English 
Russian 
Hindi 
Persian 
Thai 
Malay 
Vietnamese 
Indonesian 
Myanmar 
German 
French 
Spanish 
Portuguese 
Czech 1. Cutting Parameter Selection
The selection of cutting parameters is related to the cutting process and chip formation, as well as the material of the workpiece, precision requirements, and machine tool characteristics.
1) Cutting Speed
The cutting speed is primarily determined by the tool material and is limited by the drill bit’s durability and the machine’s rpm. High-speed steel gun drills generally use a cutting speed of v = 35-70 m/min. For carbide gun drills, the cutting speed can be selected based on Table 2.1.
To achieve satisfactory results when drilling deep holes with a gun drill, it is essential to rationally select cutting parameters, tool geometry, gun drill operating parameters, tool material, and coolant. This ensures excellent machining performance and satisfactory machining quality.
1. Cutting Parameter Selection
The selection of cutting parameters is related to the cutting process and chip formation, as well as the material of the workpiece, precision requirements, and machine tool characteristics.
1) Cutting Speed
The cutting speed is primarily determined by the tool material and is limited by the drill bit’s durability and the machine’s rpm. High-speed steel gun drills generally use a cutting speed of v = 35-70 m/min. For carbide gun drills, the cutting speed can be selected based on Table 2.1.
(4) Precise guide sleeve device. The guide sleeve device completes the accurate cutting guide of the gun drill, collects and drains the chips and cutting fluid, and seals and controls the cutting fluid in the cutting area.
3. Selection of cutting fluid
The cutting fluid used in gun drills has high requirements because it directly affects the accuracy of the processed hole. It is necessary to select a special gun drill oil. Gun drill oil has the function of ensuring the formation of an oil film under high pressure to prevent dry grinding. The viscosity of gun drill oil is related to the diameter of the drill hole. The smaller the diameter, the lower the viscosity.
4. Guide hole and drill sleeve
When the gun drill starts drilling, a guide drill sleeve or guide hole must be used. The inner diameter of the drill sleeve matches the diameter of the drill bit. The inner diameter of the drill sleeve should be ground to IT6 grade. Since it is a consumable part, the drill sleeve should be replaced when the inner diameter wear of the drill sleeve exceeds 0.02mm. It is generally recommended to use a carbide drill sleeve. When the workpiece is short or the hole straightness requirement is not high, it can also be used to guide by drilling a guide hole on the workpiece. The size requirements of the guide hole can be referred to Table 2.2.
5. Failure of Gun Drills
The failure of gun drills is mainly manifested in the following aspects:
(1) When the coaxiality between the rotation axis of the drill sleeve and the drill bit is too large, the gun drill will usually fail, such as the impact of the drill tip. This impact will cause the fragile carbide tip to be unable to withstand the bending stress caused by the misalignment between the drill sleeve and the drill bit, resulting in blade breakage.
(2) If the drill bit rotates and the workpiece is fixed, the cutting force will act on different parts of the tip. When the cutting force acts on the weakest part (i.e., the tip corner), the tip will break.
(3) When the gun drill length increases, the rigidity of the tool decreases, causing the tool bar to vibrate and lead to fatigue failure.
(4) Excessive gap between the drill sleeve and the drill bit will cause tool failure. At this time, the side edge of the gun drill cuts off a large amount of workpiece material, and excessive cutting force will cause the side edge to break.
(5) Insufficient coolant supply is also a cause of tool failure. It will cause chips to accumulate in the chip groove. These squeezed chips will form a blockage, causing excessive torque to act on the gun drill. When the V-groove of the gun drill is blocked, the cutter head will separate from the tool shank.
2.1.4 Gun drill sharpening
1. Gun drill blunting standard
Generally, the blunting standard of carbide gun drills is measured by the VB value of the back wear of the gun drill.
(1) For gun drills with do<15mm, VB=0.2~0.4mm;
(2) For gun drills with do>15mm, VB=0.4~0.6mm.
When the width of the back cutting edge of the gun drill outer edge exceeds the blunting standard, the gun drill must be sharpened to prevent the cutting force from increasing and causing the cutter head to break.
2. Issues to note when sharpening carbide gun drills
(1) The grinding of the gun drill should be timed forced grinding. That is, when the back cutting edge wear of the tool reaches the blunting standard, it should be re-sharpened. (2) When grinding, a sharpening fixture and a dedicated sharpener must be used. Do not sharpen the drill bit by hand.
(3) When grinding, the force applied to the drill bit should be directed toward the cutter pad to prevent the drill rod from shaking and causing damage to the tool. The amount of feed should not be too large each time to prevent the carbide drill bit from cracking or breaking, causing personal injury.
(4) After the five blade surfaces of the drill bit are ground, the edges between the drill bit back surface and the drill bit guide part should be manually rounded on the grinding wheel.
(5) Gun drills need to be re-sharpened on a dedicated diamond grinding wheel.
(6) The dust generated by sharpening the carbide part of the gun drill is harmful to the body, so protective glasses and a mask must be worn.
3. Standard sharpening angle of gun drills
The standard sharpening angle of gun drills is shown in Figure 2.14.
4. Gun Drill Regrinding
A gun drill can be regrinded after becoming blunt to ensure proper function. The number of times a gun drill can be regrinded depends on the hole diameter tolerance and the workpiece material. Typically, the number of regrindings is 15-20, with a total drilling depth of 10-20 mm after each regrinding. Regrinding is typically performed on a tool grinder or gun drill sharpening machine using a dedicated fixture. Sharpening parameters are determined based on production conditions and the material being processed, referring to standard gun drills.
(4) Precise guide sleeve device. The guide sleeve device completes the accurate cutting guide of the gun drill, collects and drains the chips and cutting fluid, and seals and controls the cutting fluid in the cutting area.
3. Selection of cutting fluid
The cutting fluid used in gun drills has high requirements because it directly affects the accuracy of the processed hole. It is necessary to select a special gun drill oil. Gun drill oil has the function of ensuring the formation of an oil film under high pressure to prevent dry grinding. The viscosity of gun drill oil is related to the diameter of the drill hole. The smaller the diameter, the lower the viscosity.
4. Guide hole and drill sleeve
When the gun drill starts drilling, a guide drill sleeve or guide hole must be used. The inner diameter of the drill sleeve matches the diameter of the drill bit. The inner diameter of the drill sleeve should be ground to IT6 grade. Since it is a consumable part, the drill sleeve should be replaced when the inner diameter wear of the drill sleeve exceeds 0.02mm. It is generally recommended to use a carbide drill sleeve. When the workpiece is short or the hole straightness requirement is not high, it can also be used to guide by drilling a guide hole on the workpiece. The size requirements of the guide hole can be referred to Table 2.2.
5. Failure of Gun Drills
The failure of gun drills is mainly manifested in the following aspects:
(1) When the coaxiality between the rotation axis of the drill sleeve and the drill bit is too large, the gun drill will usually fail, such as the impact of the drill tip. This impact will cause the fragile carbide tip to be unable to withstand the bending stress caused by the misalignment between the drill sleeve and the drill bit, resulting in blade breakage.
(2) If the drill bit rotates and the workpiece is fixed, the cutting force will act on different parts of the tip. When the cutting force acts on the weakest part (i.e., the tip corner), the tip will break.
(3) When the gun drill length increases, the rigidity of the tool decreases, causing the tool bar to vibrate and lead to fatigue failure.
(4) Excessive gap between the drill sleeve and the drill bit will cause tool failure. At this time, the side edge of the gun drill cuts off a large amount of workpiece material, and excessive cutting force will cause the side edge to break.
(5) Insufficient coolant supply is also a cause of tool failure. It will cause chips to accumulate in the chip groove. These squeezed chips will form a blockage, causing excessive torque to act on the gun drill. When the V-groove of the gun drill is blocked, the cutter head will separate from the tool shank.
2.1.4 Gun drill sharpening
1. Gun drill blunting standard
Generally, the blunting standard of carbide gun drills is measured by the VB value of the back wear of the gun drill.
(1) For gun drills with do<15mm, VB=0.2~0.4mm;
(2) For gun drills with do>15mm, VB=0.4~0.6mm.
When the width of the back cutting edge of the gun drill outer edge exceeds the blunting standard, the gun drill must be sharpened to prevent the cutting force from increasing and causing the cutter head to break.
2. Issues to note when sharpening carbide gun drills
(1) The grinding of the gun drill should be timed forced grinding. That is, when the back cutting edge wear of the tool reaches the blunting standard, it should be re-sharpened. (2) When grinding, a sharpening fixture and a dedicated sharpener must be used. Do not sharpen the drill bit by hand.
(3) When grinding, the force applied to the drill bit should be directed toward the cutter pad to prevent the drill rod from shaking and causing damage to the tool. The amount of feed should not be too large each time to prevent the carbide drill bit from cracking or breaking, causing personal injury.
(4) After the five blade surfaces of the drill bit are ground, the edges between the drill bit back surface and the drill bit guide part should be manually rounded on the grinding wheel.
(5) Gun drills need to be re-sharpened on a dedicated diamond grinding wheel.
(6) The dust generated by sharpening the carbide part of the gun drill is harmful to the body, so protective glasses and a mask must be worn.
3. Standard sharpening angle of gun drills
The standard sharpening angle of gun drills is shown in Figure 2.14.
4. Gun Drill Regrinding
A gun drill can be regrinded after becoming blunt to ensure proper function. The number of times a gun drill can be regrinded depends on the hole diameter tolerance and the workpiece material. Typically, the number of regrindings is 15-20, with a total drilling depth of 10-20 mm after each regrinding. Regrinding is typically performed on a tool grinder or gun drill sharpening machine using a dedicated fixture. Sharpening parameters are determined based on production conditions and the material being processed, referring to standard gun drills.
