1.10 Tooth profile modification
Tooth profile modification

Regarding Tooth profile modification, modify thetooth profile that is shifted from the involute to be(concave) near part of tooth tip or fillet of dedendum.
Tooth profile modification is to prevent deflectionof tooth caused by load, intereference of Tooth
tip caused by Pitch deviation and adds to provide
smooth gear rotation.
However, needlessly exceeding amount of Tooth profile modification is not advisable as it will result in deterioration of Contact ratio. Proper amount of Tooth
profile modification is highly recommended.
Commonly, modify the fillet area of dedendum fordriver gear and area of Tooth tip for driven gear.

Modification of Tooth trace(Crowning and Relieving)

Refer to Fig. 33, regarding modification of Crowning.
Reduce Tooth thickness from centre towards the endof Tooth trace gradually.
Refer to Fig. 34, regarding Relieving. Reduce Tooth
thickness gradually at end of Tooth trace.
The purposes of both modifications are to preventthe stress concentration by single contact. Different points between Crowning and Relieving are that
Crowning prevents stress concentration caused bysingle contact and Relieving simply relieves the endof Tooth trace to prevent single contact.
These methods are commonly called Tooth tracemodification. Excessive amount of Tooth trace modification will result in deterioration of tooth contact.
This excessive modification is not advisable.

Modiﬁcation
amountFig. 32 Profile modification(Part of Tooth tip of driven gear)

Fig. 33 Crowning

Fig. 34 Relieving

40Topping and Semi Topping

When cutting the flanks by Topping hob cutter, theoutside diameter of gear is also processed at thesame time. Semi topping method is similar but outside diameter is chamfered by hob cutter.
Method of Topping uses an external micrometer tomeasure the outside diameter to control Tooth thickness if module is too small and unable to use methodof Sector span.
Topping cutter is designed to obtain designatedTooth thickness when machined outer diameter ofgear is in place. It has an effect to reduce off-centre
deviation of outside diameter as the hob cutter processes the outside diameter of gear at same time.
Semi topping prevents dent marks and burrs fromoccurring at Tooth tip. Semi topping has an effect tolower oscillation and noise, as smaller dent mark doesnot interfere with engagement. Excessive Semi topping will deteriorate Contact ratio and is not advisable.

Straight adjustment

Tooth profile adjustment

Process of hob cutter slightly cuts away both endsof fillet from outside diameter of gear in directionof Tooth trace. There are types of Straight line andCurved line profile adjustments, which can reduce
the fluctuation of spring constant for gear. This has aneffect to lower oscillation and noise to within expectation.
Professor Niemann has introduced other adjustments,
where the outside diameter of gear is slightly (in other words, not as extreme as for Bevel gear) tapered or
the outside diameter of gear is cut in an arc shape tomake it a drum shaped body, which is not outlined
here.
Another method is for outside diameter of Bevel gear
to be slightly cut away to prevent interference at thetoe.

Arc adjustment

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