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Is It More Powerful Than A Machine? Share A Little Knowledge About Machine Tool Scraping (2)

May 13, 2019

Previously, ALLES CNC shared the technology of “precision machine tool scraping”. Now, ALLES CNC will bring you more in-depth understanding of how to carry out the “scraping” precision machining.

Scraping steps

Machine tool scraping is not a simple technique. The senior technical engineer of ALLES CNC said that the research must be carried out through numerous exercises into spontaneous movements. Thousands of repetitive fine-tuning postures are performed every day to gain control of the waist. The length and width, the left hand pressure channel determines the depth, the right hand controls the scraping point, and the center of gravity of the feet fits into a smoother body memory. Although it is a simple and easy job, after careful analysis, it is not difficult to find that it has certain technical characteristics.

Be aware that the difference between the highest and lowest rails of the machine may be very small 0.01mm or 1mm, which is uneven. That is to say, if the same force is used for scraping, there will be no smooth surface at all, so the scraping will require the strength of each knife to be different. Similarly, scraping is not like ordinary art sculptures. As long as one place is not allowed, it will affect the precision of other places. Plus more than one plane, and four or more must be shovel accurate at the same time, more than one surface difficulty is not addition, but multiplication, shovel can only be dug, can not make up, once shovel the wrong place to start again, Others are equal to white, this is its difficulty.

Scraping classification

It should be noted that although the machine tool scraping is classified as “finishing”, the scraping is also classified internally. According to the different properties of the products produced by each mechanical device and the different ways of use, the scraping is also divided into rough scraping and fine grinding. Scrape, fine scrape, and scrape four parts.

Rough scraping: If the surface of the workpiece is rough, the processing marks are deep or the surface is severely rusted, uneven or distorted, and the scraping allowance is above 0.005mm, it should be rough scraped first. The rough scraping feature is a long scraper with a long stroke (between 10mm and 15mm) and a wide knife mark (10mm). The scraper traces are smooth and the sheets are not repeated. After the machined tool marks are scraped off, the points can be ground and scraped at the high points shown. When the surface of the workpiece is 4 to 6 points per 25 mm × 25 mm, the rough surface is stopped when the surface roughness is (Ra2.5-Ra3.2).

 Fine scraping: Fine scraping is to scrape off the high point after rough scraping. It is characterized by short scraping method (knife mark width is about 6-8mm, length 10-12mm), and the grinding point is dispersed quickly. When scraping finely, it is necessary to scrape in a certain direction, and scrape it again. When scraping the second pass, it is necessary to cross the web in a direction of 45 degrees or 60 degrees. When the average grinding point is 10 to 14 points per 25 mm × 25 mm, the flatness is 0.01 mm / 500 mm 2 , and the surface roughness (Ra 1.6 - Ra 3.2) should take into account the shape difference, the fine scraping can be ended.

 Fine scraping: fine scraping on the basis of fine scraping, using small scraper or fine scraper with arc, the knife mark width is about 5-7mm, or shorter. The average grind point should be 20~25 per 25mm×25mm. When the flatness is 0.01 mm/500 mm 2 or less and the surface roughness is Ra 0.8-Ra 1.6, the fine scraping is finished. Commonly used for inspection of tool, precision rail and close tool contact surfaces.

 Scratch: The effect of scratching is aesthetics, and the second is the function of accumulating lubricating oil. Common patterns include: diagonal patterns, swallow patterns, and fish scales. In addition, the degree of wear after the plane work can also be judged by observing the integrity and disappearance of the original pattern.


If you still have some doubts about the technology of machine tool scraping, ALLES CNC has collected the understanding of other people in the industry about scraping.


The shovel scraping is not as magical or mysterious as the legend. The shovel scraping itself does not have such high precision, but it subtly corrects the part error to zero, and distributes the large processing error evenly over a certain area. It is not flat, but from the perspective of the entire contact surface, it is flat. Because the machine tool error must not be completely eliminated, if it is simply to improve the accuracy of the machine tool, then the cost may increase geometrically, so scraping is an economical good way. Also, the scraper does not cause thermal deformation.


The technique is called "scraping" and "shovel" in the fitter textbook is just the last process of scraping. Scraping is a common method used by mechanics, and it is divided into scraping and grinding. Scrape and use the scraper to make a scraping motion on the metal surface lower than the hardness of the scraper, and go high and low. Grinding is performed by applying a coloring agent to the surface of the workpiece to be scraped with a standard instrument (flat, bridge, and ruler). , showing a high point. Scraping the high point, going back and forth, can be completed after a long process. The test standard is 25 square millimeters of displayed ideas, 25 ideas are already very high, generally not so high. The shovel is only to scrape the regular pattern on the surface of the workpiece that meets the requirements. On the one hand, for the sake of beauty, on the other hand, in order to improve the movement conditions, the two movements are prevented from being absorbed. Scraping is a very heavy manual labor. Modern machine tool guides are ground out after quenching. But this technology is still indispensable in machine tool repair.


In the process of forging casting, the metal material will be deformed by the internal stress of the material. The accuracy of the machine tool will only affect the size of the deformation, but it cannot be completely eliminated. Therefore, it is necessary to use the scraping process in a non-stress environment. This deformation error is further reduced or eliminated to achieve the accuracy required for surface contact mating. In addition, it can be used on the rails of hard-rail machine tools to form oil pool effect, reduce friction and improve the service life of the track. There are also different scratch-off criteria in different usage environments, but all are in percentage contact points per square centimeter.


Most of us are women to scrape, I heard that the labor department is not allowed to do this profession, the intensity. But listening to the women workers, a lot of men shaved no women, often scraped, especially fine and pick flowers! Repair the platform, please come to the factory, the technical supervision bureau acceptance!


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