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

[GreenTwin]

If a line happens to be at 89.895 deg because you inadvertently drew it that way, not orthogonal 90-deg the way you intended, how would you ever know?

But I just don't make mistakes like that, ever.
Solidworks engineers did not solve anything for me, I don't have a problem to solve.

And I think it is important to define "fully defined", "constrained", and "relation".
Since I don't use any of that I never think about it, but each has a unique function, or perhaps "fully defined" is the same as "constrained", or maybe not.

The relations which are so annoying for me can be demonstrated by drawing a line on the sketch plane, then drawing a few more lines.
Clicking on any line and right clicking to show the relations indicates that each subsequent line is related back to the first line.
You can delete those relationships, and this does not change the sketch.

But it is the very annoying relationships that cause me to do almost all of my sketching in Autocad.

Relationships may be designed to be helpful, but they are not, for me; they are totally counterproductive to the process I use in 2D to design engines.

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[GreenTwin]

In reality, the exact same thing is going on in Autocad but behind the scenes.

This is not true, because I can drag any line in Autocad without affecting any other line.

If I drag a line in Solidworks, it affects all the previous lines, and tries to drag/stretch them, which is a disaster.

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[petertha]

Solidworks assumes that when you offset, you want to offset everything on the screen, and that is never the case for me.
When I drag a line in a sketch, I never want that to drag/stretch every line on the screen; again Solidworks is making a false assumption to "help" me.
With "help" like that, who needs Solidworks? which is why I do most of my sketches in Autocad.

You have misunderstood SW flavor of offset. If you select a line & click offset, it literally does that. You optinally define the offset distance & side of offset. the beauty is you can do this same workflow to a line, arc, spline or complicated connected series of geometry. The trick is what you have FIRST selected before clicking offset. Its a timesaver but maybe you didn't realize the nuance.

If you want to draw line A & then another line B parallel to it at some as yet undefined distance, SW allows for that. You do it exactly as you would with paper & pencil. But notice what is happening behind the scenes by definition we said PARALLEL. So SW can populate this constraint between the 2 line entities & show that corresponding symbol in the constraints popup. Now if you change the angle of of A from 90-degto 35,5-deg, guess what, line B faithfully updates this relationship.

I know this stuff may sound clumsy & unfamiliar but once you get your head around that its just slightly different workflow, you will appreciate the power. Maybe this is a bad analogy but ACAD is like doing a freehand sketch, say like watercolor art. SW is more like drafting: T-square, angle protractor, scales... Math & geometry come together in a more accurate representation.

 

[GreenTwin]

SW does not constrain you in any manner

I think it is the relations that are causing me problems.
I don't constrain anything in Solidworks, and Solidworks does not automatically constrain anything for me, and so all is good.

The same cannot be said for relations between lines that I draw in Solidworks.
The program automatically creates relations that I don't want, and I have to go in and delete those, which is a lot of unnecessary work.
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[GreenTwin]

I know this stuff may sound clumsy & unfamiliar but once you get your head around that its just slightly different workflow, you will appreciate the power. Maybe this is a bad analogy but ACAD is like doing a freehand sketch, say like watercolor art. SW is more like drafting: T-square, angle protractor, scales... Math & geometry come together in a more accurate representation.

Solidworks is like having rubberbands connecting your pencil to your triangle, to your scale, to your protractor.
Move your pencil and everything else moves too.

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[GreenTwin]

You have misunderstood SW flavor of offset. If you select a line & click offset, it literally does that. You optinally define the offset distance & side of offset. the beauty is you can do this same workflow to a line, arc, spline or complicated connected series of geometry. The trick is what you have FIRST selected before clicking offset. Its a timesaver but maybe you didn't realize the nuance.

I need to read up on this.
I am not familiar with FIRST.

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[petertha]

This is not true, because I can drag any line in Autocad without affecting any other line.

If I drag a line in Solidworks, it affects all the previous lines, and tries to drag/stretch them, which is a disaster.

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This is because ACAD in this case has no initial sense of angle or geometry. It is undefined. Good for sliding around, bad for being specific as a member of a sketch model. And it will continue to be undefined until you do something about it, defining length & orientation one way or another.

Maybe we can arrange a video or something. I suspect it might be a setting or something you are doing or not doing causing this SW fuss.

 

[GreenTwin]

I think the bottom line is that it is much easier for me to create sketches in Autocad using the methods I have used for so many years, instead of learning a new method that is dintinctly different but accomplishes exactly the same thing.

That is what it seems like it boils down to.
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[Jasonb]

btw SW does not constrain you in any manner. If you really want to zing a line off at an angle, go ahead. The whole idea of sketch is literally 'sketch'. Get the profile looking visually about right almost in a freehand manner (step-1). All the lines are blue. Then go back & define the dimensions (step-2), now all the lines become black = confirmed fully defined. The relations aspect is kind of of an in-between thing, this line perpendicular to that line, this hole centered at that point, this fillet occurs between these 2 lines... But its an important thing as I showed in my example. You can have all the dimensions locked down, but if any number of relations are not correct, well simply, the part is therefore not correct. In reality that means the drawing dimensions will faithfully reflect this error you created & the part will not be machined correctly nor potentially fit correctly. Where is the fun in that?

That's much the same as Alibre, sketches are one colour when position and size is undefined but once you dimension them and tie their position down with constraints they change colour and won't be affected if you start moving other lines or shapes about.

 

[GreenTwin]

bad for being specific as a member of a sketch model

But I have never seen any problems with this, and have done it extensively.
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[GreenTwin]

That's much the same as Alibre, sketches are one colour when position and size is undefined but once you dimension them and tie their position down with constraints they change colour and won't be affected if you start moving other lines or shapes about.

I think the problem is that I almost always sketch in Autocad, and so I am not really familiar with what the Solidworks is doing when sketching.

I will have to go into Solidworks and draw a few sketches and play around with them.

But again, coming from a 2D Autocad background, I can say that there is very little need to do any sketching in Solidworks.
Just copy the sketch to the clipboard from Autocad, and paste it into Solidworks.
I keep Autocad and Solidworks open at the same time.

For someone who has never learned 2D Autocad, you could learn the sketch tools in Solidworks (or whatever 3D program you use) initially, and then you would know and understand how all that works.

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[GreenTwin]

I see this sort of like how do you cut an apple.
Do you cut at the stem, or cut along the equator, or radially, etc.
Perhaps no two people slice an apple the same way, and yet if you get the slices into the shape you want, the slicing method is somewhat (argueably) irrelevant.

I would like to understand all the implications of relations, constraints, etc.
The only thing that is clear to me is that I don't have a good understanding of them, and my workaround is to bypass all of that by sketching in Autocad.

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[GreenTwin]

It is quite interesting to compare notes with others using 3D programs to design model engines.

I got interested in 3D watching Brian Rupnow do it way back in 2011, and it was just something I had to learn.

I am glad everyone is sharing their ideas on what all the options are with 3D.

I learn a lot from every one of these discussions.
The feedback is very valuable to me.

I have always suspected that I am just touching the surface of what Solidworks is capable of doing.

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[GreenTwin]

I watched this video that Jason posted.

I can see how constraints could be useful if you took time to learn them.
I use Autocad every day, all day, and so for me it is better and easier to make sketches on that program and import to Solidworks.
I don't use Solidworks that often, and so if I learns all the constraints in that program, I would probably have to relearn them again if I did not use them much.


I find the grips in Autocad much easier to see and use than the ones that are in Solidworks.
I can easily change the size and color of the grips in Autocad.
I can snap ortho on and off in Autocad, to keep lines perfectly vertical horizontal, to draw at a random angle.
If I need a line at an angle, I draw it vertically, and then rotate it an exact number of degrees

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[GreenTwin]

You have misunderstood SW flavor of offset. If you select a line & click offset, it literally does that. You optinally define the offset distance & side of offset. the beauty is you can do this same workflow to a line, arc, spline or complicated connected series of geometry. The trick is what you have FIRST selected before clicking offset. Its a timesaver but maybe you didn't realize the nuance.

I played around with Solidworks a minute ago, paying attention to Relations.

I drew four separate lines, to make a rectangle (I did not use the rectangle function, but could have).
I picked one line only, and selected Offset, but it offset all four lines, which is what I am trying to avoid.

I picked one line, and then looked at was displayed in the dialog box on the left side of the screen.
It gives the following information for a LINE:

LINE:

Relations: (Horizontal, Vertical, Fixed)

Options: (For Construction, Infinite)

Parameters: (Length and angle)

Additional Parameters: (end point, delta X, delta Y)

So the line is defined in Solidworks, which is expected.

For the line I picked, the relation was horizontal.

One trick I tried is to draw an random line at an angle, select it, and then change the relation to horizontal.
The line snaps to the horizontal position.

OFFSET:

Next I played around with the OFFSET command:

I picked one line only, and picked the offset button, but all four lines that I drew offset all at the same time.

The options under OFFSET are:

Parameters: (add dimensions, reverse, select chain, bi-directional, make base construction)

Cap Ends: (arc, lines)

If "add the dimensions" box is selected, Solidworks will automatically draw in the dimension for you on the offset.
If the "reverse" box is selected, you will offset either inwards, or outwards.
If the "select chain" box is selected, you will either offset all the lines on the object all at once, or if unselected, you will only offset the one line selected, or perhaps if more than one line is selected, it will offset however many you selected.
If the "bi-directional" box is selected, it will offset one line inwards and a second line outwards, at the same time.
If the "make base construction" box is selected, the original rectangle that was drawn gets changed to dashed construction lines, which are not part of the sketch (Solidworks basically ignores any construction lines), and the new offset lines are solid.

If the "cap ends" and "arcs" are selected, and you are offsetting a single line, the ends of the original line and new line are closed with arcs.
If the "cap ends" and "lines" are selected, and you are offsetting a single line, the ends of the original line and new line are closed with straight lines.

So the "Select Chain" option is the one I need to toggle off, so I can offset a single line, and not get all the other lines trying to offset with it.


Solidworks has some powerful features, if you have time to dig into all of them, and then can remember all of that next time you use it.

The best way to really know a program is to use it every day.
I still have a lot to learn with Solidworks.

Autocad does not have a dialog box to show entity parameters, so I never think to use that dialog box in Solidworks to manipulate entities.
I always manipulate entities graphically in Solidworks, except for things line angle, or an offset value, which I enter into the dialog box.


If I pick one of the new offset lines, and look at the relations, it now shows horizontal, and also shows an offset relation.
So Solidworks is keeping track of not only the line parameters, but things like whether it was offset.

In AutoCad, you can drawing things like rectangles, or create blocks from multiple lines, and so you could call those relations between individual lines.
If you explode a rectangle in AutoCad, you get four separate lines that have no relationship to each other at all.
If you explode a block in AutoCad, then it reverts back to the non-related lines from which the block was created.

So I have solved my offset problem in Solidworks.

I wonder if I can change the size and color of grips in Solidworks.
That would be extremely helpful.

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[petertha]

I've taken a few screen grabs of various things discussed. Not trying to convince you to change. Just trying to show its just functionally different. Better or worse is in the hands of the operator.

Here is a random sketch just click clicking around. Shows with relations turned on & turned off. Think of it like an old school paper drawing. One is clean looking (no dimensions, nice art but basically useless for a machinist). The other is very busy looking because it has all those darn dimensions & angles & tolerances & scale &... It is busier looking because it conveying additional information, necessary for a specific purpose. But they are the exact same thing.

 

[petertha]

Drawing 2 lines in space. Because I ALLOWED them to be parallel, they ARE parallel. But I can freely move either around. And they remain parallel, which is the entire point of a constraint.

 

[petertha]

A slightly different 2 line variation. Maybe some of the issue you are experiencing. I draw 2 lines at what I consider oddball guesstimate angles to what my sketch will become. Remember a sketch is just a guess at this point. I have not assigned either lines dimensions. But notice in the parameters box to the left. It did in fact record the length & angle. ACAD does much the same thing behind the scenes, it just puts it in a different spot. Its there, but you just are not utilizing it in any meaningful way.

Now you cant grab either line & slide it as before like the parallel example. The nuance is yes you can. You grab the point at either end & swing it to a new position. then everything updates, the new length, the new angle

Remember a blue line (undefined) sketch is just a rough outline 'for now'. Its only when you assign dimensions & relations it becomes locked down & defined & therefore useful.

 

[petertha]

random single line, select it, click offset function, define offset amount, complete

 

[petertha]

make 3 random lines, select one line only. click offset, others remain as original