Archive for September, 2009

This week’s tip: Temperature-sensitive tools

Posted in Uncategorized on September 29, 2009 by Peter

Jerry likes to tell the story of a shop boss who brought a newly-calibrated micrometer back to the mobile lab.  The machinist using the mic claimed it was off by several tenths (tenth = .0001″).  That’s a significant error because mics are only allowed a one-tenth deviation, plus or minus.

Jerry let the tool sit for a while so it would be the correct temperature; then he checked it again, and it was right on the money.  A brief inquiry of the machinist followed.  Sure enough, he’d been holding the mic in his bare hands.  That warmed it up to nearly 100 degrees, expanding the frame and yielding undersized readings.

So this week’s tip is simple:  If you must hold a micrometer, hold it with something to insulate it against your body heat.  A rag is fine, for instance.  Many mics are now made with plastic insulators attached (such as the one pictured at the top of this page), so there’s less chance of heat expansion.  However, always be aware of how you’re handling your tools.

Next time:  Size matters; also, other tools’ heat sensitivity

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This week’s tip: Control your temperature

Posted in Uncategorized on September 17, 2009 by Peter

Mobile Precision’s ad copy about a “climate-controlled mobile lab” sounds like boasting, but it’s not.  Climate control, especially temperature, is a vital facet of tool calibration.   All national and international standards of measurement are specified under exacting environmental conditions.  For our purposes, we operate in temperatures from 68 to 73 degrees Fahrenheit, and 38 to 58 percent relative humidity.  This keeps us in compliance with NIST, and gives the end-user a benchmark for standards and quality.

We’ll deal with specific tools and conditions next time.  For now, keep in mind that nearly every tool you use to check dimensions has at least some metal components, and that metal responds to temperature changes by expanding or contracting.  These changes can be significant and even critical, and they affect how your tool acts.

Next time:  What tools are most sensitive to temperature?