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History of the Bevel gear

As experts we sometimes assume that everyone understands us when we talk about certain terminology. We found out that not everyone knows what a planetary gear or bevel gear is. Therefore we are going deeper into right-angle gearboxes in this article. We will inform you about the history, technology and talk about how gearboxes change movement directions.

Apply gears

Using gears is one of the oldest ways to drive movement, change of speed or direction. There are constructions found from the time of the ancient Greeks (150 before Chr.) that simulated the course of the moon and planets.

Much better known are the antique drives that were used a lot in (wind) mills. A spur gear is a gear which is equipped with wooden pegs. The wooden pins can be replaced when worn out with new pins, so the life of the drive can be extended. This type of wooden right-angle cage gears are almost no longer used, it has been overtaken by technological developments. Today we know gears in all shapes, sizes and materials.

When choosing which bevel gear?

The right-angle gearbox is applied to lead a rotary motion at right angles, but which right-angle gearbox is the best for a specific application? What are the individual characteristics and what are the pitfalls? What is the efficiency of right-angle gears and which bevel gear is best suited in servo technology?

The reasons to use a right-angle gear unit are:

• Space saving; as a motor with gearbox builds too long.
• If you want a gearbox with hollow shaft, to feed a shaft or cables.
• In the event of shaft mounted gearbox benefits.
• Etc.

Here is a brief summary of the different types of existing right-angle gears, with their specific characteristics:

Bevel gears (Dutch: Kegelvormige tandwielen, German: Kegelrad)

These bevel gears are used to transmit rotational motion at right angles, whereby the two axis of the gears intersect. This type of gear is therefore often built symmetrically. The movement consists of rolling without sliding of two bevels, hence the name. The gears with spur (Dutch: rechte, German: gerade Verzahnung) or spiral teeth (Dutch: Spiraal, German: Spiralverzahnt) are used.

Hypoid gears (Dutch: Hypoïde, German: hypoid)

Hypoid gears are special bevel gears wherein the axis of the gears are offset. They are used, for example, in cars and fork-lift trucks to bring the rotation of the drive shaft on the rear axle and thus to drive the wheels. With this principle, the toothing is always spiral (helical).

Worm and worm wheel gears (Dutch: Wormwiel, German: Schneckenrad)

A worm and worm wheel are considered as gears. If the “worm” (a spiral gear) is driven, the worm wheel will rotate slowly (for example, one tooth per revolution of the worm), but with a high torque.

Due to the nature of this high speed reduction (high torque increase), this system cannot be used in reverse unless a non-standard high-lead (low reduction ratio) is used. Such a system is typically used in garage doors, the motor is connected to the worm and worm wheel to the port, the port does not go down when the engine fails. The disadvantage is therefore perfectly usable as an advantage in certain setups that for instance are self-secured.

Other:

In addition to these more ‘standard’ right-angle transmissions there are countless more “exotic” right-angle gears which we will not describe in this article.

Technical characteristics and differ by type:

	Cage gear	Bevel gear	Hypoid	Worm wheel
Ratio of	1 : 10	1 : 1	1 : 3	1 : 5
to (ca.)	1 : 200	1 : 5	1 : 10	1 : 100
Backlash (ca.)	2 ~ 5°	< 6″	< 4″	< 6″
Power density	—	++	+	++
Efficiency	~60%	~95%	~95%	~70%
Noise	—	++	+	++
S1 use	yes	+	++	++
S5 use	no	++	++	no
Dynamic behaviour	no	++	++	–
Available as gearbox	No	yes	yes	yes
Inertia	–	++	++	–
Lifespan	–	++	++	+

Of course, manufacturers of servo gearboxes do not have the “antique” cage gear in their program. The worm gear has the advantage that it can easily be made low backlash at a high ratio and is inexpensive, however, the disadvantage is the poor efficiency: approximately 70%. Because of this poor efficiency the servomotor has to be heavier to compensate for this loss. And also the servo amplifier or frequency converter has often to be forced cooled. Eventually, the drive can be much more expensive than estimated initially. And in S5 operation, the wear of the teeth is often too large.

The intended benefit of self-locking ability is void in the eyes of CE: Since a gear unit must not be seen as self-locking in the event this could cause personal injury or other danger.

Apex Dynamics, supplier of servo gearboxes, has in its delivery program for right-angle variations the choice of bevel gearboxes and hypoid gearboxes, whether or not fitted with a front or end planetary stage. Obviously, with a low backlash and low inertia for dynamic applications!

For more information on this topic, please contact us.