CNC: Deviations from the nominal thread profile due to tilting angle of the cutting insert?

[FranzS]

TL;DR Summary

Deviations from the nominal thread profile due to tilting angle of the cutting insert?

Hello CNC experts!
For threads with a high "pitch to diameter ratio", so to speak, the manufacturers of cutting inserts for CNC threading suggest tilting the insert at an angle $\lambda$ with respect to the $z$ axis (spindle axis on a lathe), so that the cutting edge/surface of the insert will work perpendicular to the groove it's "digging" (though that is true only at a very specific diameter [$x$ coordinate on a lathe], but let's not get into such tiny details).
See for example what the manufacturer Sandvik Coromant writes (link: https://www.sandvik.coromant.com/en.../how-to-choose-thread-turning-insert-and-shim):

My question #1 is: wouldn't such a tilting "widen" the profile of the resulting thread (i.e. increase the flank angle with respect to its nominal value) when the cross-section of the thread along the $z$ axis (not considering angle $\lambda$) is inspected?
I guess the "widening" of the flank angle due to the tilting is so small that it is still within the tolerances indicated by the standards?

And here's my question #2, closely related to the previous one: is the nominal cross-section profile of a thread (ISO, etc.) to be considered along the "threaded stem" axis (i.e. the lathe's $z$ axis) or perpendicular to the thread helix (thus taking into account the $\lambda$ angle)?
I've always thought the former was the correct cross-section to be considered.

Thanks for your attention.

 

[Lnewqban]

Regarding question 2, please, see:
https://en.wikipedia.org/wiki/Thread_angle

 

[Baluncore]

I guess the "widening" of the flank angle due to the tilting is so small that it is still within the tolerances indicated by the standards?

That is correct.
If the shank diameter is so small, that a tilt must be present, then the thread pitch is too coarse. The angle of the thread as a helix will then be too steep, and the nut will tend to come undone.

When cutting the thread, only the rounded tip and one side of the profile tool is cutting. The helical waste is then easier to curl, and can exit from the tool as a strip or helix without tangling. Between passes, the tool is advanced diagonally, parallel with one flank as the thread becomes deeper. By hand, that advance is usually done on the compound slide.

Normally, for reducing shank diameter, or cutting right-hand threads, you cut with the left flank of the tool, which for threads, has the lower relief angle, less chatter, and better finish. Meanwhile, you follow the flank on the right of the tool, where there is higher relief, but without cutting, so not damaging that less supported, so more vulnerable, right-hand edge of the tool.

Coarse pith threads on small diameter shanks, are the occasion that may require a tilt of the tool to increase the presented relief angle on the left-hand side of the insert.

 

[FranzS]

That is correct.
If the shank diameter is so small, that a tilt must be present, then the thread pitch is too coarse. The angle of the thread as a helix will then be too steep, and the nut will tend to come undone.

When cutting the thread, only the rounded tip and one side of the profile tool is cutting. The helical waste is then easier to curl, and can exit from the tool as a strip or helix without tangling. Between passes, the tool is advanced diagonally, parallel with one flank as the thread becomes deeper. By hand, that advance is usually done on the compound slide.

Normally, for reducing shank diameter, or cutting right-hand threads, you cut with the left flank of the tool, which for threads, has the lower relief angle, less chatter, and better finish. Meanwhile, you follow the flank on the right of the tool, where there is higher relief, but without cutting, so not damaging that less supported, so more vulnerable, right-hand edge of the tool.

Coarse pith threads on small diameter shanks, are the occasion that may require a tilt of the tool to increase the presented relief angle on the left-hand side of the insert.

Great, thanks a lot