CALLIPER ROD FOR MEASUREMENT OF VERY SMALL DISTANCES, METHOD FOR MEASURING THE DISTANCE BETWEEN THE ELECTRODES OF A SPARK PLUG USING THE SAID ROD AND PROCESS AND TOOL FOR MAKING THE SAME

摘要

The invention relates to a calliper rod intended to measure very small distances, such as the distance between the electrodes of a spark plug, to a method for measuring the distance between the said electrodes and to a process and a tool for carrying out the rod. According to the invention, the rod (tm) has 16 or 20 progressively increasing thickness steps (t) exhibiting an increment of 0.1 mm as compared with the previous step from the tip, where the thickness has the minimal value of 0.1 mm towards the base where the thickness has the maximal value of 1.6 mm, 2.0 mm or 2.54 mm, the rod (tm) having a length of 8 or 10 mm, a width of 3...4 mm, a stiffening and guiding rail (s) and an orifice (o) enabling it to be attached to a calliper slide. The claimed method of measurement consists in using a calliper provided with a rod (tm) sliding between the electrodes of a spark plug until the distance between the electrodes reaches the step (t) of the rod (tm) having the same thickness, the value of the distance between the electrodes being then read on the calliper slide. The process, as claimed by the invention, starts by cutting the raw material, which is a 175 mm-long, 9 mm-wide and 1.6 mm-, 2.0 mm- or 2.54 mm-high parallelepipedal rectangular rod, on a half of its width, resulting into two 4 mm-wide mirroring rods, the two halves of the fastening and machining tool are spaced apart by sliding along the alignment cylinders (7) in order to allow the rod to enter the cavity (2) to be fastened, the two halves being then moved closer to each other in order to prevent the rod displacement, two holes are drilled at the rod base, using a drill of a diameter of 2 mm which enters the cylindrical cavities (4) to form the recesses for anchoring the rod, by riveting, to the rod slide, after which the steps are formed by milling with a computerized 7 mm-wide milling cutter which penetrates step by step, at an increment of 0.1 mm throughout the length of 150 mm and the rod (tm) is cut lengthwise in its medial region, starting from its tip.