dimensioning to hidden line of internal thread major diameter
dimensioning to hidden line of internal thread major diameter
(OP)
Facing the circular profile of an internal thread on a detail drawing, to which line, (A) the solid line minor diameter or (B) the hidden line major diameter, should a thread callout/dimension arrow lie on?
Early in career, I dimensioned to the solid line by the basic idea of not dimensioning off hidden lines but I remember having been corrected about eight years ago with enough supporting material to place the leader arrow right on the hidden line (major diameter).
What is a good reference to support whichever convention?
Thanks!
Early in career, I dimensioned to the solid line by the basic idea of not dimensioning off hidden lines but I remember having been corrected about eight years ago with enough supporting material to place the leader arrow right on the hidden line (major diameter).
What is a good reference to support whichever convention?
Thanks!





RE: dimensioning to hidden line of internal thread major diameter
If you don't get the answer you want in this forum considering posting over in Drafting Standards, GD&T & Tolerance Analysis with a link to this one.
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?
RE: dimensioning to hidden line of internal thread major diameter
Regards,
Cockroach
RE: dimensioning to hidden line of internal thread major diameter
Link
Could not find international standards but the two links above provide a good start ESPECIALLY the second one (from "wisc.edu")which, on page 8, reflects a practical approach wherein an arrow points to, or lies on, the last operation performed. Reference to thread callouts in the first link ("morainevalley.edu") may be found on section IV.
With the above findings, I, personally, will now maintain pointing to the (hidden) major diameter just as when I was first corrected going back eight years.
Thanks to all who gave their input in this thread.
RE: dimensioning to hidden line of internal thread major diameter
RE: dimensioning to hidden line of internal thread major diameter
sounds to me like dimensioning the hole and show the tap ... by drawing note tagged to the hole axis ?
Quando Omni Flunkus Moritati
RE: dimensioning to hidden line of internal thread major diameter
Notwithstanding GD&T, I strongly suspect this varies by the type of industry, and many companies have their own drafting culture in which conventional protocol is thrown out to simplify or otherwise enhance detail that is more relevant to their internal workings. I have worked at companies in which the drawings, if submitted to a vendor for RFQ, would be the equivalent of sending them an ancient Greek manuscript, assuming that they are not fluent in that, as well, but were perfectly adequate for internal usage when taken in conjunction with work instruction, setup notes, machinists notes, etc.
It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.
RE: dimensioning to hidden line of internal thread major diameter
In Cat's 1E0500 spec for inch threads the one clear figure shows the callout arrow to the inside solid line.
Again, for what it's worth. Diego
RE: dimensioning to hidden line of internal thread major diameter
RE: dimensioning to hidden line of internal thread major diameter
Ted
RE: dimensioning to hidden line of internal thread major diameter
Just as in that one school's standards (earlier link) pointing to the "last operation," however opposite is your approach, it's a good/valid point. Again, not necessarily is there an incorrect way to do it.
Associating either the minor or major diameter with thread inspection, however, just may detract from the convention of the pitch diameter being of primary importance over the two other diameters. Inspecting to either minor & major diameters would not necessarily validate a thread's conformance to specifications; thread gages or the three-pin method oftentimes objectively validate threads/fits.
RE: dimensioning to hidden line of internal thread major diameter
Ted
RE: dimensioning to hidden line of internal thread major diameter
Attached is an example for both the external and internal threading specification required to a recent piece. Never had a complaint from the shop, I use the three wire method of pin measurement to use as a gauge on the box threads. This gets around the added cost in buying material for GO and NOGO gauges and then machining them to a four digit accuracy and sending them out to get hardened. If that's what you need to do because you work for some large corporation, that's fine, they have the deep pockets to cover that cost with added QC infrastructure.
It's not rocket science guys. Get a decent technical book from the store on machining and learn the trade. It really lends itself well to mechanical engineering, particularly when you can jump on the lathe and show the guys how to cut the thread yourself.
Regards,
Cockroach
RE: dimensioning to hidden line of internal thread major diameter
General consensus seems to be that tapping drill size information doesn't belong on the drawing per section 1.4e of ASME Y14.5M-1994.
Likewise from a standards compliance point of view the sample drawing you give doesn't control coaxiality of the various diameters as required by 14.5M. Chances are most of the time parts will get made fine anyway however if they're wrong there is case law that suggests the machine shop would not be held liable and you'd have to pay for non functional parts.
However, all this is getting a bit off topic from the OP. The question is arguably a slightly pedantic drawing standards issue that it's hard to imagine having significant real world impact. forum1103: Drafting Standards, GD&T & Tolerance Analysis is perhaps a better venue for that type of question.
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?
RE: dimensioning to hidden line of internal thread major diameter
Petrotrim Services
www.petrotrim.com
RE: dimensioning to hidden line of internal thread major diameter
Would caution, however, on Cockroach's approach. Hearing no complaints from a machinist would explain the adequateness of a spec and/or of the machinist's trade skills but there's always the underlying, and oftentimes overlooked, cost of inappropriately spec'd parts, not to mention the cost of rejecting non-conforming material.
RE: dimensioning to hidden line of internal thread major diameter
The shop makes the part to my specifications, that is what they get paid to do. I QC the part in order to prove the piece is to print. The MTR and QC print form part of the travel package traced to the piece.
You need to understand the process.
Regards,
Cockroach
RE: dimensioning to hidden line of internal thread major diameter
Machinists/fabricators interpret engineers' works and physically produce parts to/by industry standards. Uncoventional specifications will prompt questions here or allow for any misinterpretation; over-specification on the other hand may propmt unecessary procedures and raise costs. It is also here where drawings which have only been internal to a company would get tested whenever sent outside or when parts are outsourced.
Quality Control, not necessarily Engineering, measures/verifies the parts produced for conformity/compliance to the specifications set forth by design/engineering AND/OR by any Procurement or Quality Assurance PROVISIONS set forth in Purchase orders or Contracts--without any assumptions of its own as to part technicalities (form/fit/function).Problems arise, or operations are compromised, when this function is often mixed up with engineering and design. About the only time it is ideal the engineer/designer measures its work is at the development stage. Subsequent controls/measurements should serve as checks independent of design/engineering to reinforce objectivity in the process.
An effective Quality Assurance/Management System (QMS) would have provisions that allow for effectiveness and seamless transitions of the different stages, from the opening of a project or conceptualization, or from the receipt of an order or contract, to developing and producing parts, all the way out to delivery of finished goods.
Anyway, this is way off topic now. All it was was a matter of conventions and compliance.
Thanks, everyone.