Foxwood Industrial Park, Sheepbridge, Chesterfield S41 9RN
+44 (0)1246 455500
sales@ondrives.com

Gear Metrology

Profile (Involute) Deviations

Typically measured on 4 evenly spaced teeth or gaps. Left and right flank measured for each tooth or gap over the usable length LAF. Analysis region Lα is typically 92% of the active length LAE.

example Gear Calculator

Fα

Total Profile Deviation

Distance between the highest and lowest points on the profile trace within the analysis region Lα measured perpendicular to a zero-error reference line. When working to ISO or DIN standards any high point in the region from end of Lα to end of LAE is included.

fHα

Profile Slope Deviation

Positive or negative deviation of a best-fit reference line through the profile trace. Measured perpendicular to the start point of a zero-error reference line over the analysis region Lα. When given the symbol fHα’ the value is from the reference lines over the active length LAE.

f

Profile Form Deviation

Distance between the highest and lowest reference lines that touch the profile trace and are parallel to the best-fit reference line. Measured perpendictular to a zero-error line. when working to ISO or DIN standards any high point in the region from end of Lα to end of LAE is included.

Lead (Helix) Deviations

Typically measured on 4 evenly spaced teeth or gaps. Left and right flank measured for each tooth or gap. Analysis region Lß is typically 80% of the gear face width b.

exampleGear Calculator

Fß

Total Lead Deviation

Distance between the highest and lowest points on the flank trace within the analysis region Lß measured perpendicular to a zero-error reference line. When working to ISO or DIN standards any high point outside of the analysis region is included.

f

Lead Slope Deviation

Positive or negative deviation of a best-fit reference line through the flank trace. Measured perpendicular to the start point of a zero-error reference line over the analysis region. When given the symbol fHß’ the value is from the reference lines over the full face width of the gear.

f

Lead Form Deviation

Distance between the highest and lowest reference lines that touch the flank trace and are parallel to the best-fit reference line. Measured perpendicular to a zero-error reference line. When working to ISO or DIN standards any high point outside of the analysis region is included. 

Profile Modifications

Typically used to compensate for tooth deflection under load and influence load and transmission error TE of gear systems. Modifications can be the same or different on left and right flanks.

Cα

Crowning

Increasing reliefs of the tranverse tooth profile from a point typically central over the usable profile length LAF, in an arc like progression.

fKo

Tip and Rooth Relief

Increasing reliefs of the transverse tooth profile either from the tip, tip form diameter or root form diameter. Can be linear, arc like or parabolic in shape.

C

Pressure Angle Modification

A linear relief is applied over the full length of the usable profile length LAF. As per ISO 21771 a positive value removes material at the tip and increases the effective pressure angle.

Lead Modifications

Typically used to compensate for system deflection and influance load distribution over the face width of the gear.

Cß

Lead Crowning

Constantly increasing relief of the flank line in an arc like progression. Typically central over the face width of the gear.

CßTop CßBottom

Lead End Relief

Contantly increasing relief of the flank line applied over a short distance at one or both ends of the face width of the gear. Can be linear, arc like or parabolic in shape.

C

Lead Slope Modification

Constantly increasing relief of the flank line applied over the full face width of the gear. It is not necessarily linear.

Pitch Deviations

Measured in tooth gaps left flank pitch and right flank pitch.

example Gear Calculator

fp

Single Adjacent Pitch Deviation

Adjacent pitch error is the difference between the actual and nominal individual circular pitches in the transverse section of a right or left flank.

Fu

Difference of Successive Pitches

Difference between successive actual individual circular pitches in the transverse section of a right flank (RF) or left flank (LF).

Fp  Fpz/8

Cumulative Circular Pitch Deviations.

Fp Cumulative circular pitch erros from the accumulating summation of adjacent pitch errors fp.
Fpz/8 Largest cumulative circular pitch error over ≈ z/8 pitches.

Fr

Radial Runout

From gear axis this is the range of radial positional deviation of all the tooth gaps. Defined by a ball in all tooth gaps.

Tooth Thickness

Tooth thickness is measured over physical teeth but our gear inspection machines are also able to measure tooth spaces on request.

Mdk MdR

Mdk = over two rollers  MdR = over two balls

Distance over two balls or rollers of diameter Dm sat in a tooth gaps at, or as close to, 180 degrees as possible.

sn

Tooth Thickness

Circular tooth thickness in normal section at reference diameter d.

Wk

Base Tangent (Span)

Base tangent (span) over k number of teeth. Linear distance in normal section over k number of teeth which is tangent, or as close as possible, to the cylinder formed by base daimeter db. For an internal gear k is number of gaps.

da df

Tip and Root Diameter

Measured da tip diameter and the df root diameter.

z  -z

z = number of external teeth. eg. 20z = 20 external teeth.
-z = number of internal teeth. eg. -60z = 60 internal teeth.