Bevel gears: straight and spiral

01

Choose straight or spiral teeth by speed and load

KHK's bevel gear guide says “Straight bevel gears are generally used in relatively slow speed applications (less than 2m/s circumferential speed). They are often not used when it is necessary to transmit large forces.”; they are easier to make and their teeth cannot be ground after heat treatment. Spiral bevel gears can be ground after heat treatment, mesh gradually and smoothly, are stronger, and at operating speeds above 10 m/s give markedly lower noise and vibration. [1]

KHK reproduces a textbook view that above about 5 m/s peripheral velocity spiral bevel gears are considered desirable for quiet running. It also notes that “presently most gears use the Gleason method”, and that for spiral bevel gears “in Germany, the Klingelnberg type with equal toe and heel tooth depth is still deeply rooted in use”. [1]

Editorial calculation: a 60 mm reference diameter pinion turning at 1,500 min⁻¹ has a pitch-line speed of π × 0.060 × 1,500 ÷ 60 ≈ 4.7 m/s, already above the 2 m/s range KHK gives for straight bevel gears; at 3,000 min⁻¹ it reaches about 9.4 m/s.

Give the supplier the power or torque, input speed, ratio, shaft angle, rotation directions and which shaft drives, duty and shock, required accuracy and noise, lubrication, space for the pair, and whether teeth must be ground after hardening.

02

Fix the Gleason geometry and face width

KHK's technical reference gives Gleason tooth proportions: straight bevel gears have tooth depth 2.188m with working depth 2.000m, while Gleason spiral bevel gears are a stub system with tooth depth 1.888m and working depth 1.700m, applicable to modules above 2.1. In the Gleason straight system the pinion is positively and the gear negatively profile-shifted to balance strength. [2]

KHK's worked spiral bevel example uses module 3, 20° normal pressure angle, 35° mean spiral angle and 20 (left-hand) and 40 (right-hand) teeth, giving reference diameters of 60 and 120 mm, cone angles of 26.565° and 63.435° and a cone distance of 67.08 mm; face width should be less than 0.3R or 10m, and 20 mm is used. Its straight bevel example with the same teeth limits face width to R/3 and uses 22 mm. [2]

KHK notes that the straight bevel gear with Gleason crowning (Coniflex) tolerates poor tooth contact from improper mounting and assembly, and that its spiral bevel equations apply only to Gleason Spread Blade or Single Side cutting; gears cut by another method need different equations. [2]

03

Plan the spiral hand, rotation and thrust

Gear Solutions' technical column explains that a spiral bevel pair only runs with one gear, “typically the pinion”, left-handed and the mating gear right-handed. The pinion's thrust can point either way depending on rotation and whether it drives or is driven, while the gear's thrust always tends to pull it out of mesh. [3]

The same column notes that in a straight bevel pair the axial force on one gear equals the radial force on its mate, while in a spiral pair rotation and spiral hand both set the axial loads. Reversing rotation swaps which tooth faces mesh; if thrust bearings exist only on the hub side, reversing will cause premature wear, so bearing location and size must account for both directions. [4] KHK likewise lists the change of thrust direction with rotation and twist angle as a disadvantage of spiral bevel gears. [1]

04

Compare what suppliers offer

Suppliers linked to this page list bevel gears; each card links to the page reviewed.

Listings include straight, spiral and miter bevel gears made to drawing, alongside spur, helical and worm gears, sprockets and gearboxes. Ask each supplier whether the pair is cut to the Gleason or Klingelnberg system, whether teeth are ground or lapped after hardening, and for a tooth contact pattern report.

05

Trace the gear pair

This is a functional reference built from the sources cited; it is not one maker's specification.

06

Fill the specification fields with values for your pair

A bevel gear quotation needs values for your drive. The table explains each field, gives published values where a reviewed source states them, and says what to obtain from the supplier.

07

Send the drive, geometry and mounting data together

Paste it into your enquiry below or into an email to a maker, then replace every bracket.

Drive: [power or torque; speed; ratio; which shaft drives]
Rotation: [directions; reversing or not]
Type: [straight; spiral; Zerol; miter]
Geometry: [module; teeth; spiral angle and hand; face width]
Finish: [material; hardening; grinding or lapping; accuracy]
Mounting: [shaft angle; mounting distances; bearing positions]

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