Gun Drilling – The Ultimate Guide
Drilling allows you to create circular holes in solid materials by utilizing a rotating tool. It is one of the most common machining operations offering you a way to produce holes with defined diameters and depths. There are different approaches to drilling, and here we discuss gun drilling.
What is Gun Drilling?
With gun drilling, you can achieve precise and deep drilling operations across a host of materials. This drilling approach was initially used in making gun barrels, from whence it drew its name. Nonetheless, gun drilling as a process has evolved finding use in high precision drilling operations.
With gun drilling, you can achieve straight holes of immense depth with a length-to-diameter ratio over 300:1. Coolant is delivered through the drilling tool’s hollow allowing achievement of a smooth surface finish thought heat removal and chip evacuation.
Advantages of Gun Drilling on Lathe
Utilizing gun drilling on a lathe combines the lathe machine’s versatility and gun drilling precision. Here are some advantages in configuring your drilling equipment this way:
- The lathe allows you to align the gun drilling tool to the workpiece. This way, you achieve impressively straight and deep holes especially in workpieces that are long and slender to high accuracy.
- The tolerance levels in gun drilling are very tight. With a lathe machine, you can repeat gun drilling operations to consistent results.
- Rotation of the lathe machine promotes a steady feeding process ensuring you achieve a smooth surface finish without need post-processing.
- Implementing a lathe in your gun drilling operation offers stability to the process reducing error of misalignment and tool deflection. This way, your gun drilling operation is efficient allowing maximum achievement of length-to-diameter ratio.
- The lathe machine’s coolant supply system ensures constant delivery to the gun drilling tool allowing enhanced chip evacuation. With such, you experience reduced clogging and even tool failure when making holes over extended lengths.
- The versatility of lathe machines allows you to perform gun drilling operations on workpieces of diverse size. Workpieces of different diameters and lengths can be held in a lathes machine before drilling operation.
- The stability offered by the lathe machine ensures controlled cutting conditions, minimizing shock loads and vibrations. This helps in extending tool life ensuring you derive maximum operation efficiency.
- By combining lathe and gun drilling equipment, you reduce set up time and cost required when compared to utilizing multiple equipment. This is more efficient.
How to Choose Gun Drilling Machine
The success of your gun drilling operation will be pegged on your choice of drilling machine. Your choice is ideally influenced by several factors some of which are captured below:
· Material Type
You can gun drill various materials with differing physical and mechanical properties. While some materials like aluminum are soft others like steel are hard. Consequently, a gun drilling machine used for aluminum will not work effectively on steel.
· Hole Parameters
The key parameters influential in your selection of a gun drilling machine are the diameter and depth. A maximum and minimum value often between 1mm to 50mm is provided for the diameter. The depth is determined by the length-to-diameter ratio often reaching 300:1.
· Production Volume
You can have a manually operated or CNC gun drilling machine depending on the number of articles you intend to produce. A gun drilling machine with CNC control constitutes automatic features and systems ideal for high-volume production.
· Workpiece Size and Shape
The size of the workpiece dictates the bed length of the machine and its capacity to hold a workpiece. Where your workpiece is long, your gun drilling machine should comfortably accommodate it. Furthermore, the machine should have ideal fixtures to securely hold a workpiece of any shape.
· Machine Structure
Gun drilling is a highly precise operation that does not take well to issues like vibration and stress loads. Otherwise, it may lead to hole inefficiencies and at worst tool damage. A machine with features like guide ways and ball screws provides stability for smooth tool movement.
· Tool Compatibility
Given the varying tools required for the gun drilling operation, some machines can only support certain tooling. Other machines are highly versatile with capacity to accommodate a diverse spectrum of tooling. Unless undertaking highly specialized fun drilling operations, the latter is always ideal.
· Coolant and Chip Evacuation
Owing to the cutting depths achieved by gun drilling, it is necessary to have a system that can effectively conduct coolant. A high pressure system is preferable with a collection tray to enable recycling. This way you can effectively remove chippings and lubricate the tooling.
· Cost
The cost of acquiring a drilling machine will vary with machine’s size and level of automation which is determined by your scale of operation. For a low volume operation, it beggars no need to invest in large automated machines. Understand also operational costs are directly related to size.
Steps in Gun Drilling Process
In undertaking gun drilling, there are certain essential steps you implement to achieve the deep and precise holes. Gun drilling is a highly specialized operation that requires a sound setup and execution for quality results.
1. Setting up
First, you secure the workpiece onto the machine such that it remains unmoved during the drilling operation. You can use extra support fixtures like bushings and steady rests for long workpieces. Thereafter, you mount the gun drill onto the tool holder of the machine.
2. Alignment
A guide bushing is effective in helping you align the drill with the location you intend to create a hole. This way it keeps the gun drill on lock ensuring there is no deviation. You then center the tip of the drill to your hole location.
3. Drilling
Rotating the gun drill at high speed initiates the drilling process. A slow feed rate is ideal as you guide the drill tip as it cuts into the material. A slow feed rate ensures you do not have chip accumulation helping you achieve a smooth surface finish. It also prevents tool wear and premature damage.
4. Coolant Injection
This happens simultaneously with the drilling process. It serves multiple roles; cooling the tool owing to friction induced heat and flushing out chips. The coolant is conducted via the hollow of the gun drill to the point of action.
5. Chip Removal
Continuously removing chips during the drilling process is necessary to prevent path blockage and ensure high quality finish. You deliver the coolant under high-pressure sufficient enough to forcefully eject them from the hole cavity.
6. Hole Inspection
Inspection seeks to confirm the dimensional accuracy of the hole and quality in relation to straightness and surface finish. Upon completion of the drilling process, you retract the drill to carry out inspection. Precise tooling like laser-based gauges are essential to confirm hole specs.
Factors to Consider in Gun Drilling Process
When carrying out a gun drilling operation, you need to display careful control over multiple parameters for a successful outcome. Captured below are some of the important factors for consideration:
· Material Properties
Hardness, toughness, ductility and abrasiveness of the workpiece material impact the gun drilling process. Hard and abrasive materials require more rigid tooling, slower cutting speeds and high-pressure coolant. Ductile materials produce stringy chips, which may affect chip evacuation.
· Tool Design
Consider the tool’s cutting edge ensuring it offers balance between material removal and formation of chips. Match your gun drill to the desired hole diameter which affects feed rate, coolant flow and length-to-diameter ratio. Utilize HSS as tool material for soft materials and carbide for harder materials.
· Hole Specifications
The primary parameter to consider when gun drilling is the length-to-diameter ratios. While you can achieve upwards of a 300:1, you need to have proper tooling to maintain accuracy and address chip evacuation. Consider using guide bushings at the beginning to prevent deflection.
· Feed Rate and Cutting Speed
When gun drilling, it is advisable to use low feed rates for enhanced precision and reducing tool wear. Having a high cutting speed helps produce a smooth cut. Nonetheless, you need to balance your feed rate and cutting speed depending on the workpiece material.
· Coolant System
Use high-pressure coolant systems especially for deep holes to prevent chip blockages, overheating, poor surface finish and tool wear. There are different coolant types you can select from synthetic fluid to water-soluble oils depending on the cutting conditions and material.
· Chip Control
If left unmanaged chips generated during gun drilling can cause blockages, tool damage, surface defects and/or hole deviation. Using a gun drill with spiral groove helps evacuate the chips. You can also consider incorporating chip breakers simplify the evacuation process.
· Workpiece Support
Preventing movement during gun drilling is essential and clamping the workpiece can be useful to this regard. When working on long workpieces, utilize bushings and steady rests or bushings for additional support preventing deflection.
· Tool Wear
After extended use, you are bound to experience tool wear. Monitor wear rate through regular inspection and consider interventions like replacement. Additionally, you can apply wear-resistant coatings like titanium nitride, to extend tool life by reducing friction, and thus improving performance.
Key Applications
There are several applications in which there’s need for straight, deep, smooth and precise holes of high accuracy. As a result, you find use of gun drilling as a fabrication technique across the following industries:
· Aerospace Industry
The precise, small-diameter holes in fuel injector nozzles used in controlling fuel flow in aircraft engines are gun drilled. Parts of the landing gear are made with hollow channels for structural aptitude. Additionally, hydraulic systems used to transmit high-pressure fluids are bored via gun drilling.
· Automotive Industry
High-precision fuel injectors utilize gun drilling in achieving their effective design used to support combustion. Engine components such as transmission and crank shafts are fabricated via this technique to provide structural integrity and lubrication channels.
· Weapons Manufacture
As noted prior, gun drilling was used in making gun barrels from where it derived its name. To this day, gun drilling is the technique used to make barrels for handguns like rifles and shotguns. It also finds use fabricating artillery shells and munitions as well as rocket components.
· Medical Devices
Surgical instruments like biopsy needles and endoscopic tools utilize gun drilling to fashion precise straight, deep holes. You also utilize this method in fabricatingorthopedic implants requiring hollow channels for placement in the body.
· Energy Sector
Gun drilling creates deep holes for tool balance and weight distribution in drill collars used in oil exploration. Hydraulic systems like manifolds and valves are fabricated by using gun drilling equipment. Turbine blades powered by steam or gas use gun drilling to implement passages for heat dissipation.
· Mold and Die Making
Gun drilling is useful in creating highly accurate cooling channels within molds for uniform cooling and thus reduced cycle times. When used in precision die making, gun drilling helps in the designing of stamping dies and other forging processes.
· Heavy Equipment and Machinery
Fluid channels in hydraulic cylinders used in heavy machinery are fabricated this way achieving high accuracy. Additionally, spindles in machine tools utilize cylindrical paths for cooling and lubrication made by gun drilling.
FAQs
1. What is the difference between gun drilling and BTA drilling?
Gun drilling and BTA (Boring and Trepanning Association) drilling are both deep hole drilling techniques. Nonetheless, gun drilling finds typical use in creating holes with smaller depths and diameters usually between 1-50 mm. BTA drilling can achieve holes with large-diameters typically over 50 mm.
2. How deep can a Gun Drill go?
Different factors affect the maximum depth achievable with a gun drill such as hole diameter and material type. However, a gun drill can typically achieve a length-to-diameter ratio in excess of 300:1. However, the higher the diameter the lower thelength-to-diameter ratio.
3. What is the Limitation of Gun Drilling?
We have mentioned the primary advantages of utilizing gun drilling for your project. However, it is not short of limitations as follows:
- Compared to other drilling approaches, gun drilling is comparatively slower especially for larger holes resulting in longer cycle times.
- Gun drilling is only viable with small-diameter holes (between 1-50mm), and not well-suited for drilling holes with very large diameters.
- Chip evacuation is challenging particularly at greater depths resulting in the observation of increased tool wear and poor surface finish.
- The slender design of gun drills coupled with a single cutting edge, makes them prone to increased wear and potential breakage. This is especially true at high depths and when use on harder materials.
- Drilling efficiency when used on harder or tougher materials like hardened steels and super alloys is greatly reduced.
- While capable of achieving achieve extreme depth-to-diameter ratios, attaining straightness, accuracy and chip removal becomes increasingly difficult beyond 300:1.
4. What is the Tolerance of Gun Drilling?
High precision is one of the primary advantages of gun drilling ideal where tight tolerances and accurate hole positioning are critical. While the workpiece material and machine setup can affect tolerance, gun drilling can achieve dimensional tolerances of ±0.0008″ to ±0.002″.
Conclusion
The gun drilling process is a highly effective technique when furnishing small diameter holes and channels to high accuracy and consistency. Its versatility allows you to implement it in your workshop for small projects and in large production floors to tight tolerances.
Related Resources:
Drilling Machines – Source: TSINFA
Radial Drilling Machine Parts – Source: TSINFA
Drilling and Milling Machines – Source: TSINFA
Drilling Process – Source: WIKIPEDIA
Drilling Machine Manufacturers – Source: TSINFA
