Use of "STK" for stock size callouts 1

[jlazzara]

Does anyone know if Y14.5 gives a definition for the "STK" notation?

 

[KENAT]

per Y14.38-1999, Abbreviations & Acronyms, STK is an abreviation for Stock.

However, it's also an abbreviation for Stack & Strake apparantly so make sure it's clear in your context, I'm guessing on a drawing this shouldn't be an issue.

I've used it on drawings.

 

[jlazzara]

Thanks for the assistance. That is part of the answer I'm seeking (I should have been a bit more specific).

Along with correctness of use, I'm trying to answer the question of how to properly interpret the callout. Unfortunately, I do not have access to Y14.5. The reference I have available is McGraw Hill's "Dimensioning and Tolerancing Handbook." This discusses usage of stock callouts as part of an exception to Y14.5's Rule #1. The handbook I am working with states, "Y14.5 exempts the following from Rule #1...Stock, such as bars, sheets, tubing, structural shapes, and other items prodeced to established industry or government standards that prescribe limets for straightness, flatness, and other geometric characteristics..."

To me, the above is a pretty good implied definition from the specification. I am wondering if the definition is spelt out explicitly as well.

 

[wes616]

The standard is unclear about this issue.

I think this may be part of the answer you are looking for:

If you call out STK meaning Stock size of a particular extrusion, you are not necessarily implying that you accepting all the manufacturing charactaristics regarding warpage, flatness, etc.

Your stock size is just a nominal dimenstion that you can do whatever you want with - but it implies certain material properties that you will use when you move into the analysis phase of your design.


Wes C.
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[aardvarkdw]

What are you trying to determine? Rule #1 just says that all dimensions need to be toleranced. Whether directly on the dimension, in a general tolerance block, or in a note, all dimensions must be toleranced. The exception you cite is for dimensional lumber, stock sized material, etc where the vendor supplies a tolerance to the material and you have no control over the finished size. Are you trying to determine if by putting STK after a dimension you are negating the tolerance? I would say, no.

You can specify the material size in a note and provide a vendor. I would then make any material size dimensions reference.

You need to provide either a tolerance on the print, a tolerance in an included document, or a vendor name and part number that you can use to determine what the tolerance should be.

David

 

[MadMango]

We spell out STOCK on our drawings, and usually only give 2-place tolerances (+/-.03"). This tells our shop they shouldn't machine raw material to the size. If we are concerned about profile tolerances, straightness or other factors, we'll add a ASTM specification to the General Notes.

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

Have you read faq731-376 to make the best use of Eng-Tips Forums?

 

[ewh]

We apply any STK dimensions as reference, i.e. "(.XXX) STK", unless further control is required

 

[CheckerRon]

ASME Y14.5M ¶ 1.4(a)states that "Each dimension shall have a tolerance, except for those dimensions specifically identified as reference, maximum, minimum, or stock (commercial stock size)." I therefore add "STOCK" or "STK" to such as unmachined plate, sheet, or formed thicknesses, to override the block drawing tolerance. This, as wes616 said, doesn't cover form variations, so if those are important to you, you need to specify them separately.

 

[ewh]

Thanks, CheckerRon. I guess I've been using suspenders with my belt!

 

[thundair]

This is one of my pet peeves. IMO... stock size is one that is not altered from the manufacturer I.E. the profile of an angle or tube or plate....All cut sizes need to allow/show tolerance even if it is .250"

Cheers

I don't know anything but the people that do.

 

[aardvarkdw]

Exactly, a stock size is a value that is supplied by a vendor and that you as a designer have no intention of altering. Any alterations to that number make it no longer stock and therefore need a tolerance.

David

 

[Tunalover]

The raw matl manufacturers go by industry standards e.g. ASTM, AA, SAE, ASM, UNS, etc.. If you have the spec(s) you use to call out the material in your note then there's a trail you can follow where it will (eventually) show acceptable size limits. This is expensive and time-consuming (Machinery's Handbook has many). Generally these industry standards (there are several for, say, AL6061-T6) produce the same mill tolerances for the same item. In order to control mill tolerances you must call out the governing standard(s); it's sloppy to simply call out, say, AL6061-T6 with no governing spec (although supplier due diligence will typically get you what you need). For sheet metals the mill tolerance is a function of nominal thickness and sheet size. Rule #1 of ASME Y14.5M-1994 is exempt on stock dimensions because of bowing and other such irregularities. If you can't live with bowing (can' exempt Rule No. 1) and your part has a stock dimension then you need to use a "hard" dimension (not a STOCK dimension and not a REFERENCE dimension) on that feature to prevent bowing. In this case you would need to make sure that the mill tolerance doesn't exceed the tolerance you apply to the hard dimension (otherwise the fabricator will have to machine, sand, or grind the matl).







Tunalover