Scratch-dig to MIL-O-13830A or MIL-PRF-13830B
gac
I have a question regarding the MIL spec that has become the industry
standard for specifying scratch-dig.
I realise that the scratch number doesn't actually define the width of
scratches (like many people beleive) but references the samples used
for comparison.
According to the drawing C7641866 L, released in 1980, the master
samples have moved from Frankford Arsenal to ARRADCOM. Can you still
get your samples calibrated against the masters as stipulated in Note
6 of the drawing?
If not how do all optics companies keep their scratch sets
calibrated?
Thanks.
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Michael
Recently we've had some (Japanese) vendors insist on an ISO callout rather
than the MIL standard for scratch and dig...
We're told by our main lens vendor (China) that they're seeing 35-40% (and
increasing) ISO format drawings
"gac" <geoffrey...@hotmail-dot-com.no-spam.invalid> wrote in message
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Taff
> standard for specifying scratch-dig.
I would contend that this is the industry standard. It is true that
this MIL spec keeps appearing but in my experience of manufacture of
high end optics this does not apply. I'm a little rusty about the
actual methods used to apply this spec but doesn't it state that it
should be a visual comparison by eye to the scratch/dig standard under
a 40 watt light in a darkened booth viewed at 45 degrees.
If I was to inspect and pass optical surfaces in that manner I'd pass
everything..... Oh wait what am I fighting it for !!??
Taff
Helpful person
>
>
> I would contend that this is the industry standard. It is true that
> this MIL spec keeps appearing but in my experience of manufacture of
> high end optics this does not apply. I'm a little rusty about the
> actual methods used to apply this spec but doesn't it state that it
> should be a visual comparison by eye to the scratch/dig standard under
> a 40 watt light in a darkened booth viewed at 45 degrees.
> If I was to inspect and pass optical surfaces in that manner I'd pass
> everything..... Oh wait what am I fighting it for !!??
>
> Taff
If I remember correctly the lamp specified in the MIL spec has not
been available for many years.
Steve Eckhardt
mb...@light-deletedashtodash-houseoptics.com says...
>
>Doesn't address your question directly, but....
>
>Recently we've had some (Japanese) vendors insist on an ISO callout rather
>than the MIL standard for scratch and dig...
>We're told by our main lens vendor (China) that they're seeing 35-40% (and
>increasing) ISO format drawings
Wow! Either I'm buying more optics than I thought, or someone else is using
the Internationally Recognized but universally unrecognized standard.
As far as the MIL scratch/dig spec, Jean Bennet argued years ago that it was a
purely cosmetic spec. If you use it that way, it works well. For instance,
if I want laser optics, I spec 20/10, but if I only need commercial grade, I
order 80/50. Condensers are 120/80, etc.
Just for total confusion, I spec the scratch/dig on my pseudo-ISO prints as
5/80/50!
--
Best regards,
Steve Eckhardt
skeckhardt at mmm dot com
Brian Blandford
> Doesn't address your question directly, but....
>
> Recently we've had some (Japanese) vendors insist on an ISO callout rather
> than the MIL standard for scratch and dig...
> We're told by our main lens vendor (China) that they're seeing 35-40% (and
> increasing) ISO format drawings
IMHO the ISO 10110 equivalent for 80-50 is 5/1x0.5;L1x0.008.
Brian B
gac
From my understanding the inspection is, as you mentioned, with a 40W
light bulb etc.
Also, as I read the spec, the scratch number is very subjective and is
a comparison to standard samples. However the dig number does relate
to the actual width of the dig. The drawing I mentioned in my first
post describes how to make the set of samples. This drawing has had
many revisions that state many different things ie, "Scratch numbers
do not denote width of scratch. The numbers indicate that the
scratch has the same weight or visual appearance as the master
scratch bearing the same weight number", "Scratch number denotes
width of scratch in microns", "#10 Scratch = 1um +/- 0.1....", and
the ever popular "Dimensions are for reference only". Anyway as I
understand these dimensions on the drawing should be used as a guide
to preparing your samples but they must be calibrated against the
master set.
Perusing different websites and optics suppliers shows that everyone
wants to link the scratch number to a width. Some go with the 10 =
10 theory and some go with the 10 = 1. My original question on the
master samples was due to these two different schools of thought ie
can anyone do the correct calibration or are companies just measuring
the width of their standard samples and saying they are calibrated?
If it is the latter then the scratch criteria has changed to reflect
MIL-F-48616 - which allows for the actual measurement of the width of
the scratch but uses letters instead of numbers eg F-F.
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gac
> gacwrote:
> According to the drawing C7641866 L, released in 1980, the master
samples have moved from Frankford Arsenal to ARRADCOM. Can you still
get your samples calibrated against the masters as stipulated in Note
6 of the drawing?
>
> If not how do all optics companies keep their scratch sets
calibrated?
>
>
Information from OEOSC (who are developing a new standard due out
early next year) indicate that the old scratch dig comparison
standard is carrying over to the new standard.
DonJan
Another question: Have the master standards changed with time? Do the
fine scratches close up?
gac
Another question: Have the master standards changed with time? Do
the
> fine scratches close up?
This comes from the paper, "The Scratch Standard Is Only A Cosmetic
Standard" by Matt Young.
"Additionally, the startling factor-of-10 change between Revisions H
and L has caused some users to speculate that the primary standards
may have healed with the passage of time. Certainly the glass around
a scratch cannot flow (the viscosity of glass at room temperature is
well in excess of 10^15 Pa*s), but chemical weathering of the surface
due to water vapor in the air is a possibility and could cause the
primary standard either to heal or to worsen. There is evidence,
however, that most weathering would take place and stabilize within a
few hours or days. In any case, a change has to be quite substantial
before it is apparent to the naked eye and, I think, would be picked
up by the trained inspectors when they make repeated comparisons with
secondary standards. More probably, it seems to me, small scratches
that are reported to have "disappeared" have been contaminated by the
volatile constituents of their wooden boxes and merely required a good
degreasing,"
Anyway it is the drawing that has changed with time, due to peoples
attempts to define the scratch number as a width. Revision H of the
drawing was the first define the scratch number as the width of the
scratch in microns and also that calibration back to the masters is
not essential. However Revision H was quickly surperceeded two years
later by Revision J which said the scratch width was one tenth the
scratch number and all manufacturer generated standards must be
calibrated against the master set. In any event nothing in the
certification procedure had changed, nor has it changed to this day.
Remember that a certified set of submasters is boxed but not
hermetically sealed and therefore it must be resubmitted periodically
for recertification - hence my question can you still get comparison
standards certified against the masters?
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