Drawing critique / GD&T novice

[mrlizzard]

My GD&T is not to hot as learning! See drawing attached of a simple pre machined casting. Please add comment on my Datum choices and tolerance features - do they make sense? any comments are welcomed. Thanks

 

[KENAT]

Your drawing was barely legible, can I suggest you re-post perhaps PDF or I sometimes use monochrome tiff with high pixel count/resolution. Too large a file size and people will have trouble opening it but poor definition as at present and it's difficult to read.

Also, datum feature choices will depend on function, so if you can perhaps give some information on that, even mark up the print, it will help responses.

Finally if it's not on your drawing please state what standard you are working to, ASME Y14.5M-1994 or another?

KENAT,

Have you reminded yourself of faq731-376 recently, or taken a look at posting policies:

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

What is Engineering anyway: faq1088-1484

 

[mrlizzard]

New drawing attached (the drawing will be legible when zoomed at actual pixel level).

Standard is to ASM Y14.5M-1999.

The part is a cast inlet cone for a light vehicle exhaust system.

Important features are oval outlet, round inlet and 3x protrusions.

I'm not to sure how tightly toleranced the part should be yet.

Again I am new to GD&T and one of my questions would be is it ok to use the oval as a Datum?

Thanks

 

[PeterStock]

I see at least one dim to a hidden feature. This should be avoided if at all possible. Also I think that the current standards require all dimensions text to be horizontal, not angled as you are showing. (This might be overriden by a company standard.) A good practice with cast parts is to use datums that will still be there after machining, I think that your B and C datums look like they will be removed during machining.

Peter Stockhausen
Senior Design Analyst (Checker)
Infotech Aerospace Services

 

[PeterStock]

The Datum B in my post should be D. Also the standard I have seen is 3X instead of X3 for showing a dimension applies in more than one location. (Again company standard or practice may override.)

Peter Stockhausen
Senior Design Analyst (Checker)
Infotech Aerospace Services

 

[mrlizzard]

Thanks Peter.

Will look into the horizontal text and I think I will also denote datum B in a side view for clarity. Datum A,B & C are not removed by machining but datum D is. To get a datum plane similar to D is it legit to use the oval CL instead?

 

[KENAT]

Couldn't get the file to open, I'm guessing the server was busy however, regarding datum feature D.

You can't use the CL but I'm guessing you can use the width or length and get broadly equivalent.

Your datum features have to be actual features, where applicable a CL can be derived from these features. Take a look at Figure 4-13 in the standard and related text to try & understand what I mean.

KENAT,

Have you reminded yourself of faq731-376 recently, or taken a look at posting policies:

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

What is Engineering anyway: faq1088-1484

 

[mrlizzard]

I see. If I apply a Datum (D) to the width of the oval this will produce the datum plane as of the CL of oval? or should I use the one side of the parallel rib including 3 target datums?