Top Down Design - Making Drawings

[JWayman]

Good morning,
I have been asked to create a generic assembly. one which will enable the
prompt production of manufacturing drawings whenever a new variant of the
existing design is required.
The obvious approach is to create a skeleton to include the important
interface features, such as base surface, mounting features, etc. and to
publish geometry to the parts of the assembly in order to propagate the
changes arising from the new variant. All well and good so far.
However, as an example, if I insert the copy geom based on the published
geometry in the skeleton model to produce the base plate - select the copy
geom surface and thicken, then when I create a drawing of the base plate
there are no dimensions to show. All the dimensions live in the skeleton,
which is not in the model of the base plate. The publish geom/copy geom does
not result in any dimensions at all.
Similarly, let us assume the mounting features are two circular holes. I
create the appropriate circular sketches on the surface in the skeleton and
publish them. I then use the inserted copy geom from that published geom to
create the matching cuts in the part. I now have two holes in my part with
no dimensions and no axes. I go back to the skeleton to create the axes,
but, being a sketch on a surface I cannot use the axis point option in
sketcher.
What is the best way to use the skeleton part to enforce the design intent
down through the whole assembly to the parts, whilst still ensuring that I
can readily produce drawings to enable the parts to be manufactured? I
imagine I could create lots of dimensions, but I have already used the
dimensions I want to create the skeleton, so I want to use (show) them, not
create some more.
The use of 3D models to produce the parts directly is a step too far at this
stage, by the way.

I can think of sundry workarounds, like making the base surface an extrusion
in the skeleton and making the mounting features cuts, etc. but I want to do
this the 'correct' way.

All suggestions will be gratefully received and tried for size.


Regards,


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[dgschaefer]

First of all, I am a huge fan of top down design with skeletons.  I find it a huge benefit in maintaining design intent.

Secondly, I'm not sure there's a 'correct' way to implement a skeleton driven design.  The best way for you is going to depend on many things, the geometry of your design, the experience of yourself and your user base and even your level of comfort with various features in Pro|E.

That said, there is no way of bring the dimensions used to create your skeleton into your parts through the copy geom process.  But, many times you may not want to as those dims have relevance for the product or assy as a whole, but not necessarily for the individual parts.

For example, say a cell phone has a spec of being 0.75" thick and the rear case must be 0.50" thick to hold the components.  That makes the front case 0.25" thick, but there is no 0.25" dimension to show, even in the skeleton.  However, the 0.75" and 0.50" dims capture the design intent perfectly, creating the 0.25" dim would not.  by using a skeleton, you capture that intent directly and with two dimensions, letting Pro|E keep track of and do the math to find the third.  With out the skeleton, you do the math and must keep track of it if the specs change.

A skeleton gives you the freedom to think beyond the individual components and parts and think instead about the product or assy as a whole.  What makes it work, what dimensions need to be held.  Then you can think about positions, sizes and geometry differently, documenting that in the skeleton and 'hanging' the part geometry on the skeleton you've built after passing the relevant bits to the individual parts.

So, you'll need to use created dims in your drawings.  Personally, I've never been that bothered by creating drawing dims, but I see your point about having already created them and not doing it again.  I think you'll find that the control over your design you get by using a skeleton to think more broadly about your design as a whole is a much bigger benefit than the savings achieved by reusing model dimensions in your drawings.

Doug Schaefer

[swschultz]

I completely agree with Doug's insight regarding the use of skeletons. It's
a great tool, and hard to live without.



With that being said, there is a way to get skeleton dimensions to come
through into the models in which the skeleton geometry is passed, and that
is by merging the skeleton model into the components which require it. This
is not a solution for all top down design models and in fact it really only
makes sense to use in very specific cases.



There are a few main drawbacks to this approach. One concern is that the
entire skeleton is brought into the model through the merge process. You do
not have the same choice as you do with copy geoms where you can control
exactly which part of the skeleton to pass along to other models. With merge
it is all or nothing. In most cases you don't want to pass the entire
skeleton model into the components which require its geometry, you normally
only want to be passing very specific pieces of the skeleton.



Another main concern is that not only are the skeleton dimensions "showable"
in the drawings of the components in which the skeleton has been merged, but
they are also modifiable. This may or may not be a good thing. Changing
skeleton dimensions in the model in which it is merged will bi-directionally
filter those changes back to the main skeleton model. That's great, unless
you don't want other users to be able to make changes to the critical
constraints being controlled at the skeleton level. (Note that in the
component model you need to "Query Sel" passed the local geometry to reach
and show/modify the skeleton dimensions).



I have used this "merged skeleton" approach with great success in projects
such as certain types of casting designs, where the skeleton controls all of
the main surfaces for multiple cores as well as the main casting. This
allows me to show these main dimensions in drawings for each component,
while controlling them through a single model - the skeleton.



Best Regards,



Scott W. Schultz

Principal Consultant

3D Relief Inc.

3700 Willow Creek Drive

Raleigh, NC 27604

(919)259-0610

-



_____

[BrentDrysdale]

Hi John,
Yep, supporting Doug here too. We have been using Top Down Design with Skeletons for many years and I guess I did not think that created dimensions were any big deal. In a sense you can think of skeletons as the engineers job in setting the requirements/specification and the draftsperson's job to make a detailed drawing using that information. In our organisation it is the same deign people doing both aspects.

Sure making the drawing with created dimensions is some overhead if you look at it solely in those terms but the thinking and control are in the skeleton where they belong it is really a drafting presentation job rather than a design job. The trick is to have all the variants use the same drawing for each varying part and therefore the same dimensioning scheme but with changes to the skeleton simply updating the drawing(s) when you modify the skeleton and regenerate. Means you will need to look at your method of showing the variant name in the titleblock but the rest of the drawing will be done and the parts will always assemble correctly. You can add axes and the like to your skeleton and have these as the driver or make them through centres in your sketch. You can use the copy geom and then sketch your feature with use edge (loop is great) to make your extrusion you will get the hole axes but you still do not get dimensions unless you make reference dimensions in that sketch so why not just do them in the drawing?

Sounds like preaching to the converted anyway as you seem familiar with TDD and Skeletons; just questioning how to push the power on from that.

Sort of job that when well done looks really easy but typically there is quite a bit of work behind it.

Good luck.



Wayman John (external) wrote:Good morning,
I have been asked to create a generic assembly. one which will enable the
prompt production of manufacturing drawings whenever a new variant of the
existing design is required.
The obvious approach is to create a skeleton to include the important
interface features, such as base surface, mounting features, etc. and to
publish geometry to the parts of the assembly in order to propagate the
changes arising from the new variant. All well and good so far.
However, as an example, if I insert the copy geom based on the published
geometry in the skeleton model to produce the base plate - select the copy
geom surface and thicken, then when I create a drawing of the base plate
there are no dimensions to show. All the dimensions live in the skeleton,
which is not in the model of the base plate. The publish geom/copy geom does
not result in any dimensions at all.
Similarly, let us assume the mounting features are two circular holes. I
create the appropriate circular sketches on the surface in the skeleton and
publish them. I then use the inserted copy geom from that published geom to
create the matching cuts in the part. I now have two holes in my part with
no dimensions and no axes. I go back to the skeleton to create the axes,
but, being a sketch on a surface I cannot use the axis point option in
sketcher.
What is the best way to use the skeleton part to enforce the design intent
down through the whole assembly to the parts, whilst still ensuring that I
can readily produce drawings to enable the parts to be manufactured? I
imagine I could create lots of dimensions, but I have already used the
dimensions I want to create the skeleton, so I want to use (show) them, not
create some more.
The use of 3D models to produce the parts directly is a step too far at this
stage, by the way.

I can think of sundry workarounds, like making the base surface an extrusion
in the skeleton and making the mounting features cuts, etc. but I want to do
this the 'correct' way.

All suggestions will be gratefully received and tried for size.


Regards,

John Wayman
Mechanical Designer

Tel: 01963 372519


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[dougweaver]

John,

I agree with everything said above. A lot of times I find it necessary to create dimensions on the drawings anyways just because "design intent" dimensions often do not provide

good "manufacturing" dimensions. For example from a design intent standpoint it may make sense to create a hole pattern symmetrically about some virtual centerline.

From the manufacturing standpoint I would prefer to locate the hole from one edge of the part (since the shop can't measure to the virtual centerline).

I have also used the technique Brent mentioned, creating a ref dim in sketcher to be able to show that in the drawing (you can delete the "REF" text from the dimension and it

looks just like a "real" dimension). Admittedly it is another step but it does work quite well.

[ArnoldCollett]

You can also create a "driven dimension" note in the skeleton that can be added to a publish geom or selected in a copy geom feature. This can then be shown on the drawing or used in relations or patterns.

Arnold Collett