Thread callouts

I currently can not get my employer to purchase ASME Y14.6, and we have
some serious disagreement in our group about how threads need to be
called out. I am putting together our "standards" and need to have
reasoning/proof behind what I put in it, in order to show it isn't just
"my opinion."
Can anyone tell me what this document actually says is correct? Or if
you just want to tell me how you do it, that is fine, but give some
reasoning behind it please.
Here are the different variations I am seeing for a 1/4", 20 thd/in
tap.

1/4-20
1/4"-20
1/4-20 UNC
1/4"-20 UNC
1/4-20 UNC-2B
1/4"-20 UNC-2B

Thanks guys/gals.
Steven

 

Here is what the standard says.

..250 - 20UNC - 2B

First nominal diameter in decimal, then dash, then threads per
inch/lead, then thread form and series, then dash, next class fit
designation, then finally any qualifying information ex. MOL, SPL, LH.

This was pulled directly from the ASME code book.

 

My vote would be for #5-- if you want to specify a source other than Y14.6
to justify yourself, you could use Machinery's Handbook as an authority.

That said, I suspect that any of the 6 callouts would work just fine--is
this really a battle that you need to fight?

 

Its just a symptom......

First its thread call-outs......
Then revision schema.....
Followed by Title Blocks......
Summed up nicely by file naming conventions and classifications......

Using a known standard removes the "ego" from the equation. And for
whatever reason there appears to be a fair amount of it in any company.

Eliminates the "this is the way its always been done around here" or
the "I remember when...."

Don't know how many times I've heard managers ask if the PDM I use can
control file names and locations (i.e. prevent somone from doing an end
run and putting files on their local drive -- for archiving purposes of
course!"

Been caught in his dilema more times than I want to remember.

Good luck.

Len

 

Steven,

I agree with SWX-VAR-JP, except I think the spaces are not needed. I
don't have the official ASME Y14.5M-1994 standard, but I have a good
reference book (which I recommend) called "Design Dimensioning and
Tolerancing", by Bruce A. Wilson, which is based on the latest ASME
standard. It says the minimum amount of information that must be given
for a thread is the "nominal size, threads per inch, thread form, and
thread class". It shows an example as ".750-10UNC-2B" for threads that
go through a part, or if thread depth needs to be called out, such as
for a blind tap, then the example is ".625-11UNC-3B (insert depth
symbol).62", where the depth symbol is a "T" with an arrowhead pointing
downward. Also, the book notes that nominal size for Unified National
Course threads is equal to the maximum size limit of the major diameter
on an external thread. Lastly, it notes that additional information
can be found in ANSI Y14.6.

Hope this helps settle your differences, although I would stress that
in my experience, most shops have a practicing set of standards that
are "what the guys on the floor are used to", and the official
standards don't always have to be followed to the "T", especially if
drawings are for "in-house" purposes. I would choose my battles in
deciding what is best for your place of work, and in some cases just go
with the established precedent.

Cheers,

-JOSH