Other Dimensions: Making Your Mark
February 22, 2008
One of the essential elements in any quality program is identification of all the measuring instruments and gages that are part of it. Simply speaking, each should have a unique number for control and tracking purposes. Marking that number on equipment can be as simple as attaching labels or tags or engraving it directly on the item.
Use a temporary label for new tools entering the system, followed by a permanent label or engraved marking on the item. The temporary label is critical even though it may only be some masking tape with the number on it. What makes it critical is that it should be used until the gage or instrument in question has been calibrated and found to be satisfactory for your requirements. Then you can mark it in a permanent way.
If you put a permanent mark on a new tool then discover problems with it, it is unlikely your supplier will take it back for credit or exchange. Or you’ll have to pay a hefty restocking fee to cover the cost of getting rid of the marking. And if the marking was done incorrectly, the chances of it being returnable on any basis are virtually zero.
We frequently encounter instruments and gages that malfunction or are damaged because the wrong method was used for the marking or it was done in the wrong place on the item. The use of metal stamps is one culprit that causes untold damage to equipment even though the mark is permanent.
The best option is an electric pencil or handheld engraving tool, but these devices are not free of risks either. Because some of them rely on current flowing through the gage or instrument, if they are used to mark areas near encoder scales or the reading head portion of an instrument, they could damage the electronics or their programming.
Electrochemical marking as seen on many cutting tools is the least invasive and can be used on hardened steels. This system uses a stencil and electrolyte and an electric current so it is wise to keep such marks as far away from electronics as possible.
When it comes to go/no-go gages, their handles are easily marked by a number of methods. But some companies want the gage members marked as well, which is understandable since they may become detached from their handle or not have one at all. This is not a problem for large gages where the end face of the member can be marked. When small sizes are involved there won’t be enough room to do so.
Gage blocks should be left unmarked by their end user because damage or instability is sure to result from most marking methods. If the blocks are serialized or set numbered on each piece, these numbers can be used, but are rarely checked to ensure they match the calibration report. If you have to prevent pieces from one set getting mixed up with another, the simplest way to do so is to put a dab of paint on the non-precision surface of the block with a different color for each set. You can do the same thing with nail polish. You don’t have to study numbers to see if you’ve got rogue blocks in the set-a quick scan will show any pieces that don’t belong. The same method can be used for those low-cost pin gage sets.
If you use color coding as noted here or for other items in the system, make sure their calibration reports refer to the color code of the items. If you don’t do this, a quality auditor will want to know how you can tie a calibration report to a specific item.
Remember there is more to marking tools than identifying which company or department owns them. The marks must be legible as well as permanent. That means branding them like cattle won’t work very well. Besides, you’ll get all kinds of flak when you start building a fire to heat up the branding irons. At a more modern level, bar coding is another option assuming the bars don’t bring back painful memories for some staff members.
Editor’s Note: In Hill’s December 2007 column, the sentence reading “...the company that made the gage” should have read “the person that made the gage.”