Scratch / Dig Optical Surface Specifications

Purpose:
This
document defines surface quality on optical components per
MIL-O-13830.

Definitions:

SCRATCH: Any marking or tearing of the part surface.

DIG: A small rough spot on the part surface similar to a pit in
appearance. A bubble is considered a dig.

SLEEK SCRATCH: A hairline scratch.

CRUSH or RUB SCRATCH: A surface scratch or a series of small
scratches.

Method:
The size of a defect is to be measured through the use of an optical
comparator:
Surface quality is to be specified by a number such as 60/40.
The first digits relate to the maximum width allowance of a scratch as measured
in microns. The next digits indicate to maximum diameter allowance for a dig in
hundredths of a millimeter. Thus, as can be seen from the table below, a surface
quality callout of 60/40 would permit a scratch width of .06 mm (60 micron -or-
0.0024") and a dig diameter of .40 mm (400 micron -or- 0.0158").

Scratch
or
Dig Number

Maximum
Scratch
Width

Maximum
Dig
or Bubble Diameter

Dig or
Bubble
Separation Distance

#

mm

inch

mm

inch

mm

inch

120

0.12

0.0047

1.20

0.0473

20

0.787

80

0.08

0.0031

0.80

0.0315

20

0.787

60

0.06

0.0024

0.60

0.0236

20

0.787

50

0.05

0.0020

0.50

0.0196

20

0.787

40

0.04

0.0016

0.40

0.0158

20

0.787

30

0.03

0.0012

0.30

0.0118

20

0.787

20

0.02

0.0008

0.20

0.0079

20

0.787

15

0.015

0.0006

0.15

0.0059

20

0.787

10

0.010

0.0004

0.10

0.0039

1.0

0.040

5

0.005

0.0002

0.05

0.0020

1.0

0.040

3

0.003

0.00012

0.03

0.0012

1.0

0.040

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