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Quick Reference: Tooling Tolerances

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Charles Murray
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Blogger
Great article
Charles Murray   1/18/2013 4:58:12 PM
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This author should make a tour of some of his local colleges and talk to engineering students who are overloaded with theoretical mechanics classes and don't get ANY exposure to manufacturing. As a result, too many new engineers don't know how to design for manufacturability. This kind if insight is invaluable.

tekochip
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Platinum
Over Specified
tekochip   1/18/2013 7:09:44 PM
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Thanks for the article.  I have seen otherwise capable engineers specify ridiculous tolerances over and over again without realizing the cost attached to those tolerances or the assembly problems they produce.  I had one engineer that specified a 7.000" part to fit into a 7.000" slot.  Not only was the part in no way not critical, but the parts wouldn't fit if one came from the cold warehouse.  No matter how hard I tried, he just couldn't understand why it was a problem.

GlennA
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Gold
default tolerances
GlennA   1/19/2013 9:12:03 PM
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I tried to explain to a mechanical engineer that a dimension of 1.000 mm was wrong.  I couldn't get him to understand that the default tolerance was +/- 0.0005 mm ! and the proper dimension should have been 1 mm, since it was not a critical part.  This engineer also dimensioned a 14 foot long square tube frame as 168.000 inches !

TJ McDermott
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Blogger
Re: default tolerances
TJ McDermott   1/20/2013 3:18:27 PM
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Your engineer didn't change the default tolerance in his CAD software.

This sin is most common coming from electrical engineers who don't normally design the mechanical side of things.

To their credit, electrical engineers have to deal with mechanical types not understanding PNP/NPN circuitry when it comes to sensors.

GlennA
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Gold
Re: default tolerances
GlennA   1/20/2013 8:33:31 PM
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T J McDermott;  CAD is a tool for a draftsman (or draughtsman) to create a drawing.  Computer hackers create garbage.  In my AutoCAD course I was taught what the most frequent mistakes made in CAD were.  On my first job in CAD, they were all there.  The most common mistake = all drawinga are drawn full size, but they are scaled to fit the paper size to be printed on.  The first drawing that I worked on would have needed a 300 ft sheet of paper.

And mechanical engineers (in my experience) do not understand that emergency stop and end-of-travel sensors are normally closed circuits.

Greg M. Jung
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Platinum
Re: Great article
Greg M. Jung   1/20/2013 10:34:33 PM
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Charles, I completely agree with you.  I'm mentoring and managing several young engineers now and unfortunately they were not taught basic tolerance capabilities for each manufacturing process.  I also agree that these basic manufacturing tolerances should be taught in all engineering colleges.

Dave Wittenberg Mcloone
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Iron
Re: Great article
Dave Wittenberg Mcloone   1/21/2013 3:35:14 PM
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Thanks for your post Charles!  We have 4 colleges/universities in the immediate La Crosse, Wisconsin area.  While we are actively involved with these institutions through internships and other programs we have not considered a manufacturing focused engineering lecture series.  Great idea...thank you for your suggestion.

Scott Orlosky
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Platinum
Re: Great article
Scott Orlosky   1/27/2013 12:03:05 AM
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I have to say Amen, Greg.  Improper tolerancing is expensive and too few mechanical engineers really learn that in school.  Unfortunately, often the young engineer learns tolerancing by doing it incorrectly.

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