Commonly Used Deep-Hole Processing Machine Tools
Deep-hole processing machine tools are a general term for specialized machines that rely on specific machining techniques to produce deep holes with aspect ratios greater than 10. These specific machining techniques include deep-hole drilling, deep-hole rolling, and deep-hole honing. Deep-hole machines represent advanced and efficient deep-hole machining technologies. This chapter primarily introduces the structures and principles of gun drills, deep-hole boring and drilling machines with internal chip removal, deep-hole honing machines, and dual-processing system three-axis deep-hole boring and drilling machines.

4.1 Gun Drills
4.1.1 Working Principle of Gun Drills
Gun drills are typical deep-hole drilling machines with external chip removal. Gun drills are primarily used for drilling small-diameter deep holes. They require high cutting fluid pressure and are one of the most common deep-hole drilling machines. The drilling system of a gun drill utilizes external chip removal. Cutting fluid flows through the interior of the hollow drill rod to the drill head for cooling and lubrication, and chips are then discharged through V-grooves on the drill bit and the drill rod's exterior. The following diagram illustrates the operating principle of a typical gun drill.

A gun drill consists of a bed, spindle box, chip collector, oiler, drill rod box, workpiece support, drill rod holder, feed system, high-pressure coolant system, CNC electrical system, and hydraulic system. The workpiece is held tight by the spindle box and the conical top plate of the chip collector. The drill bit is driven by the drill rod box to rotate at high speed, achieving cutting motion. A servo motor drives a ball screw to push the drill rod box, achieving feed motion. The oiler injects high-pressure cooling oil from the rear end of the drill bit, passing through the drill's inner bore directly into the workpiece's cutting area. Drill chips are flushed by the coolant along the drill's chip guide grooves into the chip collector, where they enter the chip hopper. The coolant then passes through filter paper and magnetic filtration before returning to the oil tank for further use.
4.1.2 Main Parameters of Gun Drill Machines
Gun drill machines can drill holes with diameters ranging from 3 to 40 mm, with a maximum drilling depth of 2500 mm. Generally, the cutting speed v = 1.1-1.65 m/s, the feed rate f = 0.015-0.03 mm/r, the cutting fluid pressure P = 2.5-6.0 MPa, and the cutting fluid flow rate O = 10-100 L/min. The main parameters of a typical deep-hole gun drilling machine are shown in Table 4.1.

4.1.3 Typical Gun Drilling Machines
In production, there are many types and specifications of gun drilling machines. The following are commonly used.
1. Conventional Gun Drilling Machines
Conventional gun drilling machines are the most common type of gun drilling machine, primarily used for drilling small-diameter deep holes in rotating and non-rotating parts. Based on the spindle layout, whether the drill bit rotates, the shape of the workpiece, and the number of spindles, they can be divided into single-axis horizontal gun drilling machines, single-axis vertical three-axis gun drilling machines, and multi-axis horizontal gun drilling machines, as shown in Figures 4.2-4.4.

2. Deep Hole Gun Drilling Center
Deep hole gun drilling centers are primarily used for drilling small-diameter deep holes with complex spatial angles on complex housing and frame parts, as shown in Figure 4.5.

4.2 Deep Hole Internal Chip Removal Drilling and Boring Machine
4.2.1 Operating Principle of Deep Hole Internal Chip Removal Drilling and Boring Machine
A deep hole internal chip removal drilling and boring machine is a typical deep hole internal chip removal system machine tool capable of deep hole drilling and deep hole boring operations, primarily used for drilling and boring large-diameter deep holes. Drilling typically uses the BTA drilling method, but with the addition of certain accessories, it can also utilize the ejector and DF drilling methods. Its structure and operating principle are shown in Figures 4.6 and 4.7. The machine tool spindle drives the workpiece, while the tool performs linear feed motion. High-pressure coolant is supplied through the oiler to the gap between the outer surface of the tool bar and the hole wall, and then reaches the drill bit through the annular gap between the outer surface of the tool bar and the hole wall, cooling the drill bit and discharging the chips through the inside of the drill bar to the chip removal bucket at the back of the bed. The main component of the deep hole chip removal drilling and boring machine is the oiler, and the structure of the oiler is shown in Figure 4.8. The right end of the oiler is sealed by the drill bar seal. When the coolant enters, the high-pressure coolant can only rush to the left through the guide sleeve to the drill bit, cooling and lubricating the drilling area. The oiler has three main functions: (1) Centering the workpiece and axially tightening it. (2) Guiding the drill bit at the beginning of the drilling process. (3) Supplying coolant to the cutting area. 4.2.2 Main Parameters of Deep-Hole Boring and Drilling Machines with Internal Chip Removal
The drilling diameter range of deep-hole boring and drilling machines with internal chip removal is 40–500 mm, and the maximum drilling depth can reach 20,000 mm. The cutting fluid pressure P = 0.5–2.0 MPa, and the cutting fluid flow rate O-40–200 L/min. The main parameters of a typical deep-hole boring and drilling machine are shown in Table 4.2.

4.2.3 Typical Deep-Hole Boring and Drilling Machines with Internal Chip Removal
Common deep-hole boring and drilling machines include the following.
1. Horizontal Workpiece Rotary Deep-Hole Boring and Drilling Machines
Horizontal workpiece rotary deep-hole boring and drilling machines are the most commonly used deep-hole boring and drilling machines, primarily used to process rotating parts. They are categorized by workpiece size and weight into small, medium, and heavy-duty deep-hole boring and drilling machines, as shown in Figures 4.9–4.11.

2. Coordinate Deep Hole Boring and Drilling Machines
Coordinate deep hole boring and drilling machines are equipped with precision coordinate positioning devices and are primarily used for machining non-rotating parts. Coordinate deep hole boring and drilling machines can be divided into horizontal and column types, as shown in Figures 4.12 and 4.13.