The operation of scraping various patterns on the surface of a workpiece after fine shaving or fine shaving, finishing and grinding is called scraping, also known as embossing and picking. The scraping operation generally uses a fine scraper or a special knife for scraping.
There are many types of patterns. Here are some common patterns, such as curved patterns, square patterns, wavy patterns and scalloped patterns. The curved patterns mainly include moon patterns and swallow patterns.
1. Basic shaving method of curved pattern
First, use the scraper blade to drop the knife on the left side, then scrape it diagonally from left to right (as shown in Figure 1a), while the left wrist should twist the wrist to make the blade swing from left to right (Figure 1b) As shown in the figure, the scraping of the cutting edge portion is changed from the left side to the right side, and the longitudinal length of the cutting edge is generally about 10 mm, and the entire scraping process is completed instantaneously, so that various curved patterns can be scraped off. It can also be scraped obliquely from right to left. When the wrist is forced down by the left wrist, the right hand twists the wrist to make the blade swing from right to left, so that the scraping of the cutting edge transitions from the right side to the left side.
Curved pattern scraping method: Due to different shaving conditions and operation methods, the shape and arc angle of the scraped pattern are also quite changed. First, we must pay attention to the selection of a suitable scraper, because the width and thickness of the cutter head, the radius of the cutting edge and the size of the wedge angle have a certain influence on the shape of the curved pattern; the second is to be able to control the wrist movement during scraping. The amplitude and the length of the sliding stroke; the third is to use the elastic action of the cutter head. Generally speaking, the greater the amplitude of the twisting motion, the shorter the pushing stroke, and the smaller the angle of the curved pattern is. The smaller the shape, as shown in Figure 1c.
(1) Moon pattern and scraping method The moon pattern is shown in Figure 2.
Before scratching, use a pencil to draw a square of a certain distance on the surface of the workpiece.
When scraping, the arc-blade fine scraper is used, and the center line of the blade plane is at an angle of 45° to the longitudinal center line of the workpiece surface, and is scraped from the front to the back of the workpiece.
(2) Swallow pattern and scraping pattern The swallow pattern is shown in Figure 3a. Before scratching, use a pencil to draw a square of a certain distance on the surface of the workpiece. When scraping, the arc-blade fine scraper is used, and the center line of the blade plane is at an angle of 45° to the longitudinal center line of the workpiece surface, and is scraped from the front to the back of the workpiece. The common scraping method is:
First, the first knife scrapes a curved pattern, and then the second curved pattern is scraped off slightly below the first curved pattern, so that a pattern resembling a swallow can be scraped, as shown in Fig. 3b.
2. Square pattern and scraping method
The square pattern is shown in Figure 4. Before scratching, use a pencil to draw a square of a certain distance on the surface of the workpiece. When scratching, the center line of the blade plane is at an angle of 45° to the longitudinal centerline of the workpiece surface, and is scraped from the front to the back of the workpiece. The basic scraping method is: using a straight blade (or a large radius arc blade) narrow scraper for short-stroke scraping, after scraping the first square, it should be separated by a square distance and then the second square is scraped out.
3. Wave pattern
The wave pattern is shown in Figure 5a. Before scratching, use a pencil to draw a square of a certain distance on the surface of the workpiece. When scratching, the center line of the blade plane should be parallel to the longitudinal centerline of the workpiece surface and scraped from the back side of the workpiece. The basic scraping method is: scraping with a slit scraper, selecting the position of the falling knife (generally selecting the intersection point), and moving the scraping obliquely to the left side after the falling knife, when reaching a certain length (generally selecting the intersection point) is followed by The right side is tilted and pushed to a certain position to start the knife, as shown in Figure 5b.
4. Sector pattern
The scalloped pattern is shown in Figure 6a. Before scratching, draw a square and angle line with a pencil on the surface of the workpiece. To scrape the fan-shaped pattern, use a hook-and-blade scraper (as shown in Figure 6b). Sharpen the right end of the blade, make the left end slightly blunt, and the blade line should be straight. The basic scraping method is:
Select the position of the falling knife (generally choose the intersection point), hold the left hand at 50mm from the cutter head, press the left side down with force, with the left end of the blade as the center, and the right hand rotate clockwise. The rotation angle is generally 90° and 135°. . The correct fan-shaped pattern is shown in Fig. 6c. Due to improper force, it is easy to cause both ends to be scraped at the same time, forming a pattern as shown in Fig. 6d, so that the scratched pattern marks are too shallow and belong to an incorrect pattern.
5 Conclusion
On the surface of the finished workpiece after shaving, or on the surface of the workpiece after finishing, finishing and grinding, the desired pattern can be scraped as needed. There are three purposes for scratching: one is to make the surface of the workpiece beautiful; the other is to form a good lubrication condition between the moving pairs; the third is to judge the degree of wear on the surface of the workpiece by the disappearance of the pattern.
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