Evaluating Gaging For The Shop Floor
Measuring instruments have been used for the inspection of manufactured parts ever since the first vernier caliper was introduced. It wasn't difficult to take care of those old tools on the shop floor: A clean cloth, a little elbow grease and a good storage box were all that was needed to make those gages last a lifetime.
Director of Precision Gages, Mahr Federal Inc.
Measuring instruments have been used for the inspection of manufactured parts ever since the first vernier caliper was introduced. It wasn't difficult to take care of those old tools on the shop floor: A clean cloth, a little elbow grease and a good storage box were all that was needed to make those gages last a lifetime. In fact, they often became prized possessions, as craftsmen handed down tools from generation to generation.
In the past 30 years or so, electronic gages have become increasingly common on the shop floor because of their ease of use, speed and ability to do complex measurements. However, when it came to caring for these new gages, one thing was clear: You didn’t want to get that digital caliper, micrometer, indicator, amplifier or computer anywhere near water or coolant, or there was sure to be trouble. Either the gage wouldn’t work, or, even worse, it would produce incorrect readings.
It didn’t make sense that these gages didn’t operate properly in an environment where coolant, grease, dirt and chips were among the normal working conditions.
Recently, there have been improvements in many of the electronic gaging tools that finally give them the characteristics needed to survive on the shop floor. Improvements in scale technology, microcircuits and sealing have made gages capable of literally taking measurements under water.
Now that these types of gages are finally available, a new standard has been created to help identify what type of tool is best for the environment in which it will be used. This rating is called ingress protection (IP). Associated with the IP is a two-digit rating number that tells what type of conditions the gage can survive in. The first digit describes the protection for solid foreign objects, while the second digit indicates protection against harmful ingress of water. A potential third digit, which is the defined impact protection, has not yet made its way into the measuring instrument table (see chart).
For example, a gage might have a rating of IP-65. As you can see from the accompanying table, this gage is totally protected against dust and low pressure jets of water from all directions, with limited ingress permitted. Today there are calipers and micrometers with ratings as high as IP-67. These can be subjected to the type of dust and dirt found in the shop, and they are both coolant proof and waterproof.
So, electronic tools can finally be used on the shop floor. What a good idea! But one cautionary note: Just because these new gages can handle the environment doesn’t mean that their measurements are impervious to environmental conditions. They are still precision gages, and all the basic rules for precision gaging still apply. We’ll review the classic SWIPE paradigm next month.
|First number (Protection against solid objects)||Definition||Second number (Protection against liquids)||Definition|
|0||No protection||0||No protection|
|1||Protected against solid objects over 50 mm (for example, accidental touch by hands).||1||Protected against vertically falling drops f water.|
|3||Protected against solid objects over 12 mm (for example, fingers).||3||Protected against direct sprays up to 15 degrees from the vertical.|
|4||Protected against solid objects over 2.5 mm (for example, tools and wires).||4||Protected against direct sprays up to 60 degrees from the vertical.|
|5||Protected against dust. Limited ingress (no harmful deposit).||5||Protected against low pressure jets of water (for example, for use on ship decks.). Limited ingress permitted.|
|6||Totally protected against dust.||6||Protected against strong jets of water (for example, for use on ship decks.). Limited ingress permitted.|
|7||Protected against the affects of temporary immersion between 15 cm and 1 m. Duration of test is 30 minutes.|
|8||Protected against long periods of immersion under pressure.|