- THE MAGAZINE
- WEB EXCLUSIVES
Editor's note: This installment in a multipart series focuses on manufacturers doing their own calibration. The series looks at the reasons why a manufacturer might make this choice, as well as some of the considerations that must be taken into account when embarking on this course of action.
Most manufacturers assume they'll be able to use existing staff when they make the decision to bring calibration in-house. Besides the costs associated with such a decision, skills and knowledge of the people doing the calibration are important as well.
Many companies produce components that have accuracy requirements similar to gages. Operators working in such an inspection department can adapt to calibration work because there are usually stringent quality standards already in place, and these employees have an appreciation for close-tolerance metrology.
For most companies, the people who do a lot of the general inspection work are essentially instrument readers. They never received training in the basics of dimensional metrology so they are unaware that there is a difference between a reading and a measurement. In everyday work, this is not a big problem, but it does leave them at a disadvantage if they are expected to do calibration work. Step-by-step work instructions, in the form of calibration procedures, help, but there is no substitute for someone having the appropriate skills and knowledge.
Many people doing calibration work at the manufacturing level are essentially left to their own devices, literally. Often, management is more concerned that these individuals know how to enter data to a computer than how that data is obtained or what it represents.
If a manufacturing staff has the requisite skills to do the job, the next factor to keep in mind is that the measurement uncertainty associated with calibration is usually to a higher order than what is suitable for product measurements. It also is necessary to prove these in-house calibration people are up to the tasks of their position. The best way to ensure their ability is by testing them from time to time.
Most often the work of an in-house calibration staff will involve the wringing of gage blocks, so the staff should be tested to see how well they can repeat the "master" they create with the blocks. An easy way to accomplish this is by testing them to wring four blocks together. After the buildup has settled, use it to set a high-resolution comparator to zero. Use a marker to draw a line down one side of the buildup so it can be recreated without flatness and parallelism situations clouding wringing ability. Have the technician wring the stack again, let it cool and check it on the comparator. All other factors being equal, variations from zero indicate the fluctuation to be expected when that person wrings up blocks.
It is often instructive to have the same instrument or gage calibrated by several people that do calibration. This gives the manufacturer comparable results of calibration staff members' capabilities.
Calibration training may be available from equipment sellers. Similarly, community or technical colleges often offer courses to upgrade basic skill levels in calibration work.
Training also may be available from the lab that does a company's outsourced high-accuracy calibration work. If that outside lab knows they will not get a manufacturer's low-end calibration work, they may allow in-house calibration staff watch them do similar items. Expect to pay a fee for such training, as it does slow down the lab's scheduled work. But, the benefit of much experience can be gained from people who do calibration work on a volume basis. An outside lab will have seen most anything an in-house calibration staff will encounter.
Keeping a log of calibration training, whether provided internally or externally, is important. Keep records of any testing of an in-house calibration staff's skills. An independent assessor will want to verify training and testing records.
Now that the hardware, people and the place to do calibration are sorted out, it's time to examine "when" calibration is to be done. That will be the subject of next month's column.
Hill Cox is president of Frank J. Cox Sales Ltd. (Brampton, Ontario, Canada.) He may be reached at firstname.lastname@example.org.