Profile Modification vs. Profile Shift

[[Ma...]]

I am working with an internal helical gear for the first time and the term "Amount of Profile Modification" is on the print that I have not seen before.
It says Pressure Angle (Mean Value): Nominal = -16.5µm ±12.5 (Right Surface); Nominal = -12.5µ ±12.5 (Left Surface)
Pressure Angle (MAX-MIN); 25.0µm MAX

Is this the same as Profile Shift?
Are there settings in GearPro to include this modification?
Can anybody shed any light on this?

Any help would be much appreciated.
Marc

[[Ch...]]

Marc,

Howdy. I have a lot of gear knowledge and experience. I've seen some unique ones in my days ..

This does not make a lot of sense however. I've worked with internal helical gears and splines.

Pressure Angle is typically a Basic dimension is not typically measured. Measurement of the involute profile will give you an idea of what your pressure angle is. I believe the values with the tolerances for L + R surfaces in your post must be the fha/helix/Lead tolerances.

Profile modification = any modification from a true involute form ( or a straight line trace result from gear pro - provided you've enter correct nominal geometry)

Profile shift = is a unique one and I've only seen a few times. It's a bit much to explain unless you're familiar with gears and addendum shift. instead of a ratio that enlarges or shrink an entire tooth, profile shift just essentially modifies tooth thickness (+profile) and does not change addendum/dedendum or tooth height (proportional change).

Can you share a copy of the gear data block ?

Thanks,

[[Ma...]]

Thank you Chris for the reply.
I have a little understanding of Profile Shift but never heard the term Profile Modification before and thought they might be different.

I think I understand that if the L or R surface is moved in a + or - direction it would make the thickness of the tooth thicker or thinner and change the actual pressure angle value, though I wouldn't know how or if it could be measured or if this is even a correct statement. 😕

The information in the original post is directly from a "Accuracy Table for Tooth Surface of Involute Helical Gear" table with specified value in (µm)
Here is the Helical Gear Table

[[Ch...]]

Marc,

Got it. Thanks, this table looks fairly straightforward.

What I forgot to mention above, is I do not believe Gear Pro has "Profile Shift" options, as far as I've seen.

I do not see the analytical tolerances here straight away, or Spec/Class listed.

Helix hand and angle are clearly specified. As you may be familiar - with helical gearing, there is a normal and transverse plane, one is a plane that is parallel to datum axis, the other is parallel to the helix angle,

We may need to see the profile modification note/chart if possible, black out any important info ,etc.

They mention semi-topping : Is this internal gear hobbed ? Seems fit for grinding - hobbing is possible however.

Does Eng Dept have any input ? Is there a spec listed AGMA/ DIN /ISO ?

Thanks,

[[Ro...]]

Marc, as Chris already mentioned please share the modification chart, than we can suggest a way how to define the GEAR PRO program.
For me your first statement sounds also crazy.
Typically a profile modification can be realized by several modifications.
Also crowning and reliefs are modifications.
Another is typical modification is the profile slope modification cHa (respective in helix direction cHb).
An alternative way to realize a slope modification is to define different alpha or beta angles for left and right flank.
Typically used for conical corrected gears.

[[Ma...]]

Here is the table that I got the information from.
Like I said, this is new to me so I do appreciate you guys taking a look at this and any guidance is appreciated.

[[Ch...]]

Well,

I will say I've never seen anything quite like this before.

Questions :

1.) When they say (for 1 Gear) - is there more than one gear on this part ?


Thoughts:
1.) As mentioned before Pressure Angle is not typically measured or toleranced. I've seen a few rare examples where someone wants an 'actual' value.
2.) If values are in microns as the table says, I'm not sure these 'pressure angle' values make sense, those should be degrees.
3.) I would have to roughly to interpret this P.A. Max-Min = 25.0 max as basic no tolerance. The nominal values and tolerances above must be the toe profile shift from the 25° P.A. standard involute. It appears similar to a tooth thickness correction (reduction in this case), but is not distributed evenly - (L surface has a bit more material than R Surface)
4.) I think I see a way this may be done with a K-Chart in Gear Pro. Enter 25° for P.A. - in profile choose K-Chart. Lower tolerance line will be the nominal values - because the tolerances are all plus(+). The Upper tolerance will be the + tol value in the block. [ For example R Surface Low Value would be -.0165 mm , top line value is -.004 mm, L Surface is : Btm line tol = -.0125mm, top line band is 0.000 mm.
5.) There is also a "tooth crowning" tolerance probably to ensure the profile is straight and doesn't become too curved or "full".
For this just specify the .010 mm for Cß)
6.) For the helix - tooth trace modification -- I think they have these values swapped in Min-Max and Mean value as above with the profile. So 34.0 appears to be the helix 'angle' in decimal degrees However the values from the gear data block in the previous post does not match up (20° N.P.A. & 25° RH Helix). I would double check this with Engineering unless there are 2 gears on this part. -- Going by this latest table I would use use the 34° as the helix angle in the basic data, however we would need to know the hand or direction. 34.0 Max does not sound like a tolerance in microns, as it is specified just above at +25.0 µm, so from nominal helix, I think you could use another K-Chart similar to the profile Lower line would be nominal value and tolerance is all plus material 0.025mm.
Tooth trace unevenness is referring to form. However the 2 options that come to mind are not available in Gear Pro, one of them might be in the latest version. Since it is all (-) form error, they are probably concerned about "hollows" or valleys/voids in the form. The latest version of gear pro might have 'fho' (helix hollows) for lead, they did add one for profile a way back. The other would be an irregularity tolerance which is only available on Gleason GMS as far as I know.

7.) Once you get the correct P.A. and Helix angle, run a helix and profile test on one tooth both flanks and see if you can share what that looks like, we may be able to help further.

8.) Was this gear manufactured in house? Typically the hobber/machinist may have some info, or the Engineer.

Good luck, let us know how you make out...

Happy holidays !

[[Ch...]]

Regarding if Gear Pro can handle this - I would ask Mr. Roman Gross.

From what I can gather ; it may not be able to, due to the profile shift or essentially the 'tooth thickness offset from CL'.

When Gear Pro finds the tooth or gap, whether one flank or two, I believe it assumes the thickness is symmetrical/even. This may produce inaccurate results in this case of different nominal profiles.

There is the 'design' profile and lead which may help - I would like to hear from Roman on this. From the manual - it appears the slope and characteristics will be reported from the input design profile, however I'm not 100% sure that it will account for the different nominal start offsets(shift) for each flank.

I suppose if he says it will not work - we could always get creative, make one .gear file with the left flank nominal "tooth thickness - profile shift", and feed in only on that flank, measure 4 teeth lead and profile on the flank only ,and make another .gear file for right flank.

Regarding pitch - is there a tolerance on pitch/index ? I'm sure we could come up with something for that as well.

Again, good luck. Hopefully Engineering team can help as well.

-Chris

[[Ch...]]

Further insight ...

Just realized while it seems the nominal profile may be -16.5µm, these could actually be min / max values ; i.e. -.0165 / .0125 tolerances, This could be band as well, this would not really account for the profile 'shift' you mentioned however ; just slightly different tolerances per flank (drive/coast, etc.).

I would get some more input from Engineering or Customer, etc.

Good luck !

[[Ma...]]

So, I created 2 profile characteristics one for left flank and one for right and I did try playing with the Design Profile and K-Chart basically shifting the nominal for the profile and didn't see any change in results when running without.

Interestingly, I got some before and after modification results from the company that cut this for us. (non Zeiss equipment)
For Profile tolerances:
They added for the Left flank: -12.5 ±12.5 to the fHa, 25 MAX to the Fa and the ±10 to the Ca
They added for the Right flank: -16.5 ±12.5 to the fHa, 25 MAX to the Fa and the ±10 to the Ca

They did similar for the Lead tolerances from the table.
The only change I see in the results is the Total Profile and Total Lead changed with these tolerances applied.
I just don't know what they did to apply it. Simply adding the tolerance to the characteristic doesn't do it.

The engineer involved with this is unfamiliar with it too. I believe he has been in discussions with them about this, but I haven't heard anything from him yet.

[[Ch...]]

Marc,

Thank for the update. Well it looks like the interpreted the +_.010 as ± .010 hmm, wouldn't have guessed that.

I think it's strange Engineer/Drafter would need an underscore ...

The Ca I wouldn't agree with. In the data block it says "no convex" allowed, so I dont think ± .010 sounds right.

Can you share any charts with us - proprietary info covered of course.

This is very interesting, and certainly not what I was expecting.

Was this other company a 'gear' shop ?

[[Ma...]]

Yeah I noticed that too. It is suppose to be ±.
Sorry I didn't clarify that. The engineer typed that up from the table because he didn't want me sharing any of it and got it wrong. 🙄

The other company is a gear shop, so I would think they know what they're doing.
I have no communications with them. I've asked the engineer to try to get some info from them or the customer and I'm still waiting to hear back.

[[Ro...]]

Gentlemen,
the table looks strange to me, too.
I never saw a definition like this.
However with the answer that you got different measurement results from the manufacturer I assume that it is a slope modification.
If it is defined acc. to VDI/VDE 2612 par 1:2018-11, you can define this with GEAR PRO also.
An alternative method and also common practise in the past is to offset the slope deviation tolerances.
The results as PDF from the measurements of the gear manufacturer can help to clarify how they defined it.
For playing with your actuals the .act from your measurement can help.
Or is this issue already clarified?