Making lines for construction on an imported sketch

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lesthegringo
Posts: 19
Joined: Wed Nov 24, 2021 5:46 am

Re: Making lines for construction on an imported sketch

Post by lesthegringo »

I have tried it again (twice) today, and neither time worked properly. I followed the same procedure as yesterday, which was:-
Drawing the inner rectangle
setting the rectangle as symmetrical about the origin
setting the vertical side length
making the horizontal side length equal to the vertical converting it to a square
inserting the four 'preserve constraints' fillets, working clockwise from the top left corner
changing the radius of the filets to 5mm, working clockwise from the top left corner

The first time I tried it, it got to the bottom right radius and would not let me change that to 5mm giving an error (stupidly I didn't take a screenshot of that)

The second time worked better with no errors, but this time when I selected the 5mm radius in the top right corner it lost the equal constraint; yesterday it only lost the constraint when I did the last corner.

In each case I followed the same procedure, yet I got three different results. Looking from a point of view of pure logic that should not be possible, yet despite this that is what I am experiencing.

I'm as much confused as anything else!

Les
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chrisb
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Re: Making lines for construction on an imported sketch

Post by chrisb »

lesthegringo wrote: Fri Nov 26, 2021 5:59 am I have tried it again (twice) today, and neither time worked properly. I followed the same procedure as yesterday, which was:-
Drawing the inner rectangle
setting the rectangle as symmetrical about the origin
setting the vertical side length
making the horizontal side length equal to the vertical converting it to a square
Please upload the file just after that step, so we have the same for testing with all its constraints and orientation while building
The second time worked better with no errors, but this time when I selected the 5mm radius in the top right corner it lost the equal constraint; yesterday it only lost the constraint when I did the last corner.
In general it is not sensible to keep equality constraints, because in many cases they should apply after the filleting to the distance to the newly inserted corner points. Even that could be implemented, but it would be for my taste too much automatism, and your example shows that different constraining is pretty sensible.
A Sketcher Lecture with in-depth information is available in English, auf Deutsch, en français, en español.
lesthegringo
Posts: 19
Joined: Wed Nov 24, 2021 5:46 am

Re: Making lines for construction on an imported sketch

Post by lesthegringo »

Here's the file, I used the 'undo' feature to roll it back to the point requested so you have exacly what I started with; not sure if any error logs or suchlike is also saved though

I'm thinking of completely deleting my installation and reinstalling 'clean', as the fact that I don't get repeatable results seems more like a glitch than a functional issue - does that seem logical?

Cheers

Les
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onekk
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Re: Making lines for construction on an imported sketch

Post by onekk »

Bad habits are very difficult to leave.

Not to criticize, only to make some light.

Every CAD program has is own glitch, and there is no "a right way" to do things.

Things that are easy in a program maybe are dependant to the underlying engine.

FreeCAD is using OCCT engine, that have "his own set of rules"

See as examples as a simple tangency constraints of two circle is not so simple, see "Example of a Tangency Constraint" in this file.

https://dev.opencascade.org/doc/occt-7. ... algos.html

To show something that is not clear to many people, something, a mathematical formula will give you many results, and something, what is "natural" is not natural at all, "it depends" is the most useful answer to complexity.

depends of what?

is the following question.

This "what" is the key of complexity, once you have found all the "variables" maybe you will find that some other data are needed, or maybe you will find a completely different solution.

With FreeCAD if you decide to model a solid, you have many ways, CSG, BREP, or 2D shape creation + extruding in one direction.

as an example not exaustive, but if you use scripting, it is not "normal" that you have to extrude a thing in Z direction, so you have to supply a Vector.
ext1.png
ext1.png (4.63 KiB) Viewed 1287 times
But this vector will permit to make easily a slanted shape.
ext2.png
ext2.png (9.58 KiB) Viewed 1287 times
Only to point out something, that is usually misunderstood.

Many thing are derived from the way FreeCAD "3D modeling engine" modeling algorithm, and sadly this is not clearly understandable from the documentation.

As an example of some programs that uses this technology could be found in this page.

https://dev.opencascade.org/about/projects_and_products

If you have the patience to learn the way things are done in FreeCAD, it will be a very pleasant journey.

Las thing, FreeCAD worth much of the money you pay for it. Very much form my point of view.

Regards

Carlo D.
GitHub page: https://github.com/onekk/freecad-doc.
- In deep articles on FreeCAD.
- Learning how to model with scripting.
- Various other stuffs.

Blog: https://okkmkblog.wordpress.com/
TheMarkster
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Re: Making lines for construction on an imported sketch

Post by TheMarkster »

If you apply symmetry using the end points of the line segments, and then delete those end points with the fillet tool, then naturally the symmetry will be lost. Create your fillets first, then apply equality to them, and then apply symmetry using the the arc centers.
lesthegringo
Posts: 19
Joined: Wed Nov 24, 2021 5:46 am

Re: Making lines for construction on an imported sketch

Post by lesthegringo »

All, thanks for your answers and help on this.

However I have realised that for me (like Fusion360) trying to learn online and via Youtube videos and forums is going to be futile, as I can't ask at every step. I am going to look round locally for someone who can teach me face to face so that I have a way of interactively asking and seeing what to do.

If you are in Doha and are able to help me then please get in contact, but I will be putting an ad on the local help websites

Cheers

Les
chrisb
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Re: Making lines for construction on an imported sketch

Post by chrisb »

If you get a good tutor, that's the best you can do!
A Sketcher Lecture with in-depth information is available in English, auf Deutsch, en français, en español.
lesthegringo
Posts: 19
Joined: Wed Nov 24, 2021 5:46 am

Re: Making lines for construction on an imported sketch

Post by lesthegringo »

Thanks, I need somone to sit with me and explain the basics live, if I have to post a question every time I don't understand something or am not sure what to do, my first useable part will only emerge in the next century!

Les
chrisb
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Re: Making lines for construction on an imported sketch

Post by chrisb »

If you don't find someone, you may consider an onliine session. We use here in the forum from time to time jitsi meetings.
A Sketcher Lecture with in-depth information is available in English, auf Deutsch, en français, en español.
drmacro
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Re: Making lines for construction on an imported sketch

Post by drmacro »

chrisb wrote: Sat Nov 27, 2021 1:02 pm If you don't find someone, you may consider an onliine session. We use here in the forum from time to time jitsi meetings.
I've done online tutoring with Discord and Zoom as well.

Worked pretty good.
Star Trek II: The Wrath of Khan: Spock: "...His pattern indicates two-dimensional thinking."
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