WINTER 2014

192 THE DISTRIBUTOR’S

192 THE DISTRIBUTOR’S LINK MEASURING THE ANGLE OF A BEVELED RETAINING RING continued from page 46 What contributes to inaccurate measurement techniques is the very nature of metal stamping. Technical drawings of stamped parts depict straight lines and perfect angles. But the process of stamping a retaining ring yields a very different part as explained in the following diagrams. Above Left: The horizontal line has been set to 15 o . The bevel on the part is than aligned. Above Right: The horizontal line has been rotated back to 0 o . The image shows the position of the bottom using the bevel angle as the datum. The alignment is good but the bottom is not exactly flat. Above Left: Punch engages metal surface of strip steel. Forces create a radius edge at the top of the material. (This radius depends on the hardness of the material as well as the sharpness of the punch and die members). Above Right: As punch moves further through the material it shears and creates a straight, burnished wall from a quarter to a third of the way through. (This occurs when the die is properly sharpened and when the correct clearance has been applied). Above: Forces build up to a point where the material shears and breaks away. This is called the “breakoff” which features a rough surface that tapers back somewhat. Burrs can also occur at this point in the stamping process. The characteristics of metal stamping thus complicate efforts to conduct measurements on the actual part, including the angle of the beveled retaining ring. For example, one common method of measuring a beveled ring is to use a comparator, as per below: Above: The horizontal line has been rotated back to 0 o . The image shows the position of the top using the bevel angle as the datum. The alignment is good but the top is not exactly flat Using either the bevel angle or the bottom of the ring as the datum point will not yield accurate results due to the characteristics of stamping discussed above. Also, this method is visual and does not involve actual contact points on the ring, which can further render it unreliable. The method that delivers the highest degree of accuracy is a contracer which measures the two critical dimensions of the angle and the bevel thickness. (Note: measuring only the bevel angled and not using the bottom of the ring as a reference point will render an inaccurate reading). The contracer can measure both of these accurately using a dual stylus. This measures the angle of the bevel, then the thickness from the bottom of the ring. After programming the machine for the size of ring to be measured, the stylus moves along the top of the ring taking data points as it progresses. As noted previously, the stamping process does not result in perfectly straight cuts so these measurements will vary slightly as the stylus moves along the surface of the ring. please turn to page 193

THE DISTRIBUTOR’S LINK 193 MEASURING THE ANGLE OF A BEVELED RETAINING RING continued from page 192 The stylus then shifts and travels along the bottom of the ring measuring data points along the irregular surface and recording the results as it progresses. At the completion of the program a printed profile is generated from the highest two points at the top of the ring and the lowest two points at the bottom (this portion is critical since it engages the retained part). The program will then show the exact dimensions and whether or not they conform to specs. The use of the dual stylus technique is critical in obtaining accurate measurements. Some contracers use a single stylus. In order to measure both the top and bottom, the ring has to be removed from the holder and flipped, which will disturb the alignment and produce an invalid reading. The methods of producing beveled rings and the method of measurements can vary as noted. However, use of the dual stylus contracer has proven itself to be a valuable tool in yielding accurate results that can attest to the proper functioning of the part in application. Above: A dual stylus ensures accuracy by measuring the top and bottom of the ring without having to re-position it as required if using a single stylus. Below: The program produces a profile showing the angle measurement and the thickness of the ring.