The three most basic parameters for the hole are:
- Hole diameter
- Hole depth
- Hole quality
The hole type and the required precision affect tool choice. Drilling can be affected by irregular or angled entry/exit surfaces and by cross holes.
- Holes with clearance for bolts
- Holes with a screw thread
- Countersunk holes
- Holes that have a good fit
- Holes for tubes (heat exchangers)
- Holes that form channels
- Holes to remove weight for balancing
- Deep/coolant hole
When the hole is analyzed, have a look at the workpiece material, component shape and quantity.
- Does the material have good chip breaking qualities? Long or short chipping material?
- Material hardness?
- Alloy elements?
- 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 vibrations?
- Can the component be fixed in place? What stability problems need to be considered?
- Is a tool extension needed to reach the surface where the hole shall be drilled? Need to use long tool overhangs?
The batch size affects which drill to use.
- Large batch size - Use optimized drill, TM/Special drill
- 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 coolant volume enough for large diameter drills?
- Is coolant pressure enough for small diameter drills?
- Clamping of the workpiece, is the stability sufficient?
- Horizontal or vertical spindle? A horizontal spindle enables better chip evacuation
- Power and torque, is the power enough for large diameters? If not, can a trepanning drill be used or can helical interpolation with a milling toll be used instead?
- Is there limited place in the tool magazine? Then a step and chamfer drill can be a suitable solution