The performance of any tool in terms of repeatability & accuracy mainly depends on the following factors :

• Tool Design
• Age of the tool
• Frequency of use
• Handling of the tool in the assembly line
• Periodic maintenance procedure being followed.

Disadvantages of fixed calendar (time) based calibration interval

1. Ignores differences between the age of different tools in the tool crib. A tool in use for 5 to 10 years gets lumped in with a tool which was purchased recently.
2. Ignores the difference between usage rates of different tools. A tool which is being used 3 times /minute gets lumped with the tool which gets used three times an hour.
3. A tool which is calibrated infrequently causes problems in the assembly process & results in cost in
   time, money & effort to look into the problems which may or may not find out the tool calibration
   interval is really the root of the problem.
4. A too frequent calibrated tool results in money , time & effort being wasted

Basic Idea

• If the torque wrench or power tool needed no adjustment on verification of calibration then the duration between calibration intervals can be extended.
• If the torque wrench or power tool needed adjustment on verification of calibration then the duration between calibration intervals should be shortened.
• The information on whether or not adjustment was needed is right on the calibration certificate & need only to be examined. Ideally , Certificate should comply with TS 16949 & ISO calibration requirements. (link to TTM software)

Acknowledgements – Excerpts from Sturtevant Richmont (Education)