Part 1: Plain Plug Gages

This is not a how-to column but rather an overview of what is required in the way of hardware used for gage calibration. As with any measuring process, several types of equipment can be used; I will only deal with the most commonly used equipment. It is assumed that you have a proper environment, your equipment and masters are calibrated, and you have a skilled person to use the equipment.

The original intent of certificates of compliance was to make sure that process steps were not overlooked if they could not be verified later. An example of this might be a product that has to be dipped in a specified solution at a specified temperature for a specified period of time before painting or plating. Usually, there is no way to verify that these steps were taken once the product has been coated. Testing after-the-fact can reveal that the correct thickness of paint or plating has been applied but not that all specified process steps were followed.

The problem starts with buyers of special rings who do not wish to pay for proper setting plugs. When it’s time for calibration, the hunt begins for someone who has plugs and of course, it’s unlikely they will be found because calibration laboratories would go broke keeping special setting plugs on hand in most cases. Some laboratories are ready to cash in on this situation by offering to “measure” special adjustable thread ring gages so the technician won’t have to buy the right thing. And, wow, the cost will be a lot cheaper than buying setting plugs.

Acceptance criteria, like purchasing criteria, begin with workpiece tolerance.