Help with Threads

[Reverend Turk]

This has nothing to do with MC other than I am programming the part with MC but I just got a request to make all holes UNJF-3B. I have never had to do a J series before and I am not sure what I will need to do different to make the thread a J with a fit of 3. The tap is 8-32. Do I have to get a special tap? Hope someone can help!!!

[Guest]

i would look in the machinery handbook. there will be more info than you would ever need to know about thread fits and classes of fits.hth

[Rick Henrickson The Boeing Co.]

Id thread not special

[Rick Henrickson The Boeing Co.]

I dont think J threads are in the handbook!

[mcpgmr]

Nothing special to do. Just have to have the right tap that's all.

[Span]

Standard tap, larger minor diameter. If I can find the spec. I'll post it.

[Span]

Minor dia. is .1336/.1417 using Thread disk.

also found it here..

 

page 27

[Carl Vallance]

From ThreadTech v2.21

 

..............OSBORN PRODUCTS INC..............

Pitch diameter tolerances and other data for INTERNAL

THREADS, class 1B, 2B, 3B, series UNC, UNF, UNEF,

UN, UNJ, UNS.

 

Number of starts............................... 1

Threads per inch............................... 32.0000

Decimal lead is................................ 0.03125

 

.164-32 UNJC-3B INTERNAL THREAD

 

The pitch diameter is......................from 0.1437

to 0.1465

 

The minor diameter is......................from 0.1336

to 0.1417

 

Pitch diameter tolerance for 3B is............. 0.0028

The helix angle is............................. 3.95980

Or if you prefer 3 Degrees 57 Minutes 35 Seconds

These are COMPUTER values......................

Run date is 07-24-06

[pip]

I think its an aerospace call out. As span says, just a larger minor diameter. Span, thanks for the link have copied it.

[Rotary Ninja]

That is a military specification thread.

Formerly Mil spec number MIL-S-8879

 

Now known as SAE AS 8879.

[tryon]

UNJ have a controlled root radius.

[Reverend Turk]

Thanks for all the great info

[Reverend Turk]

Ok..I thought that would solve my problem but I am being told that I need to do more than just use a 3.5mm (.1378) drill before tapping with a regular 8-32 tap! Does anyone know where I can get an 8-32 UNJC-3B tap????????????? I need this fast!!!!!! Thanks in advance

[Rick Henrickson The Boeing Co.]

the controled root radius is only affected on od threads I have the specs

 

minor .1336 / .1417

pitch .1437 / .1465

minor .164 min

 

no mention of root rad for internal

per mil-s-8879c

[Reverend Turk]

So I should tap with a regular tap right??? I keep researching this and coming up with different answers. Getting cob=nfused with a BIG headache!!

[Rick Henrickson The Boeing Co.]

http://www.uscti.com/TapsFinal2.pdf

 

just use standard 3b tap increase minor and check above link.

 

that spec I listed is right out of the book

rads only affect od threads in J form