Tips for achieving good hole quality
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Chip evacuation
Make sure chip evacuation is satisfactory. Chip jamming affects hole quality and reliability/tool life. Drill/insert geometry and cutting data are crucial.
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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 component is fixed and stable. Establish correct feed rates for irregular, angular surfaces and cross holes.
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Tool life
Check insert wear and establish pre-determined tool life program. The most effective way to supervise drilling is by using a feed force monitor.
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Maintenance
Change insert-clamping screw regularly. Clean the tip seat before changing 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)
- Aluminium 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 often are used for welded components. The lower the hardness, carbon and sulphur 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 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 grey cast iron, but they are well 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 aluminium alloy tips
Issue: Burr formation and chip evacuation can be a problem. Poor tool life can also be present 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 certain cases (depending on the substrate) not using any coating at all.
Other: Use emulsion or mist coolant at high pressure.
Drilling titanium and Heat Resistant Alloy tips
Issue: Work hardening of 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 Nickle-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 an acceptable tool life.
Recommendations: Lower cutting speed in order to reduce heat. Adjust 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) |
Tool width | D>3-6 | D>6-10 | D>10-18 | D>18-30 | D>30-50 | D>50-80 | D>80-120 | D>120-180 | D>180-250 |
IT5 | 0.005 | 0.006 | 0.008 | 0.009 | 0.011 | 0.013 | 0.015 | 0.018 | 0.020 |
IT6 | 0.008 | 0.009 | 0.011 | 0.013 | 0.016 | 0.019 | 0.022 | 0.025 | 0.029 |
IT7 | 0.012 | 0.015 | 0.018 | 0.021 | 0.025 | 0.030 | 0.035 | 0.040 | 0.046 |
IT8 | 0.018 | 0.022 | 0.027 | 0.033 | 0.039 | 0.046 | 0.054 | 0.063 | 0.072 |
IT9 | 0.030 | 0.036 | 0.043 | 0.052 | 0.062 | 0.074 | 0.087 | 0.100 | 0.115 |
IT10 | 0.048 | 0.058 | 0.070 | 0.084 | 0.100 | 0.120 | 0.140 | 0.160 | 0.185 |
IT11 | 0.075 | 0.090 | 0.110 | 0.130 | 0.160 | 0.190 | 0.220 | 0.250 | 0.290 |
IT12 | 0.120 | 0.150 | 0.180 | 0.210 | 0.250 | 0.300 | 0.350 | 0.400 | 0.460 |
IT13 | 0.180 | 0.220 | 0.270 | 0.330 | 0.390 | 0.460 | 0.540 | 0.630 | 0.720 |
Diameter range, D (inch) |
Tool width | D>0.118-0.236 | D>0.236-0.394 | D>0.394-0.709 | D>0.709-1.181 | D>1.181-1.969 | D>1.969-3.150 | D>3.150-4.724 | D>4.724-7.087 | D>7.0879.843 |
IT5 | 0.0005 | 0.0002 | 0.0003 | 0.0004 | 0.0004 | 0.0005 | 0.0006 | 0.0007 | 0.0008 |
IT6 | 0.0003 | 0.0004 | 0.0004 | 0.0005 | 0.0006 | 0.0007 | 0.0009 | 0.0010 | 0.0011 |
IT7 | 0.0005 | 0.0006 | 0.0007 | 0.0008 | 0.0010 | 0.0012 | 0.0014 | 0.0016 | 0.0018 |
IT8 | 0.0007 | 0.0009 | 0.0011 | 0.0013 | 0.0015 | 0.0018 | 0.0021 | 0.0025 | 0.0028 |
IT9 | 0.0012 | 0.0014 | 0.0017 | 0.0020 | 0.0024 | 0.0029 | 0.0034 | 0.0039 | 0.0045 |
IT10 | 0.0019 | 0.0023 | 0.0028 | 0.0033 | 0.0039 | 0.0047 | 0.0055 | 0.0063 | 0.0073 |
IT11 | 0.0030 | 0.0035 | 0.0043 | 0.0051 | 0.0063 | 0.0075 | 0.0087 | 0.0098 | 0.0114 |
IT12 | 0.0047 | 0.0059 | 0.0071 | 0.0083 | 0.0098 | 0.0118 | 0.0138 | 0.0157 | 0.0181 |
IT13 | 0.0071 | 0.0087 | 0.0106 | 0.0129 | 0.0154 | 0.0181 | 0.0213 | 0.0248 | 0.0283 |
- The lower the IT-number, the closer the tolerance
- The tolerance for one IT class increases at larger diameters
One example:
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.
Example:
Axle ø20 mm (0.787 inch) h7
Hole ø20 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:
Hole larger than axle |
| Axle larger than hole |