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Keith Kokal


Extended Calibration Cycles May Cost More Than You Think

Instead, follow some preventive steps.

Published: Thursday, April 15, 2010 - 09:01

The collapse of the global economy has put a lot of manufacturing companies out of business. Even at this late stage of the recession, there are still auctions of recently closed plants conducted every day. There are many more manufacturers struggling to reduce their operating costs and improve their profitability just to remain in business.

One area in which companies are cutting costs is the calibration of their inspection equipment. I see this happening way too often without logical planning. At first glance, it seems like a good idea, but making rules across the board without analyzing the potential risks is further hurting companies. I recently received a phone call from a customer that rejected $7,000 in parts because their supplier extended the calibration cycle of their thread gauges. My customer needs these parts to complete their assemblies and ship completed expensive products. Their customer is demanding that their product keeps shipping. But even after an expensive sorting operation, the parts wouldn’t fit together. Now there are at least two companies in trouble due to the lack of reliable thread gauges. As a third-party independent calibration laboratory, we deal with the fallout of manufacturers using worn-out gauges. The scenario described above is just one of many we see and hear.

We try to help our customers save money and approach their cost-savings challenges while managing their risk. All of us performing calibrations and third-party inspections want our customers to succeed; it helps assure our future business as well. And it’s not a prudent business decision to simply skip calibrations or double the previous calibration cycles. Consider some of the following cost-saving options instead:

Identify gauges no longer being used. With the slowdown in production, you may have gauges for jobs you no longer make. Look at how many back up gauges you have and determine whether you still need them. Put the gauges not needed for current production in a controlled (limited access) area and let them set until needed again. However, keep enough gauges to cover production while your other gauges are being calibrated, or if one of them gets damaged.

Perform preventative maintenance on your gauges. For example, check your gauge blocks for magnetism. We routinely find gauge blocks that have become magnetic, probably from being used with magnetic parts or magnetic chucks and sine plates. These blocks have fine particles of iron attached to them and when they are wrung together, you are actually lapping the blocks and wearing them down. This same condition happens to thread gauges. You can do a simple magnetism check buy putting two paper clips together and sliding the hanging paper clip next to suspect gauges. Keep the lid on gauge block cases closed when not in use

Keep gauges clean. Gauges will last longer when kept clean and in good condition. Apply light oil to contact surfaces, especially in high humidity environments.

Micrometers. Check for lose ratchets near the end of the thimble. When these come loose, the barrel could slip (rotate) causing the micrometer to read incorrectly. Verify that the thimble rotates smoothly and make sure it feels in solid contact with the threads in the frame of the micrometer. If the threads feel loose there is an adjustment inside the micrometer to correct this problem. Clean and oil as necessary.

Indicators. Check for loose tips and use magnification while inspecting the tips for wear. It is common to find worn indicator tips. Verify that all of the screws on indicators are tight. When working with test indicators, make sure the proper tip is installed. End-users of these indicators do change the length of the indicator tip without realizing that this changes the magnification of the indicator. Make sure dust caps, bezel, and covers are in place and in good shape. This will help keep coolants and contaminants out and extend the life of the indicator.

Calipers. Verify the gib is not loose, as this could contribute to errors in values. Slide the jaws closed and hold the calipers near a light to see if excessive light comes through. If the jaws are nicked or damaged they may not close completely which would cause the zero setting to be wrong. Clean the rack and depth rod to help keep the caliper operating smoothly.

Adjustable torque wrenches. They should not be used at the same setting for their entire life. Torque wrenches should be moved around to different areas and used at different settings, which would allow varying components to share the wear. Because torque wrenches wear out, using them throughout their working range will extend their useful life.

Go/no-go plug gauges. Keep clean and oiled, check for magnetism and demagnetize as necessary. Remind end-users that these aren’t intended to be used to remove burrs, but they do it quite well in some applications. Many go/no-go gauges can be reversed inside the handle; this essentially gives you a new gauge, unless previously reversed.

These steps are normally inspected and corrected during routine calibrations and are good to follow as standard practice. Following them will increase the life of your equipment, improve equipment reliability, and save you money. When the economy improves, you will have reliable well-maintained equipment and will be ready for increased business.


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Keith Kokal