internal and external thread undercut

[SAEEDGH]

hi
does anyone know iso standard number for internal and external thread undercut (thread relief)?
i know iso 4755 for external thread.

 

[Burunduk]

It's not ISO and it's not specifically for threads, but there is DIN 509, which is generally for external and internal undercuts on turned parts.

 

[Wuzhee]

Here you go. I use these for threads too, you can always take inspiration.

 

[3DDave]

It does not appear that DIN 509 provides sufficient relief for thread runout which ISO 4755 does do.

 

[CheckerHater]

Not sure about universally accepted standards, probably more like company standards.

Try this for example:

https://files.engineering.com/getfi...8dfa-61e5a0f3704e&file=thd_relief_chart_2.pdf

"For every expert there is an equal and opposite expert"
Arthur C. Clarke Profiles of the future

 

[3DDave]

On external threads there is often concern about surface finish and diameter of turned-down area and fillet radii to ensure that no stress risers are created. On internal threads those won't matter.

If understanding the stress and fatigue results of this is important I would not depend on a standard that doesn't mention the effects on those areas.

Oh, the typical geometry allowances are to provide mechanical clearances for typical taps and dies, so they include the distance from a wall that the threads must terminate on an external thread and the distance from the bottom full minor diameter drilled hole for an internal thread.

 

[Prometheus21]

Like 3DDave states the typical geometry allowances are to provide mechanical clearances for typical taps and dies. Often it is defaulted to 1.5-2 x P or 2-3 x P. Now there are of course taps that have shorter runouts, like 0.5-1.0 x P, typically called (chamfer) form E or form F for an even shorter runout, but it varies.

Like CheckerHater says it is often a company standard; with variations based on the DIN 509 or ISO 4755 (at least by a number of European manufacturers)

 

[Wuzhee]

It does not appear that DIN 509 provides sufficient relief for thread runout

Yes, you're right. 509 isn't for threads, but I said, you can take inspiration from it.

When I have to design undercuts I mostly take hint from DIN 509 Type E undercuts and I change my geometry according to the requirement.