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 CalculatorFα
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.
ffα
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.
Technical FilesGear TerminologyGear Shop
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.
fHß
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.
ffß
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.
CHα
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.
CHß
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 Calculatorfp
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.
