TRAINING TRENDS: Caring for your Surface Plates increase the life of surface plates.
Surface plates have many uses. A surface plate is the “0“ reference point. If a height gage is used on the plate, the operator must “0“ that gage anywhere on the plate with a gage block. Remove the gage block and check a part to see if it is flat. However, this is mostly for small parts in mass production. Most automotive manufacturers use the plate to check for warp age of a chassis or crankshaft, as does the aircraft industry and other industry sectors. The usage is unlimited. Not only are the plates used in final quality control inspections but also throughout an entire plant as parts are being manufactured. Regardless of what piece of equipment is used to perform the daily work, individual parts are checked in manufacturing, and the finished product was probably checked before the final inspectors put their stamp of approval on it.
After years of using a plate, a quick way to check to see that the plate is maintaining its accuracy is to periodically test it with a repeat reading gage with a manual indicator. With this equipment, all that is required is to set the gage on the plate and zero it at any point on the table. Simply move the gage over the plate and if there are hand movements in the indicator more than 0.000025 inches for an “AA“ plate, 0.00005 inches for an “A“ plate or 0.0001 inches for a “B“ grade plate, then there is an indication that the surface plate may have some high and low spots and be out of tolerance. The tolerance must repeat from side to side within the specified tolerance range to be a good plate. If the plate proves to be out of the tolerance range there are relapping service companies throughout the United States that offer a calibration and relapping service in the customer's facility. A plate should be calibrated on an established cycle, typically one, two or three years depending on use.