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Choosing a hollow shaft gearbox: worm or bevel gear?

What is the right hollow shaft gearbox for me? This is a frequently asked question by (new) customers of Apex Dynamics. In order to make a good choice, there are two important questions to answer. In practice, people often make a choice between a bevel gearbox and a worm gear gearbox (We will not consider the hypoid variant in this article). We also discuss these considerations in this article so that you can make a clear choice yourself.

Choice of a hollow shaft gearbox

At Apex Dynamics often the question comes up: “We want a hollow shaft gearbox, which one should I choose? This is a logical question in itself, but to make a good choice we need more data. In fact, only 2 questions are needed to determine the right series. There are 2 criteria when determining the type of hollow shaft:

Should the hollow shaft be continuous or not?
Must the hollow shaft be form- or force-locked?

Continuous thru hollow shaft

A hollow shaft does not have to be continuous, it can also end with a clamping ring in a shaft stub. If you want it to be continuous, the outgoing stage of the gearbox is always right-angle. As can be seen from the table below, on the basis of this choice, half of the options is already eliminated.

Hollow shaft form- or force-locked

The characteristic of a force connection is that if the force that presses the parts to be connected together is lost, the connection is no longer secured. In other words, the parts are joined together by clamping, pressing or shrinking. This transmission is always free of backlash or play. A well-known example of this is the handbrake of a car or a wedge under a door.

The opposite of force-closed is form-locked. The force is then transferred through the shape of the driven and to-be-driven object. Well-known examples of this are, for example, riveting and keyways. Especially with keyways there can be a little backlash or play.

Other considerations

What is also interesting: How much backlash or play is allowed and is the hollow shaft used for the passage of cables or others?

Hollow shaft gearboxes overview

In the table below an overview of the possibilities within the Apex Dynamics program :

	AT-FH	AT-FC	KH	KF-S4	AFH-S4	AD + attachment	AH + attachment	PD + attachment
Description	Through-hole hollow shaft with keyway	Through-hole hollow shaft with shrinkdisc	Through-hole hollow shaft with output flange	Through-hole hollow shaft with shrinkdisc	Blind through-hole hollow shaft with shrinkdisc	Blind through-hole hollow shaft with shrinkdisc	Blind through-hole hollow shaft with shrinkdisc	Blind through-hole hollow shaft with shrinkdisc
Execution	Right-angle	Right-angle	Right-angle	Right-angle	Right-angle or straight	Right-angle or straight	Right-angle or straight	Right-angle or straight
Dynamics	Less due to the limitation of the keyway	Good	Very good	Good	Good (Limitation is the single shrinkdisc)	Good (Limitation is the single shrinkdisc)	Good (Limitation is the single shrinkdisc)	Good (Limitation is the single shrinkdisc)
Torque density	Less due to the limitation of the keyway	Good with 2 shrinkdiscs	Very good	Good with 2 shrinkdiscs	Good	Good	Good	Good
Nominal torque ti;;	3.200 Nm	3.200 Nm	1.800 Nm	1.800 Nm	3.800 Nm	2.000 Nm	10.915 Nm	228 Nm
Backlash	<6 arcminutes	<6 arcminutes	<3 arcminutes	<3 arcminutes	<1 arcminutes	<1 arcminutes	<1 arcminutes	<6 arcminutes
Ratio’s	1:1 tot500:1	1:1 till 500:1	3:1 till 100:1	3:1 till 100:1	3:1 till 1.000:1	3:1 till 100:1	3:1 till 100:1	3:1 till 100:1
Form- or force locked	Form	Force	Form	Force	Force	Force	Force	Force
Delivery time	2-3	2-3	3-4	3-4	4-5	2-3	4-5	2-3
Material housing	Stainless or blackened steel	Stainless or blackened steel	Steel	Steel	Steel	Stainless	Steel	Steel
Monting with reaction arm	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes
Efficiency	High	High	High	High	High	High	High	High
Execution	Bevel gear, possibly with planetary pre-stage	Bevel gear, possibly with planetary pre-stage	Hypoïd, possibly with planetary pre-stage	Hypoïd, possibly with planetary pre-stage	Planetary, possibly with hypoid pre-stage	Planetary, possibly with bevel gear pre-stage	Planetary, possibly with hypoid pre-stage	Planetary, possibly with bevel gear pre-stage

Worm and bevel gear gearbox comparison

Apex Dynamics has no worm gearboxes in its program. In our opinion, the low efficiency in combination with the relatively expensive (servo) drive is not an optimal combination. In practice it is often a bit strange. You generally choose a servo motor for accurate positioning, otherwise you could just use a three-phase motor with encoder feedback. At the same time, we see that often a more powerful (i.e. more expensive) servomotor and driver must be used to compensate for the poor efficiency. In other words, the combination of a servo motor and a worm gearbox is NOT logical. It is often more interesting to choose a bevel gear gearbox.

The main considerations for choosing a worm gear or bevel gear gearbox:

Friction and wear – The gears in a bevel gearbox roll over each other, so there is less friction and therefore a higher efficiency. The gears of a worm gear slide over each other, causing friction and wear.
Purchase price – A worm gearbox is in many cases cheaper to produce and therefore usually has a lower purchase price than a bevel gear gearbox.
A worm gearbox can have a degree of self-locking. However, this is not allowed regarding the CE directive, which requires a separate mechanical brake.
Accuracy, a bevel gearbox has a low, permanent backlash. The backlash of a worm gearbox increases freely due to the friction and is adjustable in some cases.
Efficiency – The efficiency of a worm gearbox with a large transmission ratio is approximately 50%, a bevel gear gearbox has an efficiency of >90% in a comparable situation.

Which hollow shaft gearbox is best for your application?
We are happy to help you making this choice. We share our knowledge and experience with comparable applications so that you know exactly what the impact of this choice is on the rest of your application or, for example, maintenance and efficiency.