Colleagues:

There is so much more to optomechanics than meets the eye (or ear or touch, even).  I learned a great optomechanical engineering lesson from a Quality Assurance engineer!

Gene was recruited (and offered a “bounty”) by a major manufacturer of lasers for printers to improve the quality of their products, ~1/3rd of which were failing in the 1,000 hour burn-in test.  Gene, in turn, called me in to supplement his electronics industry experience.  (Full disclosure:  We had worked together at one of our previous employers.)

We ran into resistance from both the Mechanical Engineering management and the Factory management.  The mechanical engineers would not let me “review or analyze” any of their design work and the factory would not let me “observe” their operations during working hours.  Hmmm….  Both Gene and I were dumbfounded.  But, I must say that Gene was a resourceful Devil.

He invited me to coffee at a nearby bistro and swore me to secrecy.  Then he laid out his plan:  He would dress me in a white QA smock, give me a clipboard, a jeweler’s loupe, a marking pen and spools of red, yellow and green adhesive dots.  I’d spend most of the day in his office but I’d go out to the factory floor on coffee breaks and lunch times.  I’d cruise the floor, stopping at empty work stations and pretend to inspect the stations, one at a time, applying the loupe and the colored dots (annotating a few, especially the red ones) while making notes on the clipboard.  At the end of each break I’d return to Gene’s office and hide-out.  It took about three days to cover each of the work stations twice.  Then he released me telling me to “disappear.”  I went back to AEH and made myself busy elsewhere.

The next I heard from Gene was a phone call from Norwood, Massachusetts.  The plan worked spectacularly, he had collected his “bounty,” left that company and moved with his family to more stable employment in Norwood.

The laser manufacturer is gone and I think Gene would approve of me sharing his secret with you now.

The lesson?  I think you got it.

Summer’s over and it’s downhill to the Great Pumpkin .  . Shhhhhhhhh!

Al H.
9-13-16

Colleagues:

I was peering into the AEH archives the other day and got a shock.  I needed the source code that I use to analyze the effects of a variety of shock pulse shapes.  What I found was a complete set of mechanical engineering drawings for the medium-weight hammer blow shock test machine at the Hughes-Fullerton facility!  John Martin, who ran the test lab, gave them to me after AEH succeeded in getting a client’s Optical-Nav system qualified for Navy shipboard minesweeper service.

AEH’s job was to specify the shock isolators.  To understand the problem I had prepared a massive Nastran model of the system (6 feet high, two feet square and 550 pounds) mounted on an array of Aeroflex wire-rope isolators.  The numbers had said it should pass the shock test, but it failed.  AEH was called to the lab.  The bolts holding the isolators had stripped the threads in the isolator flanges!  I spent lunch-time with the Nastran output file reviewing the loads and forces and couldn’t make sense of the results.  The client thought that larger/stronger isolators were required.

I went back to the test lab and re-inspected the failed isolator mounts.  I found that the threaded ends of all the failed bolts were flush with the inside surface of their isolator flanges and that all of the un-failed bolt-ends protruded into that sway-space by about 3/16ths of an inch. 

I returned to the Nastran file, looking at displacements in stead of forces.  It predicted that the isolators would use virtually all of their sway-space.  The failed bolts had actually been pushed out when the isolators prematurely bottomed on the bolt-ends, not pulled out when the isolators stretched to their limits.  The bolts were too long.  Larger isolators were not necessary.

One fix was to put extra flat washers under the heads of the bolts so their ends would not protrude into the sway-spaces.  With that accomplished we returned to test the next day and PASSED!

That was AEH’s second successful adventure in John’s shock-test lab.  He graciously offered AEH the drawings for his test machine and invited me to present a paper at the annual conference of the Institute of Environmental Sciences, of which he was President.  I accepted both.

Engineers need to keep their forensic skills sharp, too!

Thank you John Martin!

Al H.
6-1-16

Colleagues:

It’s 2016 so, here we go….

For starters, I moved the AEH offices again.  See the new contact info below. 

Now, I’ve told you the story about the number of rivets in the Queen Mary.  Well here’s one about my calibrated thumb.

Early in my career my boss, Wilford, invited me to the environmental test laboratory.  We found a space payload mounted on the shake table.  He turned to me and asked, “What’s the fundamental resonant frequency of this beast?”  I turned to go up to the Structures Department but Wilford called me back.  He said something like, “We’re the mechanical engineers and should be able to get a pretty good handle on this right here.”

Wilford asked me, “How much do you think it weighs?”  I estimated the dimensions, studied the construction and made a guess.  He raised an eyebrow, but nodded.

Then Wilford walked around the payload and pressed on it several places then beckoned me over suggesting I press on it, which I did.  He asked how much it had moved.  I hadn’t noticed the motion so I pressed again and told him how much motion I had observed.  He asked how hard I had pressed but I had no idea.  He took me to the Inspection Department and had me push on the scales with the same force I’d pushed on the payload.

We went back to Wilford’s office and on his whiteboard he wrote “2 x pi x f = (k/m)^.5,” “k = force/motion” and “m = weight/gravity.”

The next day the test engineer reported that Wilford’s resonant frequency estimate, f, was 3% high.  Not bad.

My estimate wasn’t as good as his but I learned a lesson:  It’s useful for an engineer to maintain a tactile sense of the magnitudes of forces.  I cater to my right thumb.  What about you?

One more tool to keep sharp in 2016.

As I said up-top… “Here we gooooooooo!”

Al H.
1-5-16