Inspection of "Stock" dimensions 3

[Mwoozley]

Hi. Can someone know of a specification that instructs inspectors how to properly interrupt a stock dimension? Currently, they are applying the drawings tolerance block leading to rejections and conflicts with our vendors. Thanks.

 

[MintJulep]

All "stock" materials produced to a standard already have a specification and associated tolerances.

What you need is a note on your drawings to the effect of "Dimensions and tolerances of standard stock per the controlling standard."

 

[KENAT]

Like Mint says, what ever standard defines the material should also either directly or [often] indirectly (that is it in turn references another spec) define the tolerances.

Posting guidelines faq731-376

http://eng-tips.com/market.cfm?

(probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484​

 

[Mwoozley]

Thanks. We have tried the note and the inspector's rebuttal was that "He doesn't have the tolerance from the 'controlling standard'". When you use this note, what directs your inspector's to handle the inspection of the stock dimension to the note's controlling standard?

 

[KENAT]

See

http://www.eng-tips.com/viewthread.cfm?qid=251334

the posts on 13th August.

ASME Y14.5M -1994 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)."

2.7.1.3 Form Control Does Not Apply (Exceptions to Rule # 1) The controls of geometric form prescribed by limits of size does not apply to the following:
(a) stock, such as bars, sheets, tubing, structural shapes, and other items produced to established industry or government standards that prescribe limits for straightness, flatness, and other geometric characteristics. Unless geometric tolerances are specified on the drawing of a part made from these items, standards for these items govern the surfaces that remain in the as-furnished condition on the finished part. ...

Posting guidelines faq731-376

http://eng-tips.com/market.cfm?

(probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484​

 

[MintJulep]

He doesn't have the tolerance from the 'controlling standard'

It is customarily the responsibility of the manufacturer to provide all of the documentation necessary to inspect a part. This would include the controlling standard in this case.

When you use this note, what directs your inspector's to handle the inspection of the stock dimension to the note's controlling standard?

Well, you could place a reference to the note adjacent to each dimension where it applies. Or you could further expand the wording of the note to make it apply to "stock material dimensions used 'as-received' without modification."

 

[Mwoozley]

Hi Kenat, This is a great and in the right direction. However, if you were an inspector doing a first article inspection, what tells you if the stock dimension is correct?

 

[Mwoozley]

Thanks for your help. I think you gave me enough information to work to build a corrective action.

 

[KENAT]

Mwoozley, fundamentally the inspector needs access to the relevant specifications. If internal then you can just get copies of the relevant standards (or online access or excerpts etc.) for him to reference.

You/He might even want to put a cheat sheet together for the common stock materials you see.

At the very least if he's not willing to take initiative then tell him that when there is a stock dimension he should ask for the relevant specification or similar - not use block tols.

Posting guidelines faq731-376

http://eng-tips.com/market.cfm?

(probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484​

 

[Mwoozley]

Hey. I looked up the quotes for ASME Y14.5.1M-1994 that were posted and it isn't there. Does anyone know what spec the quotes came from?

 

[Mwoozley]

Please ignore my prior post. My PDF's didn't have the qoutes listed, but my hardcopy of the spec has these quotes. Weird

 

[mfgenggear]

Mwoozley

It should be the Engineering Planner or Manufacturing engineer that should be specifying stock tolerances.
if it's sheet metal, machine shop or other. written instructions or a sketch specifying diameter, length or width.
stock material is spec by the raw stock suppliers. it's up to the manufacturing engineer to specify it's size.

the engineering drawing only specifies the material specification, if it's a forging, wrought or whatever.

some engineers do draw it if it's a casting,or a forging,

My 2 cents
Mfgenggear

 

[BillPSU]

mfenggear, I always end up having this conversation with the design engineer who says its not my job. The flatness tolerance on 1/2" plate is extremely large if you buy an A36 or A572 material. The tolerance specification was written many years ago and allows lots of variation in thickness and in flatness. Also today if you buy 1/2" plate you are actually buying a coil product which is decoiled and stretcher leveled.
The flatness of the part should be called out on the drawing and then it is up to the manufacturing engineer to produce a part to this tolerance. As a manufacturing engineer I need to know what you want and not rely on any stock note.

Decoiled material has a nasty habit of having coil memory and when a part is plasma cut or laser cut or oxy-fuel cut out of the end of the coil the part will end up looking like a banana because of coil memory.

Bill

 

[mfgenggear]

Bill

I am with you. I probably need to clarify!

I was specifying raw material stock & not finished product.
It up to the manufacturing engineer to specify what size raw stock material & what tolerance it will be.
as long as it is to the material specification of the drawing.IE AMS 6265, AMS 6415 etc.
He has to be cost effective, yet allow for any post process machining, fabrication or whatever.
The manufacture at his or her discretion can omit certain attributes & combined them at a later fabrication or assembly.
"nature of the animal". as long as the final product meets drawing requirements.

The engineering print drawing must call out all finished blueprint requirements.
the final part or assembly must be to the final drawing.

If the Design Engineer wants to specify the tolerance the print. he can as long as it part of the list bill of material.
which can aid fabrication. & He or she is correct.

HTH
Mfgenggear