Repetitive Features

[i2xtreme]

I have seen one customers drawings come through with a call out like the following and it drives me nuts:

.138-32 UNC-2B
3X

To me it seems in order to comply with ANSI/ASME Y14.5M-1994 you should call out the above like this:

3X 6-32 UNC-2B

In section 1.9.5 (repetitive features or dimensions) it does not state where the "3X" has to be... but in sections 1.9.5.1 (series and patterns) and 1.9.5.2 (spacing) it states "...number of features and an X followed by the size dimension of the feature.)

So does this mean the first call out is okay?

Is calling the threads out by .138 even legal? I would think using the screw designator is the proper way (6-32) Who orders a .138-32 tap?

Thoughts? Does it really matter?

 

[weavedreamer]

The location of the 3X is crude, but it is still descriptive.

If you bid the price up on the 'special order' tap, you may inspire a change, or someone more 'forgiving' might just bid using a 6-32 UNC-2B.

 

[MadMango]

Decimal conversion of tap sizes seems to be a standard practice for military and aerospace. At least they didn't put the diameter symbol on it too.

"Art without engineering is dreaming; Engineering without art is calculating."

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[ctopher]

I always put the qty first. The Machinist Handbook can tell you what thread size to call out.
I have seen drawings with all threads called out with the decimal shown. This is confusing. Calling out ".138-32 UNC-2B" vs "6-32 UNC-2B" can mistakenly give you a different tolerance.

Chris
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[i2xtreme]

So whats correct according to Y14.5?

 

[weavedreamer]

ASME Y14.5M-1994 1.9.5.1 Series and Patterns. Features, such as holes and slots, that are repeated in a series or pattern, may be specified by giving the required number of features and an X followed by the size dimension of the feature. A space is used between the X and the dimension. See Figs. l-52 through l-56.

Is it grounds for rejecting the drawing? You were able to determine by looking at it how many there were altogether, yes?
As to the thread designation - it is not in ASME Y14.5M-1994's scope. The drawing states .138-32 UNC-2B and the Machinist Handbook gives the nominal dia of a 6 as .138

 

[aardvarkdw]

"...an X FOLLOWED by the size dimension of the feature"

I think this is pretty self explanatory. The dimension comes after the qty. Although it could be argued that because they use the word MAY, this is not so much a requirement as a suggestion. I don't think there is anything wrong with the thread callout, it may not be what I would prefer to see but the notes' form is otherwise correct.

David

 

[ewh]

I realize that "6-32 UNC-2B" may be the proper callout per some standard, but any decent machinist or designer will not confuse ".138-32 UNC-2B" with an off-the-wall tap size. I would not reject (and have never had one rejected) a drawing for this reason.

 

[Heckler]

IAW ASME B1.1 section 6.1 screw thread designation both calling out fractional and decimal thread designation is acceptable. If you want even more control the Major Diameter and Pitch Diameter can be used.




Heckler
Sr. Mechanical Engineer
SWx 2007 SP 4.0 & Pro/E 2001
o
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This post contains no political overtones or undertones for that matter and in no way represents the poster's political agenda.

 

[KENAT]

I'd say the 3X should be first. I think when the standard says the X 'may' be used it's talking about using X instead of dimensioning each one or saying 3 places. As such my understanding is that if using the X it should be in front of the dimension.

UN threads in the US are covered by ASME B1.1-2003. According to section 6 the way the thread is called out is perfectly legal to this standard.

6.1...The nominal size is the basic major diameter and is specified as the fractional diameter, screw number or their decimal equivalent. Where decimal equivalents are used for size callout, they shall be shown in four place decimals (omitting the cipher in the fourth place) for fractional sizes, and in three places for number sizes...

Now the problem may be that most drawings in the US don’t actually reference B1.1 so almost no one actually knows what spec is controlling the threads and seem to rely on Machineries or similar;-). Seriously thought ASME Y14.6 which is referenced by 14.5 says:

3.2 Thread Specification
In the U.S. the name and number of the controlling thread standard is frequently omitted from the drawing. Reference is made instead to the designation symbols of the standard, such as series symbols and class symbols. To avoid misunderstanding, it is recommended that the controlling organization and thread standard be specified or otherwise reference on the drawing.

I just turned the page and 14.6 section 3.2.1.3 actually suggests that just the number size shouldn’t be shown, but if used should be followed by the decimal in parenthesis (we do this). This is a slight mis-match to B1.1 which seems to say you can just have the number. The copy of 14.6 I have is 2001 although 14.5M-1994 references the 1978 edition.

Either way though, the thread designation you have would appear to be legal assuming the drawing somehow references, directly or indirectly (e.g. by calling up 14.5 in the title block etc.), 14.6 or B1.1.

Now if these standards aren’t referenced in any way then arguably you can do what the heck you like, which is why I’m a stickler for somehow referencing any invoked standards.



KENAT, probably the least qualified checker you'll ever meet...

 

[KENAT]

Darn Heckler, you posted while I was typing my diatribe and beat me to the punch.

KENAT, probably the least qualified checker you'll ever meet...

 

[btrueblood]

KENAT,

Once again somebody has absconded with my Y14.5 copy. Does Y14.5 not still reference ASME B1.1 in its list of referenced documents?

If so, and if you explicitly reference Y14.5 on a drawing note, and then add a second note referencing ASME B1.1, should you put that 2nd note in parentheses (indicating it is a reference for reference only), since it's already referenced in the Y14.5 standard?

Seriously, as KENAT points out, if there is a discrepancy between nomenclature/callout form between the two standards, which one takes precedence? If you really are going to go down this specification and standardization route, and have multiple referenced standards/specs on your drawings, you need to include a note regarding OOP. Been there, seen a company tied up in knots by a nasty government-paid QC type, bought a ticket out.

 

[KENAT]

btrue: 14.5 only references 14.6 not B1.1. 14.6 does have B1.1 in it's 'applicable documents' list though. 14.6 only covers thread representation, it doesn't define the threads, this is B1.1.

14.6 isn't particulary well worded on the issue:

3.2.1.3 The nominal thread size is the basic major diameter and is specified as the fractional diameter, screw number or its decimal equivalent. Where decimal equivalents are used for size callout, they shall be shown in four-place decimals (omitting zero in the fourth place) for fractional sizes and in three-place decimals for number sizes.

… Examples…

Numbered sizes may be shown because of established practices. The decimal equivalent, to three decimal places, should be shown in parentheses. Examples are as follows:

No. 10 (.190)-32 UNF-2A
or
10 (.190)-32 UNF-2A
or
.190-32 unf-2A

The first paragraph implies you can have just the screw number while the second says you shouldn't, maybe it's just clarifying what the first paragraph said but I'm starting to lose track of my thoughts.

However for the OP, regardless of which standard, the designation was correct.

btrue, in your case I belive the problem was the QC guy more than the standards.

KENAT, probably the least qualified checker you'll ever meet...

 

[Heckler]

No, ASME Y14.5 does not call out B1.1 in its reference section 1.2. It calls out ASME B1.2 in section 1.2.1 additional sources.

In my experience with working defense/military contracts if it's spelled out in the requirements document or unless you have taken exception to it in the complience matrix then you're on the hook.

Heckler
Sr. Mechanical Engineer
SWx 2007 SP 4.0 & Pro/E 2001
o
_`\(,_
(_)/ (_)

This post contains no political overtones or undertones for that matter and in no way represents the poster's political agenda.