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Machining surface finish chart, comparator, method, degree, Ra, Rz, RMS

As for machining to iron and steel castings, the surface finish smooth degree is also an important requirement. The following is the conversion chart for Ra (um), Ra (micro inch), Rz (um), RMS and finish degree in China and USA, including the related finish methods.

China
Finish Degree

China
Ra (um)

China
Rz (um)

USA
Ra (um)

USA Ra
(micro inch)

USA RMS
(micro inch)

Machining Finish Method

1

50

200

50.0

2000

2200

The most coarse machining or good rough casting surfaces

2

25

100

25.0

1000

1100

Machining marks very obvious.
Rough turning, boring, planning, drilling.

3

12.5

50

12.5

500

550

Machining marks obvious.
Rough turning, planning, milling, drilling.

4

6.3

25

8.00

320

352

Machining marks visible.
Normal turning, boring, planning, drilling, grinding.

6.30

250

275

5

3.2

12.5

5.00

200

220

Machining marks not obvious, but still visible.
Normal turning, boring, planning, drilling, grinding.

4.00

160

176

3.20

125

137.5

6

1.6

6.3

2.50

100

110

Machining marks blur, but marks direction obvious.
Number controlled turning, boring, planning, drilling, grinding.

2.00

80

88

1.60

63

69.3

7

0.8

6.3

1.25

50

55

Machining marks direction blur, but still visible.
Number controlled turning, boring, planning, drilling, grinding.

1.00

40

44

0.80

32

35.2

8

0.4

3.2

0.63

25

27.5

Machining marks direction blur.
Reaming, grinding, boring, rolling.

0.50

20

22

0.40

16

17.6

9

0.2

1.6

0.20

12.5

13.75

Machining marks direction invisible.
Grinding, super machining.

10

11

8

8.8

10

0.1

0.8

0.10

4

4.4

Surface dark gloss.
Super machining.

The photos of surface finish comparator for milling, turning, reaming and grinding

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