Understanding MIM Tolerances: From ±0.5% to ±0.3%

The most common question in any MIM feasibility review is tolerance. The short answer: as a general rule MIM holds ±0.5% of the dimension, and smaller dimensions can be controlled to ±0.3%. The long answer is a table, because capability scales with size.

For dimensions of 1–4 mm the general tolerance is ±0.05 mm, with ±0.03 mm achievable in special cases. From 4–10 mm the figures are ±0.07 mm general and ±0.05 mm special. From 10–20 mm, ±0.10 mm general and ±0.08 mm special. From 20–30 mm, ±0.15 mm general and ±0.1 mm special. From 30–50 mm, ±0.25 mm general and ±0.2 mm special. Above 50 mm, tolerances are expressed as a percentage: ±5‰ general and ±3‰ special.

Beyond dimensions, two physical limits define the MIM envelope. Part weight typically ranges from 0.01 g to 1000 g — parts over 2 kg are not suitable for the process. Wall thickness generally runs from 0.1 mm to 10 mm, and thin walls below 0.2 mm that defeat both machining and conventional pressing are precisely where MIM shines.

What decides whether you land at the general or the special end of the table? Powder consistency, feedstock homogeneity, mold precision, debinding and sintering shrinkage control, and — when a critical dimension must be tightened further — a sizing operation with a dedicated sizing mold. If a drawing still exceeds these limits, targeted CNC finishing of individual features is the standard fallback.

When you send drawings for evaluation, mark the critical dimensions and their required tolerances. Our engineers will tell you which can be held as-sintered, which need sizing, and which need a secondary machining step — before any tooling money is spent.