CNC Machining Tolerance Reference

Size Range

(mm)

Precision Grade

(IT6-IT7, e.g. molds, aerospace)

Economic Grade

(IT8-IT9, general parts)

Rough Grade

(IT10-IT12, roughing or as-cast)

0.5 - 3

±0.005 ~ ±0.010 

±0.05 ~ ±0.10

±0.10 ~ ±0.20

3 - 6

±0.008 ~ ±0.015

±0.05 ~ ±0.10

±0.15 ~ ±0.30

6 - 30

±0.010 ~ ±0.020

±0.10 ~ ±0.20

±0.20 ~ ±0.50

30 - 120

±0.015 ~ ±0.025

±0.15 ~ ±0.30

±0.30 ~ ±0.80

120 - 400

±0.020 ~ ±0.035

±0.20 ~ ±0.50

±0.50 ~ ±1.20

400 - 1000

±0.030 ~ ±0.050

±0.30 ~ ±0.80

±0.80 ~ ±2.00

Standard drilling

IT12-IT13

All

±0.10 ~ ±0.25 (general locating holes)

Standard reaming

IT7-IT8

1 - 20

+0.010 ~ +0.030 (H7 basis)

Reaming / Fine boring

IT6-IT7

20 - 50

+0.015 ~ +0.025 (H7)

CNC precision boring

IT5-IT6

50 - 120

+0.010 ~ +0.020 (high precision)

▱

Flatness

0.02 / 100mm

0.02 mm deviation per 100mm length

─

Straightness

0.01 / 100mm

Bending per 100mm of shaft or edge

⟂

Perpendicularity

0.03 / 100mm

Tilt of end face relative to axis

∥

Parallelism

0.02 / 100mm

Parallelism between two planes or axes

◎

Coaxiality / Concentricity

φ0.025

Diametrical offset of two cylindrical axes

○

Roundness

0.008

Deviation from perfect circle

Standard CNC milling

±0.010 mm

±0.005 mm

IT8-IT9 (±0.05~0.10mm)

Mid-range VMC

±0.008 mm

±0.004 mm

IT7-IT8 (±0.02~0.05mm)

High-precision machining center

±0.005 mm

±0.002 mm

IT6-IT7 (±0.008~0.015mm)

Economy CNC lathe

±0.005 mm (axial)

±0.003 mm

IT7-IT8 (±0.01~0.03mm on OD)

5-axis machining center

±0.005 mm

±0.002 mm

Complex surfaces ~ IT7