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CNC Machining Tolerances Tables

Time:2021-05-31 Views:409

When specifying parts to a machine shop, it‘s important to include any necessary tolerances. Though CNC machines are very accurate, they still leave some slight variation between duplicates of the same part, generally around + or - .005 in (.127 mm), which is roughly twice the width of a human hair. To save on costs, buyers should only specify tolerances in areas of the part that will need to be especially accurate because they will come into contact with other parts. While there are standard tolerances for different levels of machining (as shown in the tables below), not all tolerances are equal. If, for example, a part absolutely cannot be larger than the measurement, it might have a specified tolerance of +0.0/-0.5 to show it can be slightly smaller, but no larger in that area. 

Table 1: Linear Tolerances in CNC Machining

Dimension Range (mm)

Fine (F)

+/-

Medium (M)

+/-

Coarse (C)

+/-

Very Coarse (V) +/-

.5-3

.05

.1

.2

--

3-6

.05

.1

.3

.5

6-30

.1

.2

.5

1.0

30-120

.15

.3

.8

1.5

120-400

.2

.5

1.2

2.5

400-1000

.3

.8

2.0

4.0

1000-2000

.5

1.2

3.0

6.0

2000-4000

--

2.0

4.0

8.0

 

Table 2: Angle Tolerances in CNC Machining

Dimension Range (mm)

Fine (F)

+/-

Medium (M)

+/-

Coarse (C)

+/-

Very Coarse (V) +/-

0-10

1o

1o

1o 30’

3o

10-50

0 o 30’

0 o 30’

1o

2o

50-120

0 o 20’

0 o 20’

0 o 30’

1o

120-400

0 o 10’

0 o 10’

0 o 15’

0 o 30’

400

0 o 5’

0 o 5’

0 o 10’

0 o 20’

 

Table 3: Radius and Chamfer Tolerances in CNC Machining

Dimension Range (mm)

Fine (F)

+/-

Medium (M)

+/-

Coarse (C)

+/-

Very Coarse (V) +/-

.5-3

.2

.2

.4

.4

3-6

.5

.5

1

1

6

1

1

2

2