| Type |
Precision
Rating |
Features |
Applications |
Comments
Regarding Precision |
| Spur |
excellent |
Parallel shafting
High speeds
and loads
Highest efficiency |
Applicable to all
types of trains and
a wide range of
velocity ratios, |
Simplest tooth elements
offering max -
imum precision. First choice, recom -
mended for all gear meshes, except
where very high speeds and loads or
special features of other types, such as
right - angle drive, cannot be avoided. |
| Helical |
good |
Parallel shafting
Very high speeds
and loads
Efficiency slightly
less than spur mesh |
Most applicable to
high speeds and
loads; also used
wherever spurs
are used. |
Equivalent quality to
spurs except for
complication of helix angle.
Recommended for all high- speed
and high-load meshes. Axial thrust
component must be accommodated. |
Crossed
- helical |
poor
|
Skewed shafting
Point contact
High sliding
low speeds
light load. |
Relatively low
velocity ratio;
low speeds and
light loads only.
Any angle
skew shafts. |
To be avoided for precision
meshes.
Point contact limits capacity and precision.
Suitable for right - angle drives if
A less expensive substitute for bevel
gears. Good lubrication essential because
of point contact and high sliding action. |
Internal
spur |
fair |
Parallel shafts
High speeds
High loads |
Internal drives
requiring high
speeds and high
loads; offers low
sliding and high
stress loading; good
for high capacity,
long tie. Used In
planetary gears to
produce large
reduction ratios. |
Not recommended for precision
meshes
because of design, fabricabon, and
inspection limitations. Should only be
used when internal feature is necessary. |
| Bevel |
fair to
good |
Intersecting
shafts
High speeds
High loads |
Suitable for 1:1 and
higher velocity
ratios and for right-
angle mashes
(and other angles) |
Good choice for right-angle
drive,
particularly low ratios. However,
comptcaled tooth form and fabrication
limits achievement of precision.
Should be located at one of the less
critical meshes of the train. |
Worm
mesh |
fair to
good |
Right - angle
skew shafts
High velocity
ratio
High speeds
and loads
Low efficiency
Most designs
nonreversible |
High velocity ratio
Angular meshes
High loads |
Worm can be made to high
precision,
but worm gear has inherent limitations.
To be considered for average precision
meshes, but can be of high precision with
care. Best choice for combination high
velocity ratio and right- angle drive. High
sliding requires excellent lubrication. |