AGD Versus DIN Style
Use this as a primer in master ring philosophy.
In today’s manufacturing environment, most people are comfortable working to the industrial standards that apply to their region. In the United States, the standards might originate from any one of several groups with acronym names such as ANSI, ASME, AGMA or others, depending on what products are being manufactured.
However, if a company wants to be a player in the global market, it must be familiar with—and potentially use and manufacture products to—standards from other regions and countries. It’s not uncommon for each country to have its own standards and thus demand slight differences in products or features. For example, one would have to know DIN and ISO standards for Europe, JIS standards for Japan, and SAC for China.
We manufacturer and inspect precision rings for the U.S. to the ASME B47.1 standard that defines the gage blanks and then to ASME B89.1.6 for final inspection and classification. A master ring, or ring gage, is basically a bore of known dimension used as a setting master for variable inside-diameter gages such as bore gages, air tooling and mechanical plug gages. The ASME standards define the rings in classes, with XXX indicating the tightest tolerances; XX, X and Y denoting intermediate grades; and Z the lowest. Class tolerances vary by size; larger sizes have more open tolerances since they are harder to manufacture.
For example, the following tolerances would apply for a 0.820-inch master ring:
Class XXX = 0.00001 inch
Class XX = 0.00002 inch
Class X = 0.00004 inch
Class Y = 0.00007 inch
Class Z = 0.00010 inch
Of course, the better the class, the more expensive. The XXX ring is manufactured to a tighter tolerance, and there is cost involved with this. It may take longer to manufacture, take the skill of a more highly paid technician or, if something goes wrong, it may have to be remanufactured and take longer to deliver.
This class philosophy comes from the way we tend to master our gages here in the U.S. The idea is to make a master as close to the nominal size as possible and then set the gage display to read zero when the master is placed on the gage. But as noted, this can be a cause for added cost, longer delivery time and shorter master life when the highest grade of masters are specified.
In much of the rest of the world, DIN masters (or some derivation of these standards) have been adopted. DIN 250 A, B and C are pretty much used to manufacture and measure the precision rings. In both systems, a precision hole is bored in a piece of steel and precisely refined to a known size, form and surface finish. But in the DIN world, things are a bit different, both in terms of physical dimension and mastering philosophy. Let’s look at some of the small differences between an AGD and DIN Type B ring used for mastering air gaging.
As seen in Figure 1, for example, there is a slight difference in the physical size of the ring blanks or “hole holders” being used for the masters: