3D cad question

[Jasonb]

In which case you are using constraints and dimensions. I'll do a video a bit later of something simple like a steam chest cover, one constrained and dimensioned, the other just freehanded with the mouse. Then I'll make a couple of alterations to the sketches and you will see why you DO want to use them rather than saying don't use them.

In the mean time a quick question, if you wanted to start a sketch off with say a rectangle, do you sketch 4 lines or use the rectangle tool?

 

[Richard Hed]

But the circle is still 1, and I don't need to lock it because I have never had anything move.

If its not broken, don't fix it.

Perhaps good practice, but entirely unnecessary as far as I can tell with all the engines I have modeled.

When you draw a circle, do you initially draw it at 1, or do you drive it to 1 using the dimension, or drive it to 1 with a dialog box?
Seems like you really only need to define it as 1 once, not twice.

Have you tried making sketches without dimensions?
Does making sketches without dimesions cause things to shift in Alibre?

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Do you have AutoCAD 3D?

 

[Oldiron]

I'll do a video a bit later of something simple like a steam chest cover, one constrained and dimensioned, the other just freehanded with the mouse. Then I'll make a couple of alterations to the sketches and you will see why you DO want to use them rather than saying don't use them.

Jason, anxiously awaiting. Bob

 

[Jasonb]

I've put the video into the constraints thread as it's more applicable.

https://www.homemodelenginemachinis...s-dimensions-in-3d-modeling.34573/post-386972

 

[GreenTwin]

In the mean time a quick question, if you wanted to start a sketch off with say a rectangle, do you sketch 4 lines or use the rectangle tool?

If I am in AutoCad, I draw a rectangle, because I often stretch those, and want them to remain a single entity.

In Solidworks, I offset one at a time from the central axis; so four separate lines.

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[GreenTwin]

Do you have AutoCAD 3D?

Solidworks

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[Jasonb]

The video shows why 4 separate lines is not a good option.

 

[petertha]

If I am in AutoCad, I draw a rectangle, because I often stretch those, and want them to remain a single entity.
In Solidworks, I offset one at a time from the central axis; so four separate lines.

SW is intending to save you time & pre-ensure the initial sketch entity has some minimal constraint which by definition is associated with that particular geometry.

A rectangle has 4 line elements, each connected, but opposing 2 are parallel & same length & all corners are 90-deg. What is left to be defined is up to you: 2 unique lengths & the angle that the entire rectangle may be relative to some other datum. ie. the base could be horizontal, or at 12.345 deg, it matters not. Drawing 4 lines & defining all those relationships is extra effort, more steps, more chance to make errors. Of course there are times when 4 lines makes sense & just so happens to look like a rectangle. You are free to do it that way too, whatever makes sense for purpose. But when a primary geometric shape makes most sense, best to leverage on that. Most CAD programs are similar but again SW sketch may have some nuances you haven't seen or leveraged upon yet.

This same thinking process is consistent in all other pre-built geometric features. For example a polygon. You just select a starting point & rough it in. All it knows for sure (by polygon definition) is that all sides are equal length & all internal angles are equal. Now the remaining defining features are up to you: what number of facets, inscribed vs circumscribed diameter, angle of datum which then rotates all other segments according. Doing this manually takes way longer.

This is why I was saying earlier, with this collection of SW geometric building blocks, there is nothing that ACAD or any other 2D package offers that can't be replicated entirely within SW sketch tools, arguably more efficiently once you get the hang of it. And doing so opens up many more possibility doors that tie into parametric designing. Whereas 'importation' kind of appears accomplish the same thing, but presents other potential limitations or disadvantages. Not trying to sell you to change your workflow to suite my personal opinion, but for anyone learning from scratch I would say stay within the SW fish tank for now

 

[GreenTwin]

Sketching in Autocad is like driving a car with an automatic transmission.
Using 2D in Solidworks is like trying to drive a car with a clutch and stickshift, if you have never driven one of those before.

I can drive either type of car, but one feels fluid, and one I have to think about.

The new folks will learn one program only most likely, which in the end I think will turn out better, but "better" may be the topic of much debate.
Different may be a better description.

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[petertha]

There is no sense debating this IMO. Your workflow works for your purposes & you are comfortable with it. Its a hobby for both of us. All is good. I would just say that its somewhat unconventional. I can envision a point or collection of circumstances where you may hit limitations or obstacles but thats outside the scope. I am no 3D expert but it seems like consistent mantra that the 2D sketching environment is internal to the package, not external. Even with Autocad's own products Inventor & Fusion 360 (although I haven't used either personally). The fact that 3D packages can cross link to other formats provides extra power & utility. For example most can import manipulate & export mesh files which is very useful in some instances, but the typical CAD apps we use are not a mesh/facet modelers like Blender or Zbrush. Different animals in the same zoo.

 

[johnmcc69]

Another great topic!

IMHO, not using constraints is totally defeating the purpose of using 3D cad.
https://www.homemodelenginemachinist.com/threads/3d-cad-design-sequence.34574/page-3#post-386997
It's all about "relationships" between all the parts... & working in unison.

John

 

[GreenTwin]

There is no sense debating this IMO.

I don't see it as a debate per se, but rather a comparing of notes about how each individual does their 2D and 3D modeling.
And as I mentioned, I often use a hyrid of approaches, mixing and matching, and often abandoning one approach if I find a better approach.

I am not married to any one method or system, but I just use what is fastest and easiest for me at the moment.

I like to understand how others are doing 2D and 3D, because there is a lot to it, and I understand that I have a lot to learn, and will certainly never learn all their is to know.
.

 

[johnmcc69]

A bunch of ways to skin a cat....

But what you say is true, we're all here to learn about different methods, whether its's CAD or machining. It's all good information.

John

 

[petertha]

I don't see it as a debate per se, but rather a comparing of notes about how each individual does their 2D and 3D modeling.

Totally agree. I should chosen a different, softer word. I just mean pros & cons.

 

[GreenTwin]

In the foundry world, people get into raging debates about which burner type is best.
It is a Ford vs Chevy type discussion, and typically ends with a lot of eye gouging and bloodletting.
God forbid you should mention HEMI.

The best burner is the one that works best for YOU.

Of course if you ask me, the sipon or its cousin the pressure nozzle are the only burner types any sane person would use, but where is it written that you have to be sane to do foundry work?
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[Richard Hed]

Sketching in Autocad is like driving a car with an automatic transmission.
Using 2D in Solidworks is like trying to drive a car with a clutch and stickshift, if you have never driven one of those before.

I can drive either type of car, but one feels fluid, and one I have to think about.

The new folks will learn one program only most likely, which in the end I think will turn out better, but "better" may be the topic of much debate.
Different may be a better description.

.

I disagree. AutoCAD is like trying to drive a train on a small country town main drag. Powerful but hard to do. I've used it for many years. But I'm not talking about sketches.

 

[GreenTwin]

These days, many firms are using building models.
The building model is only as good as the folks inputting data into the model.

For large multi-discipline designs, the building model can be both good and bad.
Its good in that you can pull up a 3D model of the entire building/structure, and walk through it virtually, and really get a feel for things.
The bad side is that people tend to be like messy teenagers, and they leave fragments everywhere, and don't keep their models clean.

I have always said that if I ever have to do a large project using a multi-discipline building modeling, I would retire rather than do that, but I am in the middle of one now, and it is a bit of a tar baby. I won't make the mistake of doing another work project in 3D.
Luckily most of my work can easily be done in 2D.

It is hard to do occasional 3D modeling.
You have to do a certain critical mass of it in order to get proficient with it.

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[johnmcc69]

I think all this might be going over the top for the original question posted by Gordon. (Although, it is some really good insight to 3D CAD). It's definitely a big shift from working in 2D ACAD (Which I still use all the time & don't under estimate the power of "paperspace" & using viewports).

Gordon: What version of Alibre are you using & what specific type of part are you trying to create? I'd be willing to bet that Jason B. will walk you through it. He's pretty good with that program & I don't doubt that he would would help you out (He likes a challenge).

Maybe you could share a drawing of what you're trying to accomplish with the part you're working on? It also might be interesting to find out how everybody may create that (never stop learning!).

John

 

[Jasonb]

Gordon Why not start a thread on "designing an engine with Alibre" or some such title, put a link to the engine plans you are drawing and suggest a couple of parts you would like to see drawn preferably not starting with the crankcase!

John, he is using Aton 3D trial.

 

[Bentwings]

well that’s just great, I got a phone call and my whole reply disappeared . I’m not going to redo it now maybe later
I think all this might be going over the top for the original question posted by Gordon. (Although, it is some really good insight to 3D CAD). It's definitely a big shift from working in 2D ACAD (Which I still use all the time & don't under estimate the power of "paperspace" & using viewports).

Gordon: What version of Alibre are you using & what specific type of part are you trying to create? I'd be willing to bet that Jason B. will walk you through it. He's pretty good with that program & I don't doubt that he would would help you out (He likes a challenge).

Maybe you could share a drawing of what you're trying to accomplish with the part you're working on? It also might be interesting to find out how everybody may create that (never stop learning!).

John