Tips for achieving good hole quality
Make sure chip evacuation is satisfactory. Chip jamming affects hole quality and reliability/tool life. Drill/insert geometry and cutting data are crucial.
Stability, tool set-up
Use the shortest possible drill. Use a rigid and accurate tool holder with minimum run-out. Make sure the machine spindle is in good condition and is well-aligned. Ensure that the component is fixed and stable. Establish correct feed rates for irregular, angular surfaces and cross holes.
Check insert wear and establish a predetermined tool life program. The most effective way to supervise drilling is by using a feed force monitor.
Change the insert-clamping screw regularly. Clean the tip seat before changing the insert, and make sure to use a torque wrench. Don’t exceed maximum wear before regrinding solid carbide drills.
Drilling tips and techniques for different materials
- Low-carbon steel
- Austenitic and duplex stainless steels
- CGI (Compact Graphite Iron)
- Aluminum alloys
- Titanium and Heat Resistant Alloys
- Hard steels
Drilling low-carbon steel tips
Issue: Chip formation can be a difficult issue with low-carbon steels, which are often used for welded components. The lower the hardness, carbon and sulfur content of the steel, the longer the chips are that will be produced.
Recommendations: If problems with chip formation occur, increase the speed, vc, and decrease the feed, fn (note that in normal steels, the feed should be increased).
Other: Use high-pressure and internal coolant supply.
Drilling austenitic and duplex stainless steel tips
Issue: Austenitic, duplex and super-duplex materials can cause problems with chip formation and evacuation.
Recommendations: The correct geometry is crucial, as it enables chips to form properly and aids their evacuation. In general terms, a sharp cutting edge is preferable. If problems with chip formation occur, increasing the feed, fn, will allow the chips to break more easily.
Other: Internal coolant, high pressure.
Drilling CGI (Compact Graphite Iron) tips
Issue: CGI does not normally require extra attention. It produces larger chips than gray cast iron, but they are easily broken. Cutting forces are higher, which affects tool life. Extra wear-resistant grades are necessary. Corner wear is typical as in all cast irons.
Recommendations: If problems with chip formation occur, increase the speed, vc, and decrease the feed, fn.
Other: Internal coolant.
Drilling aluminum alloy tips
Issue: Burr formation and chip evacuation can be a problem. Tool life can also be poor due to adhesion.
Recommendations: For best chip formation, use low feed and high speed.
In order to avoid poor tool life, it may be necessary to test different coatings, minimizing adhesion. These coatings could include diamond coatings or, in certain cases (depending on the substrate), no coating at all.
Other: Use emulsion or mist coolant at high pressure.
Drilling titanium and heat resistant alloy tips
Issue: Work hardening of the hole surface affects subsequent operations. Good chip evacuation can be difficult to obtain.
Recommendations: When selecting a geometry for titanium alloys, it is preferable to have a sharp cutting edge. For nickel-based alloys, having a robust geometry is crucial. If work hardening is an issue, attempt to increase feed rate.
Other: High-pressure (up to 70 bar) coolant improves performance.
Drilling hard steel tips
Issue: Obtaining acceptable tool life.
Recommendations: Lower cutting speed to reduce heat. Adjust the feed rate in order to obtain acceptable chips that can be easily evacuated.
Other: Emulsion with a high mixture.
Hole tolerance tips
The dimensions of a hole can be divided into three parameters:
- The nominal value (the theoretically exact value)
- The tolerance width (designated IT acc. to ISO)
- The position of the tolerance (designated by capital letters acc. to ISO)
Dmax minus Dmin is the tolerance width also called IT.
|Diameter range, D (mm)|
|Diameter range, D (inch)|
- The lower the IT-number, the closer the tolerance
- The tolerance for one IT class increases at larger diameters
Nominal value: 15.00 mmTolerance width: 0.07 mm (IT 10 acc. to ISO)Position: 0 to plus (H acc. to ISO)
Hole and axle tolerances
The hole tolerance is often connected to the tolerance of an axle that should fit the hole.
Axle Ø 20 mm (0.787 inch) h7Hole Ø 20 mm (0.787 inch) h7
Axle tolerance position is designated by lower-case letters that correspond to the hole tolerances. The figure below provides a complete picture:
| ||Axle larger|