do you know a source, UNJF-3B 3

[dho]

I am looking for a tap, 1.000-12UNJF-3B, but with .005/.007 root radius.
you may say, for female thread, there is no root radius requirement from mil-s-8879, but as I know there is a trend towards that.
so, any place to get a special tap, if so called?
thanks.

 

[israelkk]

The requirement for root radius is relevant for external thread only.

 

[dho]

"The requirement for root radius is relevant for external thread only." is no longer correct.

 

[CoryPad]

dho,

Why did you state that "is no longer correct". Is that due to a specific customer requirement?

 

[WKTaylor]

Alll...

'In general' MIL-S-8879 was replaced by AS8879.

AS8879 P/N example and Figures 1 [ext thrd], 2 [int thrd] and 3 [int-ext thrds assembled together, tolerance study] clearly show controlled root radii for A [ext] and B [int] type threads.

REFs

SAE AIR5926 White Paper to Support Supersession of MIL-S-8879C With AS8879C
FAA AC21-41A Replacing MIL-S-8879C With SAE AS8879

Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true.
o For those who believe, no proof is required; for those who cannot believe, no proof is possible.
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion"]
o Learn the rules like a pro, so you can break them like an artist. [Picasso]

 

[dho]

"no longer correct", 1) the trend. 2) added (special) requirement.

 

[dho]

"AS8879 P/N example and Figures 1 [ext thrd], 2 [int thrd] and 3 [int-ext thrds assembled together, tolerance study] clearly show controlled root radii for A [ext] and B [int] type threads. " may not be persuasive as AS8879C no place in every and all the tables SPECIFY the root radius for female thread.
using standard thread tap, you will get flat root.
thanks to all.

 

[tbuelna]

You can certainly have a custom tap made that may give you a .005"-.007" root radius of the 1.000-12 UNJF-3B internal thread, but the thread may not meet the min major diameter requirement. So you might also need to modify the max major dia of the mating external thread to prevent interference between the external thread tip corners and the internal thread fillets. There is no problem with using modified UN thread forms as long as you clearly describe them on your drawing, and it is commonly done.

Also, rather than using a tap to produce this thread, I'd suggest milling the internal thread if possible. Milling the 1.000" cl.3 internal thread will give a better result than using a tap.

 

[dho]

yes, tapping may not be the best way to do the job. the thing is that our machinist already did the thread and missed the root radius requirement. so tapping is the only way to TRY. the major thread of a female thread per MIL-S-8879 is specified X.XXXX minimum. .005/.007 root radius almost like a sharp knife edge cutting deep into material, so there will be no issue mating a male thread.
thanks.