UNJC rolled always
UNJC rolled always
(OP)
Can unjc threads be machined or do they always have to be rolled?
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RE: UNJC rolled always
RE: UNJC rolled always
http://www.iscar.com/eCatalog/Family.aspx?fnum=763...
RE: UNJC rolled always
UNJC [coarse threads, -1A or -2A quality, external] are relatively uncommon for Aerospace 'spec hardware'. In that case, good machining techniques and non-aero applications [or lightly loaded aero applications] may be fully acceptable. When application demands quality, such as -3A [highest quality, external], then I would expect nothing less than roll-forming.
However, high quality UNJF [fine threads, -2A, -3A quality, external] are virtually impossible to attain without being roll-formed. For this reason, and the obvious grain-flow benefits derived from cold-rlling, for fatigue life/strength improvements, etc, virtually all aero applications for UNJF threads are specified as critical and shall be roll-formed [whay pay so much for poorer performing cut threads?].
NOTE. All UNJF internal threads [-2B and -3B, internal] will be cut threads in forged parts such as for high quality/durability/re-usable high strength NUTS. UNJC-*B threads [internal] will be cut in all forms of material... forgings, castings, wrought-stock [MF from bar/wire, sheet or plate, etc) only when UNJC quality is required [otherwise UNC would be "good enough"].
Regards, Wil Taylor
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RE: UNJC rolled always
To elaborate a bit on wktaylor's excellent post, if you read MIL-S-8879 the stated purpose of the J threadform is for fatigue sensitive applications. So obviously the ideal method of producing an external thread would be roll forming. MIL-S-8879 also describes J threadforms based on 16-pitch, 12-pitch, 8-pitch, etc that go up to 6 inch diameter. At large diameters a rolled thread may not have the accuracy required to provide a fit with its mating part without excessive interference. Large diameter cl.3 threads often must be finish ground to obtain a suitable fit.
MIL-S-8879 also only describes 3A/3B class for any threads, including UNJC (table II).
Regards,
Terry
RE: UNJC rolled always
That'll teach me to re-review the specs [MIL-S-8879, AS8879] before engaging mouth.
Been too wrapped-up too tightly with UNF/UNC specs [H28] lately [on the old lady I work on]. Lots of detail parts [shafts, large pins, etc] use cut threads for the retaining nuts.
Regards, Wil Taylor
Trust Me! I'm an engineer!
Trust - But Verify!
We believe to be true what we prefer to be true.
For those who believe, no proof is required; for those who cannot believe, no proof is possible.
Unfortunately, in science what You 'believe' is irrelevant – "Orion"
RE: UNJC rolled always
However, there are a couple issues with roll tapping that must be carefully considered when used for producing J threads. One issue with roll-tapping is that the process tends to create burrs/flash of displaced flank material that protrude beyond the tip minor diameter, and these tip burrs/flash can interfere with the mating external thread's root fillets. The burrs/flash can also break loose when the mating part is threaded into the hole, producing metallic debris. Because of these issues, roll tapping is sometimes not permitted for aerospace applications.
Regards,
Terry
RE: UNJC rolled always
http://emuge.com/sites/default/files/zp10029_gb_cu...
RE: UNJC rolled always
High Quality internal threads are a bear... have created a lot of challanges for fastener vendors... look like asignificant advance
Regards, Wil Taylor
Trust Me! I'm an engineer!
Trust - But Verify!
We believe to be true what we prefer to be true.
For those who believe, no proof is required; for those who cannot believe, no proof is possible.
Unfortunately, in science what You 'believe' is irrelevant – "Orion"
RE: UNJC rolled always
Conformance of Roll Formed Internal Threads to AS8879
http://www.almanet.org/technical/docs/conformance_...
RE: UNJC rolled always
Link to very good article on AS8879 internal-threads, cut VS rolled.
Also, that website [www.almanet.org] has a LOT of very high quality industry-specific/related info.
Regards, Wil Taylor
Trust Me! I'm an engineer!
Trust - But Verify!
We believe to be true what we prefer to be true.
For those who believe, no proof is required; for those who cannot believe, no proof is possible.
Unfortunately, in science what You 'believe' is irrelevant – "Orion"
RE: UNJC rolled always
RE: UNJC rolled always
I had not heard of this type of thread gage before so I did a bit of research. The Johnson Gage Co. has a nice website discussing how these gages work. Thanks to your post I learned something new today!
Regards,
Terry
RE: UNJC rolled always
http://www.schraubenverband.de/fileadmin/redakteur...