Page 188 - Gear Technology Solutions

represents all basic settings required for positioning the inside blade part of the
interlocking cutter head. The direction and length of vector RWOB defines the
length and direction of the vector EXOB which represents all basic settings required
for positioning the outside blade part of the interlocking cutter head. The magni-
tude and angular orientation of the difference vector DEX between the inside blade
cutter center and the outside blade cutter center is a sufficient definition for the set-
up of the imbedded double spindle arrangement of the cutting machine.

If the convex flanks and the concave flanks of the coupling are cut in a completing
cycle, then the blades have to be spaced equally as shown in Figure 2 in order to
achieve the required constant slot width and tooth thickness taper. The blade point
radii have to be adjusted, such that the radius of the inside blades and the radius
of the outside blades are equal at the reference point (point between blade ad-
dendum and blade dedendum). Small deviations from this rule can be applied to
control both tooth thickness and backlash. These required adjustments lead to two
conflicts.

13.2 Conflict No. 1 - How to Generate Length Crowning?

Certain amounts of length crowning are required for most cases of coupling gears.
Length crowning can be achieved by changing the blade point radii (larger outside
blade radius and smaller inside blade radius) or by applying cutter head tilt. In the
completing process, both flanks of one slot are cut with the same cutter (contain-
ing inside and outside blades) and with the same machine settings. A change of
the blade point radii would also change the slot width, which is not permissible.
Using a cutter head tilt to achieve length crowning will require large amounts of tilt
o
o
because of the small pressure angles found in couplings (5 to 15 is common).
Large amounts of cutter head tilt will reduce the clearance gap and most likely
lead to gear face mutilations.

13.3 Conflict No. 2 - Length Crowning causes Spiral Angle Error

The cutter head inclination to the dedendum angle will cause flank form deviations
in the form of spiral angle errors which will not cancel out between the two cou-
pling members. If the coupling members are cut in a completing process, there will
then be no geometric or kinematic freedoms available to eliminate the mismatch
between the two members.

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