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Drilling a hole

Drilling a hole
 

​Drilling is often carried out late in the manufacturing process, after previous operations have already enhanced the initial component’s value. The drilling application, although seemingly simple, is a complex operation that can have significant consequences if the tool malfunctions or is run beyond its capacity.

 

Initial considerations for drilling a hole

1. The hole

​The three most basic considerations for drilling a hole are:

  • Hole diameter
  • Hole depth
  • Hole quality

​Hole type and required precision affect tool choice. Drilling can be affected by irregular or angled entry/exit surfaces and by cross holes.

Hole types

Through
Blind
Chamfer
Step
 
Entry
Exit
Cross
 
  1. Holes with clearance for bolts
  2. Holes with a screw thread
  3. Countersunk holes
  4. Holes that have a good fit
  5. Holes for tubes (heat exchangers)
  6. Holes that form channels
  7. Holes to remove weight for balancing
  8. Deep/coolant hole

2. The component

​After the required hole has been analyzed, take a look at the workpiece material, component shape and quantity.

Workpiece material

  • Does the material have good chip-breaking qualities? Long or short chipping material?
  • Machinability?
  • Material hardness?
  • Alloy elements?

Component shape

  • Is the component rotation symmetric around the hole, i.e. can the hole be machined with a non-rotating drill?
  • Is the component stable, or are there thin sections that can cause vibration?
  • Can the component be fixed in place? What stability problems need to be considered?
  • Is a tool extension needed? Do long tool overhangs need to be used?

Quantity

​The batch size affects which drill to use.

  • Large batch size – use optimized or custom drills
  • Small batch size – use drills optimized for versatility

3. The machine​

​It is important to know how to perform a secure and productive drilling operation in the machine. The machine influences the choice of:

  • Type of operation
  • Which type of tool holders and/or collets to use

​Always consider the following:

  • Machine stability, in general and especially the spindle
  • Is the spindle speed (rpm) enough for small diameters?
  • Coolant supply. Is the coolant volume sufficient for large-diameter drills?
  • Is coolant pressure sufficient for small-diameter drills?
  • Clamping of the workpiece. Is it sufficiently stable?
  • Horizontal or vertical spindle? A horizontal spindle enables better chip evacuation
  • Power and torque. Is the power sufficient for large diameters? If not, can a trepanning drill be used, or can helical interpolation with a milling tool be used instead?
  • Is there limited space in the tool magazine? If so, a step and chamfer drill can be a suitable solution

Tool holding

​Productivity is not only influenced by grade and geometry, but also by tool holding and the ability to clamp securely and precisely. Always use the shortest possible drill and overhang.

​Consider a modular tooling system designed for all metal-cutting operations, including all hole-making methods. With such a system, the same cutting tools and adapters can be used in different applications and machines. This makes it possible to standardize, using one tooling system for the entire machine shop.

​Tool run-out

​Minimum tool run-out is essential for successful hole drilling. The run-out should not exceed 20 microns. Alignment must be parallel for:

  • Close hole tolerance and straightness
  • Good surface finish
  • Long and consistent tool life
 

Choice of method

Counter bore – strategies

One tool solution
  • Step drilling / counter bore
  • Drill type 4/5
 
Advantages
+ Customized tools
+ Fastest method
 
Disadvantages
- Less flexible
Two-tool solution
 
Advantages
+ Standard tools
+ Relatively flexible
 
Disadvantages
- Two tools
- Requires two tool positions
- Longer cycle time
 

Step and chamfer – one-drill strategy

Drill type 1
Standard
 
Drill type 2
2-diameter drill (pilot + body diameter)
With pilot and chamfer. Non-body diameter cutting
 
Drill type 4
2-diameter drill (pilot + body diameter)
With pilot, chamfer and body diameter cutting
 
Drill type 5
3-diameter drill (pilot + step + body diameter)
With pilot, step and chamfer. Non-body diameter cutting
 
Drill type 6
3-diameter drill (pilot + body diameter)
With pilot, step and chamfer and body diameter cutting
 
 

Drilling operations

Drilling operations

​Achieving the required hole quality at the lowest cost per drilled hole depends on making the right tool choice. These different types of holes require different tool considerations:

  • Small to medium diameter holes
  • Large diameter holes
  • Deep holes
  • Micro holes
 

Drilling small to medium diameter holes

​When drilling small to medium holes, there are three different drilling solutions to choose from: solid carbide drills, exchangeable-tip drills and indexable insert drills. Hole tolerance, length and diameter are three important parameters to consider when selecting drill type. Each solution has its advantages in different applications.

 

Drilling large holes

​There are three options for drilling large holes with limited machine power:

  • Use a trepanning tool
  • Enlarge the hole with a boring tool
  • Use helical interpolation with milling tools

​​Stability of both the component and machine is important when drilling large holes. Machine power and torque can also be limiting factors. From a productivity point of view, drilling tools are a superior choice – 5 times faster than milling a hole using helical interpolation. A trepanning tool can, however, only be used in through-hole applications. Milling cutters have the lowest power and torque requirements by far.

 

Drilling deep holes

Pilot hole drilling

​​Pilot drills are designed to work with drills for deep holes, to give maximum accuracy in drill location and minimum hole run-out.

Speeds and feeds

​​The speeds and feeds recommended for use with the drills for deep holes have been calculated to give good tool life combined with maximum productivity. The speeds and feeds given provide a good starting point; each application may require adjustments to speeds and feeds to achieve optimum results.

 

Drilling micro holes

Speeds and feeds

​​The speeds and feeds recommended for use with micro drills have been calculated to give good tool life combined with maximum productivity. The speeds and feeds given provide a good starting point; each application may require adjustments to speeds and feeds to achieve optimum results.

Coolant

​​Coolant pressure is a key factor in micro drilling. Inadequate coolant pressure or volume can lead to premature tool failure. We strongly recommend use of high coolant pressures. The typical pressure recommended is between 40–70 bar.

 

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