Disadvantages of twist drill
Although the geometric shape of twist drill is more reasonable than that of flat drill, it still has the following disadvantages:
(1) The internal and external difference of the rake angle of each point on the main cutting edge of the standard twist drill is too large. The rake angle of the main cutting edge of the outer edge of the drill bit is about+30; However, the rake angle near the drill center is about-30, and the rake angle near the drill center is too small, which leads to large chip deformation and large cutting resistance. However, the rake angle near the outer edge is too large, and the strength of the cutting edge is often insufficient when machining hard materials.
(2) The cross blade is too long, and the front angle of the cross blade is very negative, reaching -54 ~-60, which will produce a great axial force.
(3) Compared with other types of tools, the main cutting edge of standard twist drill is very long, which is not conducive to chip separation and chip breaking.
(4) The secondary rake angle of the secondary cutting edge at the edge zone is zero, which leads to the increase of friction between the secondary rake face and the hole wall, the increase of cutting temperature, the greater wear of the outer edge angle of the drill bit and the worse surface roughness.
Technical requirements for twist drill bits
Twist drill is the most widely used drill bit in industrial manufacturing, and we generally use twist drill. Length-diameter ratio of drill bit When technicians choose the most suitable drill bit type for a specific hole processing task, they need to calculate the length-diameter ratio of the drill bit. The aspect ratio is the ratio of the depth of the hole to be machined to the diameter of the drill bit. For example, if the diameter of the drill is 12.7mm and the depth of the hole to be machined is 38. 1mm, the aspect ratio is 3: 1. When the aspect ratio is about 4: 1 or less, the chips cut by the cutting edge of most standard twist drills can be discharged smoothly. When the aspect ratio exceeds the above range, a specially designed deep hole drill is needed to realize effective machining. The standard product of twist drill adopts national standards, which is equivalent to adopting international standards. Once the length-diameter ratio of the hole to be machined is greater than 4: 1, it is difficult for the standard twist drill to push the chips away from the cutting area and out of the hole, and the chips will soon block the chip discharge groove of the drill. At this time, it is necessary to stop drilling, pull the drill bit out of the hole, remove the chips in the chip removal groove, and then drill in to continue cutting. The above operations need to be repeated many times before the required hole depth can be machined. This drilling method is usually called "pecking" method. Machining deep holes by "pecking" method will shorten tool life, reduce machining efficiency and affect the quality of machining holes. Every time the drill bit is pulled out of the hole and re-inserted into the hole after chip removal, it may deviate from the center line of the hole, thus making the aperture larger and beyond the specified dimensional tolerance range. In order to solve the problem of deep hole machining, in recent years, bit manufacturers have developed two new types of deep hole machining bits: ordinary parabolic bits and wide-edged parabolic bits.
What brand of twist drill is good?
1. Far East TDC, an overseas acquired hardware enterprise, a large twist drill manufacturer and industry leader, Dalian Far East Tool Co., Ltd.
2. Tiangong TG high-tech enterprise, one of the leading production bases of high-speed steel/cutting tools, a large twist drill manufacturer, Jiangsu Tiangong Tool Co., Ltd..
3. Feida is one of the largest producers of high-speed tool steel in the world, a high-tech enterprise, an international enterprise group, and Jiangsu Feida Bit Co., Ltd..
4. Shanggong, founded in 1949, is one of the most influential brands in the domestic tool industry, a famous brand product in Shanghai, Shanghai Tool Factory Co., Ltd.
5. Bosch electric tools started in Germany 1886. It is a world brand, a leading manufacturer of electric tools in the world and an influential brand in the industry. Bosch Electric Tool (China) Co., Ltd.
6. Link Link Harbin Measuring Tool Group Co., Ltd., one of the larger precision measuring tool manufacturers in China, and the leader in China tool industry.
7. Fangda Wang Quanguo Drill (Construction) Industrial Base is a well-known enterprise, one of the top ten twist drill brands, a well-known brand in the domestic hardware tool industry, and China Fangda Holdings Co., Ltd.
8. Chuanpai was founded in 1956. It is a key manufacturer of measuring tools, a high-tech enterprise and Chengdu Liangcheng Tool Group Co., Ltd.
9. Black & Dacker Black & Decker1910 originated in the United States. Decker Black & Decker in Dacker is the world's most famous manufacturer of electric tools/household appliances, and the world's first portable electric drill with a gun handle. The company is Stanley Black & Dacker.
10. Harbin No.1 Tool Manufacturing Co., Ltd., one of the largest production bases of precision tools/numerical control tools in China, is a large-scale backbone enterprise of key equipment industry in China.
The top ten brands of twist drills are well-known brands in the market. Although the price may be higher, the service life is longer and the material is better. You can choose from them. If your economic situation is relatively average, you can also consider choosing well-known twist drill brands in the market: Heyigong, DLTC, Bailey Kugel, Zhengbang, Guling Cobalt Collar and Dangong. Although it is not as well-known as the top ten brands of twist drills, it is also safe and reliable.
Grinding method of twist drill bit
"1." The cutting edge is flat against the grinding wheel surface. "
This is the first step in the relative position between the drill bit and the grinding wheel. Students often lean on the grinding wheel and start sharpening before the cutting edge is leveled. This is definitely not going to wear well. The "cutting edge" here is the main cutting edge, and "leveling" means that the main cutting edge of the grinding part is in a horizontal position. "Grinding wheel surface" refers to the surface of grinding wheel. "Shit" means approaching slowly. At this time, the drill bit will not touch the grinding wheel.
"The drill shaft is inclined to release the rake angle."
This refers to the positional relationship between the bit axis and the grinding wheel surface. The rake angle is half of the vertex angle 1 18 2O, which is about 60. This position is very important, which directly affects the size of the top angle of the drill bit, the shape of the main cutting edge and the oblique angle of the cross edge. Students should be reminded to remember the 60 angles in the commonly used triangles of 30, 60 and 90, so that students can master them easily. Formula 1 and formula 2 both refer to the relative position of the drill bit before sharpening, which should be considered as a whole. Don't neglect to set an oblique angle or an oblique axis to balance the cutting edge. These mistakes are often made in actual operation. At this point, the drill bit is ready to contact the grinding wheel at the correct position.
"3." Grind the back from the edge to the back. "
This refers to grinding slowly along the whole side from the cutting edge of the drill bit. This facilitates heat dissipation and sharpening. On the basis of stabilizing Formula 1 and Formula 2, at this time, the drill bit can lightly touch the grinding wheel for a small amount of sharpening. When sharpening a knife, observe the uniformity of sparks, adjust the pressure in time, and pay attention to the cooling of the drill bit. When grinding is resumed after cooling, it is often difficult to grasp the position of the first type and the second type, and the correctness of their positions is often changed involuntarily.
4. Swing your tail up and down.
This action is also very important in the grinding process of the drill bit. Some students often change "swinging up and down" to "rotating up and down" when grinding, so that the other main edge of the drill bit is destroyed. At the same time, the tail of the drill bit cannot be tilted above the horizontal center line of the grinding wheel, otherwise the cutting edge will be dull and unable to cut.
Use and maintenance of twist drill
1. When using a twist drill, first insert the bolt joint of the horizontal handle part into the directional groove of the movable connecting nut of the drill rod, tighten the connecting nut counterclockwise, then insert it into the pre-planned drilling area, press it by hand and screw it into the soil clockwise. When it rotates about 200~250 mm, the borehole will be pulled up (it will be laborious and inconvenient to pull it too deep), and the soil in the drill rod will be removed, that is, the soil sample at a distance from this.
2. If it is necessary to drill deeper after reciprocating to 1m, loosen the connecting nut of the drill bit clockwise, remove the horizontal handle, connect the bolt head part of the second drill rod part and insert it into the movable connecting screw of the drill bit part, tighten the connecting nut clockwise, then connect the horizontal handle part and the drill rod as above (1) and continue to work, and the third, fourth and fifth paragraphs are the same as above until the work is completed.
3. Twist drill pipe is made of seamless steel pipe with pu wall, which is not suitable for use in hard soil area.
4. After each use, it should be cleaned, dried and coated with antirust grease to prevent rust.