Slope modification?

[[Ed...]]

Hi, my friends.

I have this kind of demand in drawing:

I`m little bit confused about what I need to put in calculation of fHbeta? Is this correct, nominal value, slope modification, will it calculate correctly high point of crowning?

And what is this FhbetaC?

Edited December 12, 2025

[[Ro...]]

Hi,

fHbetaC (also fHalphaC) is defined in ISO 1328-1:2013-09. 
Sorry, I´m not allowed to share screenshots from standards, but if you have the ISO 1328-1:2013-09 have look into page 34 B.3.3. and formula B.2
A very good picture example is included in VDI/VDE 2612 Part 1:2024-12 on page 38.

In the user manual of GEAR PRO you can search for "Nominal slope modification for profile and line".
The topic is described very clearly there ...

[[Ky...]]

If I am reading this correctly, it almost looks like the left and right flanks have slightly different slopes. The tolerance for FHbeta is 18 microns, but on the left flank, you have to give it a nominal offset of -32. I couldn't tell you the reason for the specification, but without further information, that's probably be my interpretation.

[[Ed...]]

Unfortunately I don`t have user manual like you

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 maybe because I have older version.

But in this example I need to use Nominal value (-0,032 fHbeta)? Do I need to use it in Slope modification?

Like I understood, I need to put it in Nominal value, but what kind of examples are when to use Slope modification? 

[[Ro...]]

It is really depening from your usecase.
If a drawing defines "slope modification" as it is defined, you have to use it in the field "slope modification". 
The helix line on the printout will be corrected by this value.
The deviation fHbeta is defined to be the deviation from the nominal value (per definition from the nomial value of slope modification).
But there exists other software solutions which are not (or were not) capable to define slope modification as a nominal value.
In those cases the "workaround" is/was to define it as a "nominal shift" of fHbeta (which is in my personal opinion not correct).
To be comparable, GEAR PRO also has the possibility to set a nominal value for fHbeta.
In this case, the helix line on the printout will not be corrected, only the calculated deviation fHbeta will include the nominal value.
The tolerance in that example is -32 µm +/- 18 µm instead of ...
... slope modification per definition cHbeta = -32 µm with fHbeta tolerance of +/- 18 µm.
I hope this is better understandable?

[[Ed...]]

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Great! Thank you 🙂