Something for you die hard polishers out there to chew on

[thesound]

Check out the picture of the piece of aluminum bar stock in this article:

http://www.nasatech.com/Briefs/Feb01/GSC14147.html

I've seen several posts throughout this forum in the past about guys who had exhausted all sandpaper grits, gone through all the various compounds, and after it was all said and done there were still tiny scratches that would show up on the part when looked at from the right angle and under the right kind've light. My guess is after looking at this process Nasa used with India Ink, and seeing the end result, maybe this last step might be worth the extra trouble? (I mean heck, if you're already soiled from compound gunk flying around, what's a little ink gonna hurt? )

Just out of curiosity has anyone here ever experimented with this stuff?

-Rob-

[pickleboy]

Originally Posted by thesound

Just out of curiosity has anyone here ever experimented with this stuff?

-Rob-

thanks for the link bro.
i have never heard of this but i will sure research it more. i only wonder where to get the diamond dust and what is the exact process (is it polished by hand, machine or what)? this is very interesting.

[mpierich]

Wow, that looks impressive. Thanks for posting it.

I was just about to post a rant on getting those daggone mico-scratches out, but this article seems to be saying that it's impossible on soft aluminum, using our techinques. It's pretty hard to convince a customer that your work is "perfect" when they see these scratches in bright sunlight (although in reality I haven't had any actual complaints yet - you almost have to be looking for them to see them. I've actually pointed them out and people are like, "so? looks good to me...").

I wonder what tool would be used with the ink...loose wheels? Some kind of synthetic burnisher? If the article said this I missed it.

This also explained to me why we get those micro-scratches - the softness of the aluminum. I haven't done enough stainless to know better, but seems to me that this wouldn't be a problem with stainless if hardness is the deciding factor.

Anybody else done a lot of stainless? Any difference in the micro-scratches?

[thesound]

I went into the archives section of that NASA site and downloaded the technical support package that explains in more detail about this:



Goddard Space Flight Center
Greenbelt, Maryland 20771
Technical Support Package
Process for Polishing Bare Aluminum to High
Optical Quality
NASA Tech Briefs
GSC-14147
National Aeronautics and
Space Administration
Technical Support Package
for
PROCESS FOR POLISHING BARE ALUMINUM TO
HIGH OPTICAL QUALITY
GSC-14147
NASA Tech Briefs
The information in this Technical Support Package comprises the documentation
referenced in GSC-14147 of NASA Tech Briefs. It is provided under the Commercial
Technology Program of the National Aeronautics and Space Administration to make
available the results of aerospace-related developments considered to have wider
technological, scientific, or commercial applications. Further assistance is available
from sources listed in NASA Tech Briefs on the page entitled “NASA Commercial
Technology Team.”
Additional information regarding research and technology in this general area may be
found in a variety of publications available from the NASA Scientific and Technical
Information (STI) Program Office. You can access the STI Program Office via
http://www.sti.nasa.gov or as follows:
NASA STI Help Desk
NASA Center for AeroSpace Information
7121 Standard Drive
Hanover, MD 21076-1320
Telephone: (301) 621-0390, Fax: (301) 621-0134, E-mail: help@sti.nasa.gov
NOTICE: This document was prepared under the sponsorship of the National Aeronautics and Space
Administration. Neither the United States Government nor any person acting on behalf of the United
States Government assumes any liability resulting from the use of the information contained in this
document or warrants that such use will be free from privately owned rights. If trade names or
manufacturers’ names are used in this report, it is for identification only. This usage does not constitute an
official endorsement, either expressed or implied, by the National Aeronautics and Space Administration.


Process for Polishing Bare Aluminum to High Optical Quality


BRIEF ABSTRACT
A revolutionary new technical advancement in the field of precision aluminum optics
has permitted high-quality optical “super-polishing” of aluminum substrates.
Aluminum materials are used worldwide for many applications throughout the
aerospace and science communities. In the area of optics, aluminum offers numerous
benefits because of its machinability, light weight, and low cost. Until single point
diamond turning was developed in the 1970’s, there were no means of producing a
conventionally polished surface on aluminum that was applicable for optical use.
Diamond turning is still the main means of satisfying this requirement; however, this
process is limited because of accuracy limitations of the diamond turning machine.
Under optimum conditions, diamond turning is limited to producing surface with
microroughness levels of 50–100 angstroms or greater, and surface figure performance
of approximately 0.5 to 0.75 of a wave with one wave being 6,328 angstroms.
The proposed invention is a revolutionary process for the precise optical polishing of
typical bare aluminum material to a microroughness of less than 6 angstroms RMS,
while maintaining a surface figure accuracy of 0.125 of a wave peak-to-valley.


SECTION I – DESCRIPTION OF THE PROBLEM

In the world of optics, optical instruments, satellites, and interferometry, system performance is
largely dependent on the actual reflective surface of a given optic. The performance of the optical
mount and its thermal and mechanical characteristics also influence the performance of the
component it supports, which in turn, has a very large impact on the entire system performance
and on the success of the scientific project. Many spacecraft systems utilize aluminum materials
for structures and in cases of cold/cryogenic use could utilize aluminum mirrors as well. This
works well in theory, except for the fact that aluminum cannot be readily polished to a smooth
enough surface to make it an acceptable optic (due to scatter) for UV, IR, and visible spectrum.
Current technology attempts to resolve this problem by electroplating a thin layer of electroless
nickel to the entire component surface and then optically polish the plated nickel. The result creates
a trade-off whereby surface microroughness is decreased while thermal and mechanical stability of
the optic are severely compromised at all but room temperatures. This is especially true for
-1- GSC-14147
aluminum optics that have been light-weighted. Material removal or “pocketing” of the back
surface of a mirror means that there is several times more surface area to plate than on the front.
Complicating matters even more is that the mount is usually an integrally machined part of an
aluminum optic. While these characteristics are great for dimensional requirements and ease of
design, they create havoc on the optical performance once all surface are evenly plated with nickel.
Successfully developing a method of optically polishing bare aluminum mirrors to super-smooth
surface eliminates the need for adding electroless nickel platings, thus eradicating performance
deterioration resulting from bi-metallic stresses.


SECTION II – TECHNICAL DESCRIPTION

The proposed innovation presents a novel and new technique of optical polishing aluminum
substrate materials in a conventional polishing manner by employing modern techniques with a
combination of compatible ingredients. Polishing is performed by the precise assembly of
components to create a working tool-holding apparatus. To start, a select grade of pitch used
exclusively for optical fabrication is melted and poured onto a cast-iron lap. It is allowed to cool
and then shaped and grooved according to the optician’s judgement. This is generally referred to
as “a polisher.” Once complete, it is installed on the machine spindle. The optician then applies the
appropriate amount of polishing compound and liquid carrier (such as water) to the pitch surface,
and places the optical component onto the assembly. (These ingredients differ according to the
material being polished.) The pivot pin is then lowered into a small hole which is pre-drilled in the
back of the optic and the assembly is set into motion. This method of polishing is called random
motion polishing. As the machine spindle rotates, the polisher and the floating optic also rotate,
while the pivot pin passes back and forth over the polisher at a predetermined distance. The
geometry is such that all points of the polisher and all points of the optic “see” the same amount of
surface feet per minute of contract, resulting in even material removal. This process is performed
until an acceptable surface figure and roughness are achieved. This procedure is well established
for materials such as glass, nickel, stainless steel, and many other glass or metal materials. Until
now, it has been internationally recognized that there are no known means of conventional
polishing, or combination of polishing methods which would successfully polish bear aluminum
materials. (This was a thoroughly discussed topic at the 1999 SPIE conference of cryogenic
optical systems in San Diego, CA.)
The significant of the new technique differs from conventional polishing technique described above
whereby the materials used as a polishing compound and carrier are completely different from that
-2- GSC-14147
of normal polishing materials. The innovative technique employs “Black Water-Proof India Ink”
by KOH-I-NOOR (or equivalent) as a combined compound/lubricant carrier. What makes this so
successful is that black india ink contains small particles of carbon which are very hard yet small
enough to provide the correct action between the surfaces of the optic and polisher so as to not
cause severe scratching or cold material flow. The liquid portion of the ink, which is an oily base,
provides terrific lubrication while polishing. After years of extensive experimentation with all
known conventional polishing materials and combinations thereof, this material properly used in a
conventional manner is the only known substance to produce a successful polish on bare aluminum
materials.


SECTION III – UNIQUE OR NOVEL FEATURES

The uniqueness of the proposed innovation permits superior polishing of bare aluminum materials
to surface qualities of 5–6 angstroms RMS or less microroughness, with a surface figure error as
low as one-eighth (0.125) of a wave peak-to-valley. The implementation of this invention in
NASA alone would result in major cost and schedule savings of instruments currently baselining
aluminum optical components. As employees of Goddard’s optics branch, the inventors have
extensive experience in aluminum optics technology, cryogenic operation and characterization and
system wavefront performance effects of aluminum optics plated with electroless nickel. It is a
known fact industry-wide that all aluminum mirrors with requirements tighter than that which can
be delivered by diamond turning MUST have an electroless-nickel plating. Completely eliminating
this step will mean the following:
• Drastic savings during fabrication by eliminating electroless nickel plating steps.
• Less polishing time (nickel is harder to polish).
• Reduced risk associated with polishing through nickel to the aluminum. This requires that the
part be stripped of the remaining nickel and re-plated. To do so, the optical surface must again
be prepared for plating because the stripping procedure etches the aluminum.
• Drastic performance improvements. It is known that properly heat-treated bare aluminum
performs well in cryogenic conditions without the nickel plating.
• Reduced cost of final component characterizations. Plated mirrors that show abnormalities are
often tested and re-tested to determine the impact on the system performance. If the problem is
-3- GSC-14147
identified to be with the nickel plating as is often the case, then the process must be completely
repeated by stripping the mirror and starting over.
There are several risks associated with fabricating aluminum mirrors using the prior methods that
have been discussed. The Composite Infrared Spectrometer (CIRS) which was flown aboard
Cassini literally spent hundreds of thousands of dollars in a feeble attempt to characterize an
existing telescope system only to determine that it could not be used because of the bimetallic
stresses present in the telescope. The aluminum Relay Optics also used in CIRS often drove the
schedule of the flight instrument build because of problems with cryogenic performance caused by
the nickel stresses. Most recently, Infrared Array Camera (IRAC) and the Development Cryogenic
Active Telescope Testbed (DCATT) have experience schedule delays and drastically increased cost
associated with aluminum mirrors and electroless nickel plating.
Properly implemented, the proposed innovation will eliminate many of the associated problems
now common with current aluminum-mirror technology.


SECTION IV – POTENTIAL COMMERCIAL APPLICATIONS

This new innovation will revolutionize the way industry, the department of defense, NASA and all
outside optical alignment, fabrication, and test organizations design optical systems and
components for space flight or ground-based systems. This could result in as much as fiftypercent
savings to engineering, design, fabrication, and characterization cost of a given assembly
of components or system.
The commercial potential for this invention is extremely high and would be very beneficial to
NASA and its missions as this technology takes form and is brought back into the agency through
superior aluminum optical components.


SECTION V – REFERENCE

Lyons, James, III and Zaniewski, John, “Process for Producing High Quality Optically Polished
Surfaces on Bare Aluminum Substrates,” GSFC Technology Assessment Report, RTI-98-G016;
GSC-14147-1, November 3, 1998.
-4- GSC-14147

[mpierich]

Originally Posted by thesound

I went into the archives section of that NASA site and downloaded the technical support package that explains in more detail about this:

Thanks. To me, using conventional equipment with India ink presents obvious problems; i.e., throwing the ink off the polishing device.

I wonder if it would work with something like a rotary cup buff used at _very_ low speed, perhaps using a good bit of pressure as a substitute for speed...

This definitely bears further investigation and experimentation. I've tried everything from blue compound to talcum powder to kerosene to get rid of those damn scratches.

The hardness thing still intrigues me. It would explain why chrome doesn't have the scratches.

[thesound]

Thanks. To me, using conventional equipment with India ink presents obvious problems; i.e., throwing the ink off the polishing device.

I wonder if it would work with something like a rotary cup buff used at _very_ low speed, perhaps using a good bit of pressure as a substitute for speed...



It's feasible if you did it inside of a blasting cabinet. I'm thinking that if you totally submerged a loose cotton wheel in this stuff, to the point that it was sloppy wet, you could keep an adequate amount of ink particles in contact with the surface by periodically adding more pressure and squeezing more out of the buff as if you were wringing out a wet mop. (The wringing effect would continue to get easier as you continued to dilute the ink with distilled water.)

[mpierich]

Originally Posted by thesound

It's feasible if you did it inside of a blasting cabinet. I'm thinking that if you totally submerged a loose cotton wheel in this stuff, to the point that it was sloppy wet, you could keep an adequate amount of ink particles in contact with the surface by periodically adding more pressure and squeezing more out of the buff as if you were wringing out a wet mop. (The wringing effect would continue to get easier as you continued to dilute the ink with distilled water.)

Need to use an enclosure for sure. Maybe even do it in a tray of some kind where you keep the surface flooded with the stuff.

All my polish look's that way..

[mpierich]

Originally Posted by customandsound

All my polish look's that way..

I hear ya!

[easleysp]

My partner at work used to make paper products at a plant here in town a few years back. I was telling him about this new process and he said they used to make their own carbon paper by using India ink and that he thought the roller that was always in contact with the ink was a chrome roller. They had to change out the roller after a while and discovered it wasn't chrome, just plain carbon steal. He said now he understands why it was so shiny. Just thought I'd share that with ya'll.

Steve