Scratch / Dig Specifications
Purpose:
This document defines glass surface
quality on optical components per MIL-O-13830.
Definitions:
SCRATCH: Any marking or tearing of the
glass surface.
SLEEK SCRATCH: A hairline
scratch.
CRUSH or RUB SCRATCH: A surface scratch
or a series of small scratches.
DIG: A small rough spot on the glass
surface similar to pits in appearance. A bubble is considered a
dig.
Procedure:
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 .0024 inches
and a dig diameter of .0158 inches. The size of a defect is to be
measured through the use of an optical comparator.
|
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 | 0.040 |
| 05 | 0.005 | 0.0002 | 0.05 | 0.0020 | 1 | 0.040 |
| 03 | 0.003 | 0.00012 | 0.03 | 0.0012 | 1 | 0.040 |