Special DIN 405 thread callout?

[NinerEng]

Hello,

I am working on specifying an external thread that I have measured on a part.
From what me and our experienced machinist have been able to conclude, it is a non-standard DIN 405 thread with a full root radius and truncated outside diameter.
That being said, I am having trouble finding the appropriate method to call this thread out on our print.

Measurements
Measured thread OD: 18.542mm
Measured thread pitch: 2.54mm
Measured thread ID at bottom of root: 16.002
Measured length of thread: 5.97mm

Proposed call-out:
RD 18.452 x 1/10" ↓ 5.97 DIN 405 SPL
PD 17.27

Note: This drawing is in inch sheet format for all other dimensions

Any feedback on this would be a huge help. Thanks

 

[Tmoose]

Can you confirm if the actual threads are 55° or 60° threads ?

Some of those dimensions sound a little Whitworth-y.

https://www.trfastenings.com/knowledge-base/thread-geometries/british-standard-whitworth

 

[juergenwt]

Looks like a somewhat mutilated 3/4-10

 

[NinerEng]

Tmoose, they're actually 30deg per the DIN standard. Also the thread root has a much larger radius than most standard threads.

If it wasn't truncated the thread shape would essentially be a wave because the radius of the crest = the radius of the root.

I'm pretty confident in the identification of the thread but the proper way to call it out is where I am struggling because it's essentially some oddball German standard

 

[3DDave]

That callout probably won't define the tolerance on the values.

I'd would ignore the thread spec and just define it on the drawing completely using the thread specification as a guide. The special threads I've seen have used a standardized thread form and pitch and just changed one factor - this looks like hardly anything is unchanged except the angle. For certain there isn't a thread gauge that's any better.

DIN 405 threads aren't truncated, so you need to specify that separately, hence just make a drawing standalone and skip the DIN 405 reference.

The included angle is 60 degrees, it's just DIN 405 uses the flank angle which is half of that. Pesky Germans.

https://www.ring-plug-thread-gages.com/ti-spec-DIN-405.htm

Edit: different sources say either "1/10" or that the pitch is threads per inch. Anyway - skip that trouble and fully define.

 

[NinerEng]

3DDave,
Thanks for the info. When you mention just calling it out without using the DIN 405 reference, how would that look from a syntax standpoint using the values that I have above?
I don't have access to the standard which calls out the formatting for these threads.

 

[3DDave]

You still need to establish tolerances, which you won't get from the standard. The standard also doesn't handle truncation - which you say you have. You would not "call it out" at all, no syntax, no formatting - you would draw it just like the many other thread standards do with a profile view and dimensions - plenty of examples on websites.

 

[NinerEng]

I called it out as best as I could in the image here.. The flagged number 3 references a note that says to check the thread with a mating part so they don't need to measure the PD. Not sure if this is the best way but it's the best I could come up with.

 

[Tmoose]

Is the threaded part "used in coupling gears and brake rods in railway waggons, valves, slides, fittings and by the fire brigade." ?

 

[NinerEng]

Tmoose, it is a fitting application on a medical device. Used to quickly seal a connector with an O-ring into a cap without too much rotational movement needed.