In my column last week, I asked, "Have dimensional mistakes ever affected your area of responsibility?"
Half of the respondents answered, "Yes, sometimes," 30 percent said "Yes, often," and 20 percent answered "Yes, rarely." No one selected "No, never," or "Yes, many times."
Next, I asked, "Any dimensional errors you wish to share?"
Responses:
>Early in my engineering career I didn't check the clearance between stairs along side a pulper feed apron conveyor Vs. the building steel. A Vice-president said, That is one mistake...three and you are gone." I learned the importance of being aware of what other disciplines are doing around your equipment.
>One time early in my career, when I was a design engineer, I had done the drawings for a new base for a thick stock pump in the bleach plant. I checked and double checked the math on all of the dimensions (this was WAY before Autocad) and the base was fabricated and parts ordered. During the annual shutdown, the base was changed and lo and behold, the pump shaft and gearbox shaft were too far apart for the coupling. Fortunately a half spacer coupling solved the problem and when I went back and re-checked the dimensions I discovered that I had made a mistake converting inches to feet and inches (why don't we go metric and make things so much easier). Yes, dimensions can be very critical!!!
>As with you, one of my early jobs was to do with dimensions. I the days before computers and especially CAD we manually designed flowbox manifolds. Given that the flows, viscosities etc are rarely within the bands specified for long and the steel fabricators would only allow 3 planes this was part maths, part physics and a lot of art. On one project come start-up, with 30 people waiting for paper from the reel as always, it quickly became apparent that profile was awful. We concluded that for some reason, at the flows they needed, the entry direction to the flowbox was not 90 but 45 degrees. Few options available, no going back to old box, we reversed the perforated plate. We were off the hook - best profiles ever. Never knew what went wrong, rechecked calculations several times. Not really dimensional, as we were correct, but if plate change hadn't worked and mill was shut until another manifold made our calculations would have been the key factor on who paid the massive cost. Thanks for a great column every week.
>We faced problem due to pressure screen basket bolt slots not matching with the original bolts on the rotor.
>I recollect my father had a bridge beam that fitted nicely between the trestles. I have commonly encountered calculations where values in metric have been included with others in American. Also, because so many calculations are in spreadsheets the check of writing out the units and ensuring that with all the divisions and multiplications the answers have the intended unit. This alone cuts my errors significantly.
Take the current quiz here.
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