Gear cutting – milling – or planing – Gear cutting – Gear tooth shape generating
Patent
1989-05-05
1990-11-20
Schmidt, Frederick R.
Gear cutting, milling, or planing
Gear cutting
Gear tooth shape generating
407 26, B23F 2116
Patent
active
049714872
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a method for cutting gears, particularly to a method for cutting an involute gear and simultaneously chamfering its addendum.
BACKGROUND ART
In conventional hob cutters for cutting involute gears having chamfered tooth profiles, the pressure angle exhibited by the rack of teeth on the hob, the "hob tooth profile," is the same as the nominal pressure angle of the gear to be formed. It is also known to reduce the pressure angle on the hob tooth profile to "preshave" the gear tooth profile. In both cases, the relation between the number of teeth on the gear to be cut and the appropriate chamfering value varies monotonously and continuously, such that the rate of such variation is relatively large where the number of teeth is relatively small.
In other words, prior hob cutters have been designed to optimally cut a gear having a particular number of teeth. If a gear having more than this particular number of teeth is cut, the chamfer will be increased. On the other hand, if a gear having fewer teeth than this particular number is cut with the same hob cutter, the chamfer will decrease or disappear.
Accordingly, in the prior art, one of several different hob cutters was selected responsive to the number of teeth on the gear to be cut, in order to appropriately chamfer the teeth of the gear.
SUMMARY OF THE INVENTION
It is an object of the present invention to overcome the above-described disadvantages of the prior art and to provide a single hob cutter for cutting involute gears, whereby a range of gears widely varying in number of teeth can all be chamfered properly.
The above-described object can be achieved by a hob cutter according to the present invention, the hob cutter comprising a cutting edge consisting of a first rack tooth profile portion, for cutting a main tooth profile portion, and a second rack tooth profile portion for chamfering an addendum portion, characterized in that the pressure angle .alpha..sub.1 of the first rack tooth profile portion is larger than the pressure angle .alpha..sub.0 of the gear to be cut, that the pressure angle .alpha..sub.2 of the second rack tooth profile portion is larger than the pressure angle .alpha..sub.c at the pitch circle diameter (PCD) of a second involute portion of the gear, i.e., the chamfer, and that the above-mentioned factors are determined according to the following general formula: be cut.
The angles .alpha..sub.2 and .alpha..sub.c are similarly related.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a partial enlarged sectional view of one embodiment of a hob cutter for cutting involute gears according to the present invention, showing the structure of the tooth portion;
FIG. 2 is a partial enlarged sectional view showing comparable example of prior art hob cutters;
FIG. 3 is a graph showing the relation between the number of teeth on the gear to be cut and the appropriate chamfering values (expressed as a function of the module) of the hob cutter according to the present invention (Curve A), and the corresponding relation between the number of teeth and the chamfering values of the prior art hob cutter (Curve B), respectively; and
FIG. 4 is a graph showing the relation between the number of teeth and chamfering values of a gear of module m=4, pressure angle .alpha..sub.0 =20.degree., which is achieved according to the present invention.
PREFERRED EMBODIMENT OF THE INVENTION
In FIG. 1 and FIG. 2, .alpha..sub.1 is the pressure angle of a first rack tooth profile portion of a hob cutter for cutting involute gears according to the present invention, and .alpha..sub.1 ' is the pressure angle of a first rack tooth profile portion of the prior art hob cutter, which in the prior art was equal to .alpha..sub.0, the pressure angle of the gear to be cut. .alpha..sub.2 is the pressure angle of a second rack tooth profile portion in the hob cutter according to the present invention, for cutting the chamfer on the teeth of the gear at an angle .alpha..sub.c, and .alpha..sub.2 ' is the pressure angle of the
REFERENCES:
patent: 3786719 (1974-01-01), Kimura et al.
patent: 4184796 (1980-01-01), Sakai et al.
patent: 4475319 (1984-10-01), Wiry
Hall William D.
Kabushiki Kaisha Technomax Eighty Five
Schmidt Frederick R.
Shideler Blynn
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