Why are bevel gears so expensive?

The choice between Worm gear units and bevel gear units has a major influence on efficiency and operating costs. In this article we would like to give you the most important advantages of worm and bevel gear units so that you can determine which one is the most suitable for your application. If you still have any questions, please do not hesitate to contact us: Contact form

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Further information on worm and bevel gear units.

Frequent applications of angular gearboxes

Worm and bevel gears are often used to transmit motion at right angles or when other properties are required.

• Conveyor belts
• Crane
• Elevators
• Mixer
• Beverage industry
• Many other applications

Worm gear

Worm gears. Image source: © roostler – Fotolia. com

A worm gear unit consists of two parts: a worm shaft with worm gears and a worm wheel. The two components are often made of two different materials (steel worm shaft and bronze worm wheel). Worm gears transmit the movement force at right angles via a sliding effect instead of a rolling movement.

Advantages

• Worm gears are mainly used when a large gear ratio is required. With a worm gear unit, a large overall ratio can be achieved with only a few stages. This means that a smaller, less expensive gearbox can be used.
• The highest ratio of a worm gear unit is about 100:1.
• High self-locking due to the sliding effect of the worm shaft makes an additional brake either obsolete or it is only necessary to install a small, less expensive brake. However, this property depends on the angle of inclination and the friction angle.
• More favourable than bevel gear
• Hollow shaft possible

Schematic diagram of a worm gear unit

Disadvantages

• The sliding contact of the gears causes strong friction, which results:
  • one High operating temperature
  • one Low efficiency
• High wear on the worm wheel, which is mostly made of bronze. (Only through bronze production a relative efficiency is possible. The friction would be much higher with steel on steel.)

Bevel gears

4 types of bevel gears

• Spiral
• Straight
• Cerol
• Skew Tooth

Bevel gear sets are composed of two parts, the bevel pinion and bevel gear, which transmit movements at right angles.

For more information, please visit Spiral Bevel Gear.

Bevel gears use angular gear teeth. As the gears rotate, the entire tooth width of the interlocking teeth is used to transmit the force. In addition, several teeth interlock at the same time. This results in the following advantages.

Advantages

• Quiet Operating noise (Quiet operation is particularly advantageous in environments such as theatres or airports.)
• Increased torque capacity compared to worm gears of the same size.
• High efficiency (rolling of bevel gears is very efficient compared to the sliding effect of worm gears (98.5%). The metal bevel gear teeth never come into direct contact with an oil film.)
• Hollow shaft possible

Bevel gearbox with 1:1 ratio. Image source: © roostler – Fotolia.com

Disadvantages

• High costs.
• Bevel gears are manufactured in pairs. For maintenance and repair, both gears must be replaced.
• In order to achieve high efficiency, bevel gear sets must be positioned exactly, so the shafts must be adjusted very precisely.
• Limited translation range. Maximum ratio of 6:1 per bevel gear set. Spur gear stages are necessary in order to achieve a higher overall gear ratio.
• Bevel gears are not recommended for high-speed reduction. At high speed, a bevel gear unit generates noise.

Further information

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Comments

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Rick Rowlands,
Not to rain on your parade, but further to Forrest's post:

Spiral bevel blanks have different face & root angles than straight or Zerol bevel gears.
As For the calc's it's called a "machine summary" this has to be done first before the drawing change, because this is where the numbers come from.

The straight gear cutters are relatively simple compared to Zerol & spiral cutters.
Three Diametral Pitch cutters are probably going to be 12.00" Diameter heads so, if the gear shop has the cutter heads (about $8,000.00 each 1990's) the blade and shim sets, one for the gear & two sets for the pinion say $6,000.00 a set, used to be 12 weeks delivery, You are all ready into a big number.

Machine tooling, nose arbor for each part both for the cutting machine and the test machine, these are some moderately big parts so the arbors are going to be big too, cutting machine needs custom draw rods for the hydraulic chucking system on "Gleason" machines.

Now you go to heat treat and you hope the gear house engineer has enough experience to accurately guesstimate how the spiral is going to unwind, so that your gears finish up with the correct contact pattern. Drwg difficult to read, is that Rc 30? If so I would have rough blanked, NQ&T to Rc 30, finished machined & then finished cut the gear teeth.

I had many one off quotes & did not see the customer proceed, some that did I ground the parts from the solid, takes a while grinding, but you did save overall for one or two parts versus the cutter cost, you still have arbor costs, also gear house will probably need at least one set of parts for setup & development, usually do not need for straights.

I wish you well in your endeavor,

Les H.

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