【For guides of different shapes, which plane straightness errors should be controlled for each surface?】
Answer: The common shapes of machine tool guide rails are rectangular guide rails and V-shaped guide rails. The horizontal surface of the rectangular guide rail controls the straightness error of the guide rail in the vertical plane. The two sides of the rectangular guide rail control the straightness error of the guide rail in the horizontal plane. For V-shaped guide rail, because the guide rail is composed of two inclined surfaces, the two inclined surfaces control the straightness error in both the vertical plane and the horizontal plane.
【What are the common detection methods for straightness error of guide rail?】
Answer: Common detection methods for straightness error of guide rail include: grinding point method, flat ruler pull meter comparison method, pad plug method, pull wire detection method, level meter detection method, optical collimator (autocollimator) detection method, etc.
【What is the point study method?】
Answer: When measuring the straightness error of the guide rail with a flat ruler, evenly apply a thin layer of red lead oil on the surface of the guide rail to be inspected, put the flat ruler back on the surface of the guide rail to be inspected, use appropriate pressure to make a short reciprocating movement for lapping, and then take down the flat ruler to observe the distribution of lapping points on the surface of the guide rail to be inspected and the density of the thinnest part of the lapping points. If the grinding points are evenly distributed over the entire length of the guide rail, it means that the straightness error of the guide rail has met the corresponding accuracy requirements of the ruler. This method is called point grinding method.
The flat ruler used in the lapping method is a standard flat ruler, and its accuracy grade is selected according to the accuracy requirements of the inspected guide rail, which is generally not lower than grade 6. The length shall not be shorter than the length of the guide rail to be tested (the length of the ruler can be 1/4 shorter than the guide rail in case of low accuracy requirements).
【Which types of guideway straightness error is the grinding point method applicable to?】
Answer: When the straightness error of the guide rail is trimmed by scraping, the lapping point method is mostly used. The lapping point method is often used for the detection of shorter guide rails, because the ruler is easy to deform when it exceeds 2000mm, making it difficult, and affecting the measurement accuracy. When scraping short guide rails, the straightness error of the guide rail is usually guaranteed by the accuracy of the flat rule. At the same time, there are certain requirements for the density of the grinding points in the unit area. According to the accuracy requirements of the machine tool and the nature and importance of the guide rail in the machine tool, it can be specified as every 25mm × The number of grinding points within 25mm shall not be less than 10-20 (i.e., the number of points within each scraping square).
When the grinding point method is used to detect the straightness error of the guide rail, because it cannot measure the error value of the straightness of the guide rail, when there is a level, the grinding point method is generally not used for the final detection. However, it should be pointed out that in the absence of measuring instruments (level meter, optical straightness meter, etc.), the inspection ruler produced by the mutual research method of three rulers can effectively meet the detection requirements for straightness error of short guide rails of general machine tools.
【The straightness error of which planes of the guide rail can be measured by the comparison method of level ruler and pull meter?】
Answer: The straightness error of the short guide rail in the vertical plane and the horizontal plane is usually detected by the comparison method with a ruler and a dial gauge. In order to improve the stability of the measurement reading, the length of the sizing block moving on the inspected guide rail generally does not exceed 200mm, and the contact surface between the sizing block and the guide rail should be scraped with the inspected guide rail to ensure good contact, otherwise the accuracy of the measurement will be affected.
(1) Detection method of straightness error in vertical plane. Place the working face of the ruler horizontally beside the guide rail to be tested, and the closer the distance is, the better to reduce the influence of the guide rail distortion on the measurement accuracy. Place a sizing block on the guide rail that is scraped with the guide rail, fix the dial indicator base on the sizing block, make the dial indicator measuring head focus on the surface of both ends of the ruler successively, adjust the flat ruler to make the readings of the dial indicator on the surface of both ends of the ruler equal, then move the sizing block, read the dial indicator value every 200mm, and the maximum difference between the readings of the dial indicator is the straightness error within the full length of the guide rail. During measurement, in order to avoid the influence of scraping point and make the reading accurate, it is better to place a measuring block under the dial indicator probe.
(2) Detection method of straightness error in horizontal plane. Place the working face side of the ruler beside the guide rail to be tested, and adjust the ruler to make the readings on the two ends of the ruler of the dry sub meter equal. The measurement method and calculation error method are the same as above.
【Which guide rails are suitable for straightness error detection by the plug method?】
Answer: The cushion plug method is applicable to the inspection of ground and low surface roughness plane guide rails. On the inspected plane guide rails, place a standard ruler. At the distance of 2/9 • L from both ends of the ruler, use two equal height cushion blocks to support under the ruler. Use a gauge block and a feeler gauge to check the gap between the working surface of the ruler and the measured guide rail surface. If the straightness tolerance of the guide rail of the horizontal lathe is (1000:0.02) mm, that is, use a gauge block or feeler gauge equal to the thickness of the equal height cushion block plus 0.02mm, and it is qualified if it cannot be inserted anywhere within the 1000mm length of the guide rail. When measuring the guide rail of precision machine tool, it is advisable to use a gauge block with high accuracy, so that the straightness error value of the guide rail can be measured correctly. In this method, a dial indicator can also be used to replace the feeler gauge, but the thickness of the constant height cushion block shall be increased so that the dial indicator can enter the measurement.
【What are the characteristics of measuring the straightness error of the guide rail with the wire pulling inspection method? What should be paid attention to during operation?】
Answer: Take the tensioned steel wire as the ideal straight line, and directly measure the straightness error line value of each component surface on the guide rail. It is a linear measurement method, just like the comparison method with a ruler.
This method can only detect the straightness error of the guide rail in the horizontal plane. Place a 500 mm sizing block on the guide rail of the bed, and install a reading microscope with a scale on the sizing block. The lens of the microscope should be aligned with the steel wire and must be placed vertically. At both ends of the guide rail, a small pulley is fixed with a steel wire with a diameter less than 0.3mm. One end is fixed on the small pulley, and the other end is suspended with a heavy hammer. The weight of the heavy hammer shall be 30%~80% of the breaking force of the steel wire. Then adjust both ends of the steel wire so that when the microscope is at both ends of the guide rail, the steel wire coincides with the scribe line on the lens. Record the reading on the hand wheel of the movable reticle on the microscope.
Move the sizing block and observe the microscope every 500mm to check whether the steel wire coincides with the scribed line. If not, adjust the hand wheel on the reading microscope to make it coincide, and record the reading. Measure the total length of the guide rail and record the readings in sequence. Arrange the readings on the coordinate paper and draw the movement curve of the sizing block. The maximum coordinate difference between the motion curve and the connecting line at both ends of the point on each 1000mm length is the straightness error on 1000mm length. If the curve formed is a convex or concave line, the coordinate difference between the most convex or concave point and the two ends of the connection is