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Micros

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Dave G

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Posting on my twin build about finishing with sandpaper got me to thinking about when I was an apprentice. We apprentices got to spend a few months in the metalurgy dept where I worked. We were a bearing manufacturer that used many types of steels in our bearings. We did our own heat treating and this is what my father did for many years there. Needless to say when the only hourly guy that could run every furnace in the place's kid got to spend time in the met lab he got the red carpet treatment. One of the things that they did was to check the structure of the steel after heat treating. Very important when you don't want a wheel to fall off your car. To do this we made what they called micros. You cut a section of the part away that you wanted to check and set it in with a powder that when heated and compressed it would form a disk about 1.5" in dia and about 1" tall. The metal piece would be suspended in the disk. Then you had to sand the surface you wanted to check to a mirror finish.

Once the surface finish was good enough the micro would be placed into a micrscope to be looked at. Now I should have paid better attention at what they were doing but mind you I think I was 20 at the time. The most I can remember is the head metalurgist, who was a very smart fellow of Italian descent, and commanded a great amount of power, was very picky with the quality of the finish on the micros. If the finish wasn't good enough it was sometimes hurled at you accompanied with a verbal insult to the quality of your usefulness. You didn't want to be on the wrong end of this to many times. I quickly learned how to sand to very fine finish at a very young age. I never got a micro hurled at me but I do remember having to duck for cover a couple of times.

Turning the part so the sand scatches could be seen from the previous grit was a good way to do it. You needed to completely remove the scratches with the grit you were using before going to the next finer grit. We used a sanding table made by a company called Bueller I think. It had water running over it to help the paper from clogging. I think this is where my finishing skills were formed, and its amazing how fast one can learn a skill sometimes.

The head metalurgist was an avid golfer. He was notorious for calling everyone in the office before lunch on every friday and giving every one of his metalugists a complete dressing down. We apprentices were spared the tirade but got to watch and he sometimes would tell me to keep an eye on them for him as he headed out to play his 18.

Anyone else ever made micros? Dave
 

ProdEng

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Hi Dave,

I had the same experience, I worked at a place that made truck axles and we heat treated all the gears. In addition to preparing samples for microscopic examination we also got to measure the hardness profile of case hardened gears. You had to do a hardness test at specified increments from the outside of the gear, the hardness tester had a microscope and a graticule. Back to the polishing, the diamond polisher was the most fun, spraying too much acetone on it and filling the room with lovely smelling vapour; really dumb I know ::)
 

Dave G

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A quick check we did with case hardened parts was to cut a section and polish it. Then the surface was treated to a sulfuric acid bath and the acid would etch the metal. The difference in hardness would show up a different shade that could be measured to find the depth of the case hardening. Dave
 

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