implied positional tolerance? 1

[Tenkan]

Can anyone tell me if there is an ASME fundamental rule that applies to position of features shown on the same centerline with no positional tolerance?

I see many drawings where features are implied on the same centerline but a positional tolerance is not given (or no dimensions from each feature to the centerline). What controls their implied position to each other, and if this is not standard practice is dimensioning a feature to a centerline appropriate?

Some examples are a shaft with two diameters, or a part with a slot placed on center where the centerline is shared. I’m trying to argue the point but its been countered that’s the way its been for years so I wanted to find out if there was any implied centerline standard that I’m not aware of.


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[KENAT]

Koda94 ASME Y14.5M-1994 2.7.3 essentially says that no there is no assumed/implied locational tolerance or alignment or however you want to term it. You have to some how specify it be it by, geometric controls, general note requiring perfect form orientation/coaxiality... at MMC or otherwise.

This kind of question comes up regularly take a look at some of the previous threads - I think at some point I typed out a chuck of the standard

http://www.eng-tips.com/search.cfm?....7.3&t=&h=&searchSite=1&searchArea=1&d=1&s=1.

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[Tenkan]

thanks KENAT, the ASME standard you quoted answers my primary question exactly. I can now argue my point with reason.

my apologies for the redundant thread, I'll take some time to search topics in the future.

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[KENAT]

No problem, wasn't meant as an admonishment just that I didn't feel like giving a longer answer today!

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[Tenkan]

Honestly, I figured the answer easy. My problem is my company is asking we follow Y14 standards... but does not own them. (yes, I've requested them no no avail... yet) Since I dont own a personal copy I easily get stuck with simple questions like this, when it comes to changing creating drawing requirements its difficult to present my case on memory. I got frustrated with no one to turn to so I asked here...

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[flash3780]

You can pick up a used copy of the 1994 spec for $55 on Amazon... it's a worthwhile investment and it's still widely used.

http://www.amazon.com/Dimensioning-...ie=UTF8&qid=1367535664&sr=1-12&keywords=Y14.5

That said, it's a bit disconcerting that your company isn't willing to shell out a few bucks for a proper reference. In my opinion, the Y14.5 standard is required to produce clear blueprints... unless you're some sort of a savant and have the whole thing memorized... or just never make anything very complicated.

 

[pmarc]

You may probably want to buy the newest edition of Y14.5 standard issued in 2009. This is improved version of '94 edition.

 

[KENAT]

Pmarc, if his employer currently works to 1994 version and isn't planning on properly introducing the 2009 version with training etc. then one might suggest the OP get that version in preference to the newer one.

Just depends.

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[pmarc]

Of course, Y14.5M-1994 can be suggested.
I just have an impression (perhaps wrong) that the initial question wasn't limited to '94, but to ASME Y14s in general.

 

[KENAT]

The OP didn't say, I just meant to suggest he preferentially get which ever version he's required to use.

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[Tenkan]

pmarc is correct my OP was regarding Y14 in general, but KENATs suggestion is good though in regards to training that may be why the delay in purchasing the 09 standard... only seems to delay the inevitable though.

As far as the suggestions they are all great. I personally would rather keep up with the standards and get the 2009, but I didn’t think to look on amazon for a used copy. Although its more like $65 for the 94 standard used that’s within reach for a personal copy that would only help in any situation.

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[KENAT]

Koda, think about the users of your drawing - will they be up to speed on -2009 or are they still more familiar with 1994? I know it can be a bit of a chicken and an egg - if you don't require 2009 they may never learn it - but it's worth thinking about.

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[Tenkan]

I like your input KENAT but isn't the real question a matter of where the end user is going to get training on an old standard?

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[KENAT]

Koda, the last I heard the official ASME certification was still only available for -1994 version not the newer version.

My guess is most decent trainers can still offer either version.

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[pmarc]

There are some tools and chapters in ASME Y14.5-2009, not existing in '94, that can be really helpful even for basic level GD&T users, or I should say especially for basic level GD&T users.

But Kenat is right, most of training companies still offer classes per '94 standard. These courses will not dissapear just like that, I guess.