.0 mm per machined face for typical part sizes, adjusted for casting size, feature depth and final tolerance. Exact values are confirmed in DFM review.
Why not cast to final size and skip machining?
Some features can be net-shaped, but precision bores, sealing faces and threads usually need machining for tolerance and surface finish. The economic mix is decided feature by feature.
Does machining into porosity cause rejects?
It can reveal porosity inside the section. That is why machining depth, X-ray criteria and shot parameters are coordinated for critical parts instead of being decided independently.
Can you machine die castings in-house?
Yes, machining of die castings is a standard in-house capability, covering facing, drilling, tapping, reaming and milling operations per the customer print.
All figures above refer to standard product data sheets; final confirmation is subject to written quotation.