1. Perpendicularity of the side of the straightedge against the working surface: Place a granite straightedge on a flat plate. Pass the dial gauge, equipped with a 0.001mm scale, through a standard round bar and zero it on a standard square. Then, similarly, place the dial gauge against one side of the straightedge. The dial gauge reading is the perpendicularity error for that side. Similarly, test the perpendicularity error for the other side, and take the maximum error.
2. Contact Point Area Ratio of Parallel Straightedge: Apply a display agent to the working surface of the straightedge to be tested. Grind the surface onto a cast iron plate or straightedge of at least the same accuracy to reveal distinct contact points on the working surface. Then, place a transparent sheet (such as a plexiglass sheet) with 200 small squares of 2.5mm x 2.5mm, measuring 50mm x 25mm, at any position on the working surface of the straightedge to be tested. Observe the ratio of the area of each square containing the contact points (in units of 1/10). Calculate the sum of the above ratios and divide by 2 to obtain the ratio of the contact point area of the tested area.
Third, support the parallel ruler with equal-height blocks at standard support marks 2L/9 from each end of the ruler. Select an appropriate testing bridge based on the length of the ruler’s working surface (generally 8 to 10 steps, with a span between 50 and 500mm). Then, place the bridge at one end of the ruler and secure the reflector or level to it. Move the bridge gradually from one end of the ruler to the other, moving each span from an autocollimator with a graduation of 1″ (or 0.005mm/m) or an electronic level with a graduation of 0.001mm/m (for a working surface length greater than 500mm, a Class 1 ruler with a graduation of 0. The reading at this position can be taken with a 0.01mm/m coincident level (a frame-type level with a graduation of 0.02mm/m can be used for a level 2). The difference between the maximum and minimum readings is the straightness error of the level’s working surface. For any 200mm of the working surface, the straightness error can be determined using a 50mm or 100mm bridge plate, using the above method.
IV. Parallelism of the upper and lower working surfaces, and of the working surface and lower support surface, of a parallel level. If a suitable flat plate is not available, the side of the level can be placed on a support surface and the height difference of the level measured using a lever micrometer with a graduation of 0.002mm or a micrometer with a graduation of 0.002mm.
Post time: Sep-04-2025