Should one be able to do a tolerance stackup from a GOOD assembly drawing 2

[supergee]

I am a still new college teacher.

Last semester, I tried to convey what is a proper assembly drawing to my GD&T class student, effectively trying to make them forget the nice looking yet not always practical exploded view they saw in the much more interesting previous CAD classes.

yet, I have all sorts of results that do not depict all part or showing the parts with a scale such as the parts depicted are to small to be seen by human naked eye.

Next semester, I would like to tell my students that if they are not able to do a stackup analysis from they're assembly drawing the views aren't right.

What are your opinion on this? I know ASME Y14.23 states that "depiction of the items in the assembly relationship,using sufficient detail for identification and orientation of the items." but I feel this is very clear for someone who already knows what a good assembly drawing looks like...

 

[geesaman.d]

The only thing required from an assembly drawing is multiple components in their assembled state. The identification, quantity, and orientation of each component does need to be made clear somehow - ambiguity is never acceptable. Even "obvious" things like jam nuts under regular nuts, or flat washers under lock washers, or ... are not done the same way in all situations and must be clearly documented.

I think students need identify who the audience of the assembly drawing is and then provide a sensible set of supporting data for that audience. The more students learn that a drawing is a communication document to a reader, the better impact their designs will have.
Possible audiences:
1) An assembly drawing for an assembler who will put the parts together
2) An Inspection drawing for a final inspector who will assess the conformance of the assembly
3) An internal assembly drawing for Engineering to store critical design data and jump off into detailed component information
4) A General Arrangement for a customer who is using this information to integrate the equipment into a larger system installation
5) An assembly constructed for related design team, such as automation and controls or electrical power, looking for tie-in and measurement locations.
6) A parts sectional drawing for a customer ordering spare parts

I might argue that context 1 and 3 are mandatory skills and the rest may not be required. At large companies, the other stuff may be subbed out other designers but 1 and 3 pretty much need to come from the engineer who designed it. If you don't communicate your designs clearly you've not earned your paycheck as an engineer. (Please quote me on that!) I've seen some wildly smart engineers do great design work fall completely flat because they didn't communicate the design clearly.

Full scale drawings continue to fall out of use, so laser-printed 11x17 is now the most common way to printing drawings in my world. The font might get squinty small but ideally the drawing will be readable at this printed size. Detail views, break lines, and special section views are common practice.

The more detailed data - detailed bill of materials (columns beyond quantity/item number/part number), dimensions, bolt torques, weights, loads, part numbers, center of gravity, assembly notes, assembly instructions, bearing endplays, exploded views, consumables and sealants, etc, etc, are entirely up to the context.

I rarely use exploded views. They can be very helpful graphically but as a regular practice they're time consuming to construct and maintain compared to sectional views that don't need to be adjusted constantly as the design evolves. Parametric software handles design changes very well but the exploded views are always blowing up and spilling off the page. They're also bewildering for more complicated assemblies.

For fun, consider watching the movie "Hudsucker Proxy" as a perfect example of a drawing that did not deliver message. (I suppose you'll have to watch it all, but the drawing bit can be compiled into a couple minutes).

Not sure about the stackup analysis comment, since you'll still need to read each component drawing to get the limits of size for each part feature. But I do agree that the assembly drawing needs to show the relationship of the parts to each other to perform that analysis.

 

[CheckerHater]

supergee,

The kind of drawing you are talking about is called LAYOUT DRAWING.

According to ASME Y14.24
"A layout drawing ... is prepaired either as:
...
(d) A geometric study to develop movement of mechanical linkages, clearances, or arrangements."

And this is where your study of clearances and fits happens.

Layout drawing may serve for further creation of assembly and detail drawings, as preliminary assembly drawing, or, when developed enough, as assembly drawing itself.

Today many functions of layout drawing are passed to CAD model, so it becomes less-known relic of paper and pencil past.

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

 

[ctopher]

"stackup analysis" and "layout assy dwg", two different things.

Chris, CSWP
SolidWorks
ctophers home

 

[drawoh]

supergee,

The basic functionality of an assembly drawing is that it should describe to the device is to be assembled. For an assembly, I want to see orthogonal views with sections and details and whatever else is needed to show functionality. This can go on the assembly, or on an arrangement or on a layout.

--
JHG

 

[dgallup]

You could never do a stackup analysis from an assembly drawing. The assembly stackup will depend on the component dimension and tolerance scheme which are only on the component drawings.

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[drawoh]

dgallup,

You pull the dimensions and tolerances from the fabrication drawings.

You copy them to the orthogonal assembly view and work out the absolute positions.

--
JHG

 

[supergee]

Thank you all for your responses, they will weight in my reflexion (Ok ... I don't know if this is proper English... makes sense in French)

Maybe the stackup analysis is too far fetch. I will try to convey what I want more explicitly and use some of this semesters drawing as what NOT to do.

Gee

 

[dgallup]

Drawoh,
Now you have dimensions and tolerances on two drawings which is expressly forbidden.

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The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.

 

[Garland23]

Dgallup, in paragraph 4.1(l) of the 2018 standard, it says that dims and tols "apply only at the drawing level where they are specified." It doesn't use any language such as "shall" or "shall not" regarding having the same dims/tols repeated at another level.

 

[drawoh]

dgallup,

Your assembly or arrangement drawing can have reference dimensions and tolerances, copied from the fabrication drawings of course. Tolerance stackups are not meaningful on fabrication drawings. As a rule, tolerance stackups are not a final deliverable. They are an analysis. You do the analysis. You think about the analysis, and then you make decisions.

My final tolerance stack up file is a spreadsheet.

--
JHG