Constraints/Dimensions or No Constraints/Dimensions in 3D Modeling

[Jasonb]

It would be better if Jason called the database number a "value", and a dimension is what is displayed on the screen to reflect that database value.

That is what it really is in my opinion.

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Now why would I want to do that, Gordon started the thread that initiated this one and he has chosen to use Alibre Atom3D. Alibre refer to the "values" entered into boxes as you sketch parts as DIMENSIONS.

Take a look at this very first part being described in the Atom3D beginners playlist, should start just before he mentions dimensions



It's not just Aliber who use the same terminologyn. As I have said I also use F360, mostly for CAM but do sketch a bit with it. Again first in lars' F360 for beginners series and he too refers to entering values in boxes as dimensions



I'll leave it to you as to what you want to call things but best mention you are talking specifically about Solidworks wording to stop people getting confused

 

[GreenTwin]

I have never used SolidWorks, but based on Pat's descriptions of his process, I wonder if "setting the size" of a part works somewhat differently than it does in some other 3d CAD programs. In FreeCAD, when I draw a rectangle and want to set its size, I click on a side and click on the "vertical height" constraint and enter a number - and it shows up in the sketch just like a "dimension" would show up on a 2d drawing. But it sounds like in SW, perhaps one pulls up a dialog box and sets various size parameters there, which do not necessarily show up on the sketch. The size is there, constraining the sketch, but no "dimension" shows up unless a setting is enabled.

The more I think about it, the more I wonder if it would be helpful for the CAD world to adopt something like "size" and "position" when talking about constraining the shape and position of an object, and save "dimension" for the "printed" numbers that are intended only to communicate that size / position.

Solidworks does have a dialog box on the left side, and when you are creating a shape or line, the parameters (values) for that object appear in that dialog box, and any of them can be edited while that object is highlighted, or at a later date.

But the values in the dialog box are not relations in Solidworks.
Those relations have to be called up in a separate "relations" dialog box, and manipulated separately.

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[GreenTwin]

I'll leave it to you as to what you want to call things but best mention you are talking specifically about Solidworks wording to stop people getting confused

I think it is a Tower of Babel thing to some extent, but people ask for free help here, and I try to give it.
I think we need to really use global terms, since most of use don't have multiple 3D programs, and we don't necessarily know the differences between all of the 3D programs.

Best I can do really is share concepts.
Others will have to translate that to their 3D program; I can't do that.

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[GreenTwin]

I'll leave it to you as to what you want to call things but best mention you are talking specifically about Solidworks wording to stop people getting confused

I normally do that, and would advise others to do the same.

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[petertha]

I'll try to expand on terminology used in SW.

Typically a dimension is entered by 1) clicking on the required entities and 2) defining a numerical value (and underlying that is the units). So I can click on a line & select 1.25. If current units are inches, it is now exactly 1.25 inches. (Side note, if I type 30mm in the dialog box, SW does the conversion calculation on the fly & display shows 1.1811" because we are working in inches. Alternately I can select the 2 line end points on a line & do the same thing. Other geometry works the same way, radius, diameter, inscribed circle of a polygon, nodes of a spline.

Next, lets say I start drawing a sketch & insert a line segment like above. I click-click 2 points. The left parameter panel says is just so happens to be 1.2345" long. But the line color is blue which corresponds to as of yet undefined. Now if I 'dimension' it to 1.000" the properties panel dutifully reflects this change & updates to 1.000". Which is exactly how this process is supposed to work. The initial sketch (blue) is essentially freehand. Get the profile roughed in, then go back & (ideally) fully dimension it. Element by element they turn from blue to black meaning fully defined. This goes a long ways to preventing problems down the line.

Everything I've said thus far has to do with dimensions, or dimensional constraints - as opposed to geometric constraints which means for example make this line perpendicular that line, this circle tangent to that point, these 3 lines equal length, those 2 lines colinear... As mentioned you can have permutations of fully/non constrained dimensions & fully/non relationships. But ideally its considered best practice to have fully defined 'both'.

But backing up to the example, what's going on? SW is actually making an intelligent guess when you first sketch. That's why they use the word sketch which infers somewhat loose outlining, step-1. It knows the rough line was 1.2345" long because underlying this process is the Part model template you have pre-selected or allowed it to default to before beginning a new part. That template specifies a whole host of custom initialization parameters which is another topic. So probably we have an IPS (inch/pound/second) template chosen as opposed to MGS (millimeter/gram/second from memory). For example I could have chosen a different template for designing a pipeline where default length was km (kilometer) & SW would have guessed the line was 1.234 km long.

So to recap, the template dictates the underlying units & initial screen scale if you want to think of it like that. When you start making elements, they really do have a physical dimension associated with them as evidenced in the properties panel. But if you 'define' the dimension which shows as the classic arrows or callout of the sketch, the properties reflect that change. They are one of the same. Similarly if I overtype 2.00" in the property panel, the displayed dimension will update from that accordingly. But panel & dimension serve slightly different purposes which is probably a source of confusion in these discussions.

Now if you leave the dimension as the undefined initial guess (blue) SW will try to extrude or cut or do whatever feature is being called upon. If the geometry is compliant, it will succeed. The reason why it works most times is because it uses the 'rough guess value' in the absence of a defined value. The whole idea of modelling is you can go back & alter that dimension & everything downstream updates correctly.

So what @GreenTwin is doing is circumventing SW sketch process & importing essentially the same thing from a different 2D modeler. So if he defined 1.000" in ACAD, SW respected that & made the line 1.000" long as evidenced by the properties panel. I'm actually interested to know if he selected an edge & dimensioned inside SW would the dimension show (light grey) 1.000"? Light grey is SW way of saying a byproduct dimension which comes as a result of other defining dimensions. For example measuring the diagonal of a rectangle as an FYI is grey vs the sides are defined dimensions & therefore black. Now if @GreenTwin left the dimensions undefined and/or the geometric relations undefined, SW would respect that no different than leaving it dangling if sketched entirely within SW.

There may also be SW nuances of this importation method that still leave a sketch blue / undefined. If he fully defined a 1.000 x 1.000 square & geometric perpendicular references in ACAD & imported it, SW is picky of where entities are relative to its global space (important for reasons I'll leave for now). The square may also be blue until you make a corner coincident to XYZ reference 0,0,0 datum. It would then turn from blue or partial blue to fully black. The exact same thing would happen if drawn entirely within SW.

BTW I have never heard anyone saying the importation method wont work, or the model blows up. Obviously it works.. for now at this level. There are analogous examples of other types of importations which are not native to SW, mesh files as I mentioned. But it is considered 'best practice' to work within the SW sketch/feature cycle.

 

[Jasonb]

Seems you also use the term Dimension Peter

And what you say is just how Alibre works except it does not have the dropdown box you mention Just clicking the mouse produces a random line but I can enter a dimension between clicks, select the line and enter a dimension or select the two end points and enter a dimension. Only if a line in a sketch is driven can I not directly enter a dimension but can only make that change buy editing the other elements dimensions that drive it.

 

[petertha]

I'm pretty sure SW allows you to enter a dimensional value on the fly as well, at least line drawing if I recall. Click start point, direct mouse out in space at some orientation, it rubber bands, enter keyboard value 1.234", it sets the point down at that length. There could be options in the properties area that control this on/off. There are tons of things like that which are user preference.

 

[GreenTwin]

I have actually never noticed the sketch changing color, other than when I pick a line or entire sketch, it does turn a bright blue.
I specifically got Solidworks for its sketch import capabilities, given my use of Autocad, and also because SW had a one-time price, with no yearly fees.

I can't really discuss fully defining a sketch since I ignore that function.

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[Jasonb]

That' it.

Just thought of a 4th way, it will snap to a grid though I don't ever have the grid on so don't use snap to grid.

 

[GreenTwin]

I recall when I started learning Autocad 100 years ago (seems like that long), the books said it is "Critical" to first set the "limits".
I have never set the limits on any drawing, and never have for 30 (+) years.
Not must be too critical I guess.

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[Richard Hed]

I think it is a Tower of Babel thing to some extent, but people ask for free help here, and I try to give it.
I think we need to really use global terms, since most of use don't have multiple 3D programs, and we don't necessarily know the differences between all of the 3D programs.

Best I can do really is share concepts.
Others will have to translate that to their 3D program; I can't do that.

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Since Gordon is testing out Alibre, you should maybe only refer to Alibre terms and techniques.

 

[GreenTwin]

Since Gordon is testing out Alibre, you should maybe only refer to Alibre terms and techniques.

Aye, but there is the rub, I have no idea what Alibre terms and techniques are, so that is not possible.

But I did split the topic out and created a new topic here, so as not to distrupt Gordon's original thread.

This is a new topic with new discussions, and no limits on any discussion, and so anything goes here (we run with scissors in this thread).
This thread is for concepts that can be applied to any 3D program or user.

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[GreenTwin]

I think it is safe to say that there is dimensional data, which may or may not be associated with dimensions that are visible on the screen.

And there is dimensional data that is associated with sketches, and parts of sketches.

But I would not say that dimensions data is the same as visible dimensions on the screen; that would not be true.

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[GreenTwin]

I have a Prusa 3D printer, but the things I talk about with 3D printing are not limited to a Prusa, and would most likely apply to anyone using any 3D printer.

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[Richard Hed]

Aye, but there is the rub, I have no idea what Alibre terms and techniques are, so that is not possible.

But I did split the topic out and created a new topic here, so as not to distrupt Gordon's original thread.

This is a new topic with new discussions, and no limits on any discussion, and so anything goes here (we run with scissors in this thread).
This thread is for concepts that can be applied to any 3D program or user.

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Get a 30 day trial copy and test it out. Take it for a drive on I-90 , pass Moses Lake, collect 200$

 

[petertha]

I recall when I started learning Autocad 100 years ago (seems like that long), the books said it is "Critical" to first set the "limits".
I have never set the limits on any drawing, and never have for 30 (+) years.
Not must be too critical I guess.

I remember that. Well vaguely. I think one flavor was memory / processing based in the good old days. The other was some kind of pre printing rigmarole.

But your experience of never having an issue may be related to your file sizes always being comfortably under the deemed limit where instability occurs. Presumably the software engineers got the butt end of customers screaming at them that their file blew up & had to do something about it. (or maybe it was some kind of processing algorithm that speeded up calculations & refresh, who knows). Either way it was in their interest to come up with some kind of fix to proactively warn you or prevent worse consequences.

https://www.quora.com/What-is-the-necesssity-of-setting-limits-at-the-beginning-of-AutoCAD

 

[johnmcc69]

I don't agree with many things mentioned here. But as Pat mentions, everyone has their "method".

My opinion is this: 3D CAD is a great tool. & with over 25 years of using it "professionally" designing "Things" (industrial, medical..) & as a hobbyist modeling/designing engines, I have not come across many instances where I had to import 2D sketches to create my geometry in 3D CAD, or any other data unless it might have been a customers photo they wanted in a drawing. In EVERY 3D CAD project I've done (Tooling, ETC., or model engines), I've always done it in my 3D CAD program. Just using one software tool (Database) & have never had to worry about keeping multiple documents current. (I know we're talking model engines at the "hobbyist" level, but I have to mention these things..)

Mentioned earlier (In this thread or another) Pat mentions what "works" for him, but I respectfully disagree with his methods in using 3D software, it seems (as I mentioned before, "counterproductive".)

A couple examples:

After "exporting" my CAD data into another program, I lose all associativity in my drawings & models. That creates many problems, for instance, (mentioned earlier, Pats drawings were created in ACAD). I lose "control" of dimensions, drawing views, sections, BOM's...) If I need to add a note to a drawing, change a Rev. level on a drawing format, I only need to change the ONE defined format of the drawing. If I created my drawings in ACAD, I would have a hell of a time going through all the drawings & cutting/pasting all the updated info into all the different drawings. (I once made a spelling mistake on a package of drawings & only had to edit the ONE drawing format).

BOM's: become unassociative after exporting to ACAD. If I change a fastener size, or add some, I lose my "connectivity" with my model/assy. God forbid if I have to manually edit my BOM"s, part no. balloons, that's a bitc$h).

If I have to add a part to the assy., or modify the shape of a part, I have to (Ughhhh) export all the drawings all over again. This affects all the assembly, section, & exploded views & once again disconnects all my data & requires me to update all my drawings. Painfully.

The method (ACAD) mentioned above is not the way 3D modeling is intended to work. & as Petertha has mentioned about sketching techniques, "But it is considered 'best practice' to work within the SW sketch/feature cycle."

After creating my drawings (In a 3D package), all I do is "Print to PDF".

https://www.homemodelenginemachinist.com/threads/maudslay-brass-steam-engine-drawings.30809/


But hey, "Whatever works for you".

 

[petertha]

@GreenTwin I wonder if you are aware of this SW functionality example. I started a very simple sketch within SW. It has some dimensions defined thus far, but still has some blue lines so not fully defined. As my picture notes convey, its very easy to see what's going on with active feedback. I just grab a line element. If it doesn't move, it means its constrained (dimensionally and/or by virtue of relationships). If it can move, it expands or contracts or changes in the orientation that is still free & floaty. So you say aha & define that dimension or relationship.

Now if you don't mind, can you try that in one of your imported sketches. Is this SW diagnostic feature essentially locked into whatever you imported?

 

[petertha]

Example of SW defined (black) vs derived (grey) dimensions. Derived dimensions may be of interest for other purposes, but you may still want to select certain specific dimensions to define the shape. Completely inside of your control. You can display any number of derived dimensions. You can change you mind, delete a defined dimension & select another if it makes more sense. All of this visual feedback is happening real time.

Also if a sketch becomes dimensionally over-defined (or other problems) not only does it tell you with a warning before invoking a feature, you can launch a debugger & pick from a SW generated selection list of 'which of these fixes would you like to apply' because there could be many possibilities but only one that you prefer. It doesn't solve horrible geometry but catches 90% of obvious issues. Without the benefit of dimensions being shown, color coding, real time feedback, it curtails the capabilities of the software. By importing bad geometry, you have no similar feedback inside the sketch if there is an issue until the feature blows up. This is just scratching the surface but hopefully helpful.

 

[Bentwings]

sorry I got interrupted
I think it is a matter of terminology, and the terminology in 3D modeling is very confusing for me, and confusing for others too I think.

3D modeling is a database.

If I draw a line on a sketch in a 3D modeling program, the program creates a set of data for that line, which is start point, end point, length, and angle.
Also perhaps color.

If I add a dimension to that line in 2D Autocad, that dimension is for display only, and no data in the database for that line changes just because I added a dimension to it.

If I add a dimension in the 3D modeling program, I can "drive" the line database using the dimension as an input tool.
The dimension can define and dynamically control the line.
I can delete the dimension, and not change the line's database if I have not used the dimension "drive" function.

There is no need to fully constrain anything in 3D modeling unless you do something that requires a fully constrained sketch.
I have never constrained anything in 3D, as far as doing any additional steps after importing a sketch from Autocad.
You may want to fully constrain a sketch in 3D, but I am living proof that you can also totally ignore constraints as far as adding extras to an initial sketch.


I think you have to think of it in a database format, as I mention above.

Think of it as a spreadsheet.
You can think of the sketches I do in Autocad as just some dumb valve like "A" that has been typed into a spreadsheet cell.
"A" does not do anything, and is not linked to any other cell in the spreadsheet.
I can copy or move "A's" around in other cells, and it does not affect anything.
"A" is just a dumb valve with no links or formulas.

If I type in the number 1, then I can start to program other cells, such as cell #2 equals two times what is in the first cell.

When you start adding driving dimensions and constraints in 3D modeling, you are basically programming the database to say "When I change this, these other things are linked so that things happen automatically".

So the analogy is that I use a spreadsheet with dumb input valves, with no formulas, no links, no programming of any type.
You can't say spreadsheets don't work unless you program all the cells; this is false.
You can just punch numbers and letters into spreadsheet cells, and it is all good; nothing is linked to anything.

I think we are talking circles because of terminology.

Talk about the initial data table created for each line or shape (creating a sketch).

Then talk about automating the optional connections between the various values in the data tables (adding constraints).

Then talk about adding optional driving dimensions to further constrain a sketch, and automate the sketch (like adding forumlas to a spreadsheet cell).

I use the dumb method.
It works very well, it is very simple, and since I design and draw (created sketches) very accurately in Autocad, it is a very fast method for 3D modeling for me.
I rough out the initial overall engine geometry in 2D Autocad before I start any 3D modeling.
I don't try to make things work in 3D modeling, I work out the geometry in 2D first, and then 3D modeling is just a visual representation of the 2D geometry.

If you can get value-added function from using additional constraints, driven dimensions, etc., more power to you, but that slows me down a lot.

In spreadsheets, I get very sophisticated, and use look-up tables, extensive Visual Basic programming, popup dialog boxes; you name it.

How sophisticated I get with any given program depends on what I am trying to do, and what is the fastest and most efficient way for me to do it.

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im kinda lost here . I’ve been through so many cad programs over the years I remember goingvto an auto cad seminar when it turned out it was noting but an electronic drafting board . I had already benn in solid modeling for a number of years . I even ran and serviced the mini computer and work stations . I could not believe the “ monkey business “ this was. Essentially you created a drawing with a stylus pen A week or so later the sales rep came to see what we thought of his system I gathered the other cad people to my cubicle then Since I had a paper copy of his drawing I did a watch this thing . I recreated it as a solid model then I said how big would you like to see the paper drawing , pick a scale factor I’ll put at least had a dozed views including s broken section up too then I had each of our crew add some features
I can only state why this works for me.
It works well for me because I find the sketch tools in 3D programs to be very slow, inefficient, and totally inadequate for what I do, and how I do it.

The sketching tools that come with 3D programs are quite adequate for most folks.
I am not "most folks".
And I can speak from 10 years of using this method (sketching in Autocad and importing to Solidworks) to make a lot of complicated models, so I am not just speculating, but rather speaking from experience.

Everyone should use the method that turns them on, and the method that works for them best, and stop worrying about whether someone else's method is different, or if that method conforms to the norms, or is or is not "like everybody else is doing it".

There are many ways to do everything.
Let the users decide what works best for them.
Tell them all the options, and let them decide.
I don't see the downside to this.
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