New to GD&T - Could someone take a look at a drawing ive done? 3

[ELister]

I recently went through the ISO Geometrical Tolerancing course on the Engineers Edge site, I have basic understanding of most of the terms but applying it to a real life scenario is a different ball game.

I've attached a drawing I did of a Sheet metal door for a vehicle tool locker, when fully assembled this door has a recessed t-handle lock fastened to it.

Id really appreciate it if someone could have a look and simply give it as much constructive criticism as possible, So I can see if i'm on the right lines and have actually grasped the subject at all!

 

[CheckerHater]

Please re-post your drawing without using symbol "&" in the file name

"For every expert there is an equal and opposite expert"
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[ELister]

woops...

 

[KENAT]

What spec are you drawing to, certainly to ASME Y14.5M-1994 there are a few things that are off.

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[CheckerHater]

Well , OP says ISO.

KENAT, do you really think ISO and ASME are THAT different?



"For every expert there is an equal and opposite expert"
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[ELister]

ISO Kenat

 

[KENAT]

Checker, having worked an ISO system in a former life (though not necessarily that closely), and seen a lot of things claimed to be ISO that look off I wanted to check. Just cause OP went through ISO training does not always mean the resultant drawing is ISO - may just be that was the only training they found or something.

Thanks for clarification ELister.

A few thoughts...

Datums need to be associated to features not drawn center-lines (unless this is a nuance of ASME V ISO I'm forgetting). From your drawing it's not clear what Datum D or Datum A are meant to be the center line of or why they are different.

You don't appear to have a size tolerance on your rectangle cut out assuming the boxed dimensions are basic as is normal practice. The position tolerances should be attached to a feature of size (vague recollection of position being allowed to apply to a surface in ISO but I don't think that's relevant here) not to center line.

Do you really only care about 2 datums for your positions? In sheet metal there may be some justification for so doing, I'm just questioning if it was intentional.

I'd be tempted to dimension the rectangle with overall dimensions giving the size with tolerance +- in association with position on the size tols (or else surface profile applied to basic perimeter giving both size & location tolerance in one).

This is not everything.

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[3DDave]

ELister, what course did you take?

Maybe the course is one that experts sometimes give - it's correct, but skips a considerable amount the instructor is too familiar with and doesn't realize the new student won't understand what's missing from the course context.

OTOH
This

http://www.engineersedge.com/video/Preview-Fundamentals-of-GDampT_v1066

is painful to listen to and not entirely right (flatness would not be found if the surface was a smooth spherical surface as it hasn't got '3 highest points', even though there is nothing that prevents a surface having a low curvature meeting a flatness tolerance.)

Whichever - you have missed most of the point of D&T using feature control frames. Buy a copy of the ASME Y14.5 standard and look for 'differences between ISO and Y14.5' documents to fill in the rest. I don't know what to recommend for books. They can't be any better than the standard, but they may offer alternative explanations that better bridge what you already know to the standard.

 

[ctopher]

Datum D is called out 3 times, confusing.

Chris, CSWA
SolidWorks 14
SolidWorks Legion

 

[ELister]

Thanks all of you for your comments, its given me an answer to my reason for posting this which was 'So I can see if i'm on the right lines and have actually grasped the subject at all!'

Rather than spending hours going back and forth answering and asking questions about a drawing I already realise makes no sense to the real world, I've bought a book - ISO GPS Handbook by Henrik S. Nielsen, im going to go through this and start the drawing over and reapply the the GD&T to the drawing and see what the result is. As you lot seem so helpful ill post that drawing on the forum again sometime in the near future and see if I've got any further!

Cheers, Eddie

 

[tbuelna]

ELister-

Based on the drawing you provided, it does not seem that you have a full understanding of the subject of GD&T. First, it would help if your datums were based on a physical feature that can be measured, rather than the theoretical center lines of those features. It also does not make any sense to call out a positional tolerance for a feature to its self, which you did with the 3.0mm positional tolerance to datum A.

 

[ELister]

I have re-worked the drawing, and applied what I think I currently understand of Geo Tolerancing. If you guys could take a look again, scrutinize and criticize it as much as possible, and let me know i'd really appreciate it.

There's a few other changes to the drawing compared to the original as well as the changes to the GD&T, in case you are comparing the two.

Cheers, Eddie

 

[JNieman]

Up front... I'm familiar with ASME Y14.5 and not so much ISO... so apologies if I add any confusion, and please, I hope someone will correct me if I make a flub. But the "basics" of either group seem to overlap enough for the drawing shown.

The most important thing, the very foundation, of GD&T is to ensure your controls match the tool/part/product/assembly function. Second, is clarity of information.

Datum D confuses me. Is the datum intended to be the edge of the window or the centerline between the two right-most holes? You point to the window with a True-Position to [A] and then also with the same tolerance of True Position to [A|B]. Seems redundant.

Are Datums C & D intended to be the center of the sides of the cutout they are attached to, or the edges? ..Just to help verify that it says what you meant it to say. The True Position of the holes are located via Basic Dimensions to the theoretical centerlines of the window.

_________________________________________
NX8.0, Solidworks 2014, AutoCAD, Enovia V5

 

[ELister]

JNieman - Thanks for your response,

Datums C and D are intended to be the centre planes of the cutout feature, I think the Datum indicators should of been attached to the dimension line to show this, not to the extension line - I've quickly changed this and attached a small image to clarify what I've done.

In regards to True Position of the 3mm tols, originally I had just used [True Position|3|A] and [True Position|3|B] to locate the cutout, makes sense. However the ISO book I've been studying states that the sequence of the datum system should never change, meaning in this case, secondary Datum B should never be referenced to individually. So I used [True Position|3|A|B], to ensure that it is first aligned perpendicularly to Datum A, and then located 20mm from Datum B.

Yes, the true position of the holes are located via basic dimensions, to the theoretical centrelines of the cutout (Datums C and D). And the true position of the cutout is located via basic dimensions to Datums A and B. It does look confusing as the centrelines of the hole pattern are so close to the edges of the cutout, I added Detail B to show that there is a gap between them, perhaps there is a better way of showing this?

 

[CheckerHater]

First, I would designate big flat surface of the part as your primary datum.

Second, if your intention is for rectangular cut-out to be symmetrical about center, I would attach datum B symbol to the dimension line and drop 175.5 dimension.



"For every expert there is an equal and opposite expert"
Arthur C. Clarke Profiles of the future

 

[ELister]

CheckerHater - If the big flat surface was a datum, surely it would only control the perpendicularity of the cutout and the 4 holes. Would that be necessary for this part? Taking the thickness of the sheet and the position/size tolerances of the holes into consideration.

I have attached the datum b symbol to the dimension line and removed the dimension as you suggested.

 

[3DDave]

If the mating part has 3 of 6 degrees of freedom controlled by the big surface, then it should probably be the primary datum for features related to the mating part.

As a practical matter, will the part be set up on a CMM balanced on an edge? If not, then the part that lays flat on the CMM should be the primary datum.

 

[CheckerHater]

It would not "only" control perpendicularity, but rather it will control orientation of the entire datum system.

Given that your part looks like sheet metal it may have some interesting consequences:


"For every expert there is an equal and opposite expert"
Arthur C. Clarke Profiles of the future

 

[ELister]

Cheers guys, that image you attached made things much clearer CheckerHater