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| TAPPING BERYLLIUM COPPER |
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Tapping is one of the most difficult metal removal tasks regardless of the work piece material. Aluminum is the easiest to tap, and the wry high strength steels are the most difficult. Beryllium copper is tapped successfully if care is taken in the selection of the tapping machine, cutting fluid, tap configuration, speeds and feeds. Since beryllium copper is much higher strength than other copper alloys, it should be classed with the tough, hard alloys rather than with softer brasses and bronzes. A machine of sufficient power should be used. The rigidity of the spindle and fixtures must ensure that the part and tap stay in alignment. Floating and torque sensitive tap holders can be used if alignment and/or tap breakage is encountered. |
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TAP
CONFIGURATION - FIGURE 4 |
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The ease with which beryllium copper alloys are tapped depends on the hardness of the material. Beryllium copper parts are usually tapped after heat treatment. However, the stress of tapping a small diameter hole may necessitate tapping the material before heat treating. The
softer the beryllium copper, the easier it is tapped. Standard ground taps can be used for most tapping operations. Forming taps have been used for tapping annealed material where good thread finish is required. If forming taps are used, the tap manufacturer’s recommended drill size should be used for the tap drill hole. This will vary considerably from the tap drill size required for cutting type taps.
Spiral pointed or chip driver taps are recommended if the tap hole is through the part or if sufficient clearance is provided for chips. Tap manufacturers have developed special grinds and flute configurations to simplify tapping tough materials.
Drastic changes in cutting speed, to improve tap performance, should be undertaken with caution. Tap life is sensitive to changes in cutting speed and the proper cutting speed must be used if maximum tool life is to be maintained.
The hook or rake angle ground on taps is standard for the various size taps, and varies little from one tap manufacturer to another. The cutting surface of a tap is along the length of the chamfer, in the case of the straight pointed tap, and along the angle of the spiral point (14°) and chamfer, in the case of the spiral pointed tap. The hook or radial rake angle will vary along the length of the cutting edge, from the end of the tap to the first full thread after the chamfer. Tap manufacturers have standardized tap geometry and no advantage is gained by altering these tried configurations. It is recommended that standard taps be used to tap beryllium copper alloys. It is important to note that coated taps will provide extended life.
The use of a cutting fluid is recommended when tapping all beryllium copper alloys. An active cutting oil, such as Cindol 3401 or equivalent, is suggested.
Recommended tapping speeds and tap configuration are shown in Table 3 and Figure. 4 |
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| Recommended tapping parameters and tool configurations - Table 3 | |||||
| ALLOY | TEMPER | CUTTING SPEED (ft./min.)* | HOOK OR RAKE ANGLE** | POINT CONFIGURATION** | NUMBER OF FLUTES |
| 25, M25M 165 | A | 50-100 | 7° | Spiral | 2-3-4 |
| H | 30-60 | 7° | Spiral | 2-3-4 | |
| AT, HT | 15-25 | 7° | Spiral | 2-3-4 | |
| 3, 10 | A | 20-150 | 7° | Spiral | 2-3-4 |
| H | 10-60 | 7° | Spiral | 2-3-4 | |
| AT, HT | 10-100 | 7° | Spiral | 2-3-4 | |
| 275C, 245C, 20C, 21C, 165C | C, A | 20-50 | 7° | Spiral | 2-3-4 |
| CT, AT | 5-10 | 7° | Skew-Shear | - | |
| 3C, 10C | C, A | 10-75 | 7° | Spiral | 2-3-4 |
| CT, AT | 10-50 | 7° | Spiral | 2-3-4 | |
| *Cutting speed is dependant
largely on the rigidity of the tool; when tapping holes smaller than about
1/8" diameter the low end of the cutting speed range should be used. **Manufacturers Standard. |
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