Section view hatch without a rib

Discussions about the development of the TechDraw workbench
Forum rules
Be nice to others! Respect the FreeCAD code of conduct!
User avatar
NewJoker
Veteran
Posts: 3018
Joined: Sun Oct 11, 2020 7:49 pm

Section view hatch without a rib

Post by NewJoker »

Hi,

I modeled a body of a fancy clothes hanger, following a YouTube tutorial. The problem is that I want to create a section view but with no hatching where the rib is (according to the technical drawing rules, ribs shouldn't be hatched):

rib hatch.PNG
rib hatch.PNG (53.39 KiB) Viewed 2788 times

Of course, I can disable hatching for the entire section view but then how can I apply hatch to the desired faces without doing it for a rib ? Is it even doable considering the fact that sketching in TechDraw is not yet supported (it could be really helpful here) ?

Clothes hanger body.FCStd
(430.37 KiB) Downloaded 48 times
Workshop_Notes
Posts: 590
Joined: Wed Sep 29, 2021 8:35 am

Re: Section view hatch without a rib

Post by Workshop_Notes »

NewJoker wrote: Tue May 24, 2022 9:50 pm (according to the technical drawing rules, ribs shouldn't be hatched):
What rules are you relying on here?

Is there not also a greater rule that says anything cut through by the section line should be sectioned? And that is what TechDraw is doing.

Scribble on your sketch in MS paint where you think the hatching should start and stop and also any kind of line that you might want to separate the hatched and non-hatched parts. Then try to translate that into a general method that can be programmed into a dumb computer so it can do the same, correctly, every time.

If you want the rib to be unsectioned, you would have to use a joggled/zig-zag section line.

For example, see: https://www.youtube.com/watch?v=Dg2szQ3xpAw

Same thing but the pictures are not moving: https://forum.freecadweb.org/viewtopic.php?f=3&t=51249
User avatar
NewJoker
Veteran
Posts: 3018
Joined: Sun Oct 11, 2020 7:49 pm

Re: Section view hatch without a rib

Post by NewJoker »

Workshop_Notes wrote: Wed May 25, 2022 6:48 am What rules are you relying on here?

Is there not also a greater rule that says anything cut through by the section line should be sectioned? And that is what TechDraw is doing.
I use a classic Polish book "Rysunek techniczny maszynowy" by T. Dobrzański as a reference. Here's a translated quote from this book:

In the case of views of sections passing through object's walls, ribs or spokes, those features are drawn in a view as if they were placed right behind the section plane.
Here's an example provided in the book:

rib section view.png
rib section view.png (11.32 KiB) Viewed 2673 times

Workshop_Notes wrote: Wed May 25, 2022 6:48 am Scribble on your sketch in MS paint where you think the hatching should start and stop and also any kind of line that you might want to separate the hatched and non-hatched parts. Then try to translate that into a general method that can be programmed into a dumb computer so it can do the same, correctly, every time.
Of course, FreeCAD won't be able to recognize ribs and eliminate them from hatching automatically. I'm looking for a manual approach. But since it's not possible to sketch freely in TechDraw, that might be impossible.

Workshop_Notes wrote: Wed May 25, 2022 6:48 am If you want the rib to be unsectioned, you would have to use a joggled/zig-zag section line.

For example, see: https://www.youtube.com/watch?v=Dg2szQ3xpAw
I was thinking about the use of this custom section view workaround but I'm not sure if it would work here. The thing is that I'd like the section view to follow the same straight line and just omit hatching for the rib. Maybe export to Inkscape is the only way to do this here.
user1234
Veteran
Posts: 3340
Joined: Mon Jul 11, 2016 5:08 pm

Re: Section view hatch without a rib

Post by user1234 »

NewJoker wrote: Tue May 24, 2022 9:50 pm The problem is that I want to create a section view but with no hatching where the rib is (according to the technical drawing rules, ribs shouldn't be hatched)
I do not know, if there is a commercial 3D CAD program out there, which can do that (with workarounds it is possible with commercial 3D CADs). They only can ignore whole parts (bolts, nuts, dowel pins, taper pins, .....) on sections. At the moment this is not possible with FreeCAD.


NewJoker wrote: Wed May 25, 2022 11:18 am Here's an example provided in the book
Looks like a breakout view.



If you need it, i would do a zig-zag section in 3D and make a 2D drawing out of it. But there are some issues with that.

1.png
1.png (47.43 KiB) Viewed 2653 times


- the face detection in FreeCAD is not the best. But wandererfan have made some improvements in that case, but as far as i know, it is not in the master atm, see https://forum.freecadweb.org/viewtopic. ... 80#p591838

- i wanted to refine as far as i can, but you have used very intensive external edges in the sketcher and generally not made TNP save. Since of that, i can not much do about that except make it completly new.

- generally, something like that, you should (constructive) avoid.

2.png
2.png (15.18 KiB) Viewed 2653 times


Generally asking, how is that made? If 3D printing, it would maybe work, but surely not in an other way (machining, molding, .....).


Greetings
user1234
Workshop_Notes
Posts: 590
Joined: Wed Sep 29, 2021 8:35 am

Re: Section view hatch without a rib

Post by Workshop_Notes »

NewJoker wrote: Wed May 25, 2022 11:18 am
In the case of views of sections passing through object's walls, ribs or spokes, those features are drawn in a view as if they were placed right behind the section plane.
Here's an example provided in the book:
As you say, it is easy for a human to know what a wall, rib or spoke is, but doing that in an algorithm is difficult, if not impossible.

If I were very critical, I might say that the extract from your book does not even follow his own rules. The vertical rib is indeed unsectioned, but what of the horizontal/flat part to the right of the hatching and below the rib? A small part of it is in section; the majority of it is not.

What is shown in the figure is what would be called a 'part section' (squiggly line at edge of cross hatching denotes section boundary) and on a partial view (note the squiggly break lines on the right hand side) at that. You could even argue that his section line is too long, and the two parallel, vertical bold lines should be much further to the left.

The whole point of 2D views is to present the 3D object as clearly as possible. You can have general rules to aid that but in the end, what is best printed on the page has to be determined on a case-by-case basis by the person wielding the drawing tools.

Please do try and mark up what you want hatched and what you do not want hatched and we can see how to achieve it. In your particular case, I would think a horizontal (plan) section, chopping off the top of the model (everything above the centreline of the blind hole) would convey the information equally as well as a vertical section.
User avatar
NewJoker
Veteran
Posts: 3018
Joined: Sun Oct 11, 2020 7:49 pm

Re: Section view hatch without a rib

Post by NewJoker »

user1234 wrote: Wed May 25, 2022 1:14 pm I do not know, if there is a commercial 3D CAD program out there, which can do that (with workarounds it is possible with commercial 3D CADs). They only can ignore whole parts (bolts, nuts, dowel pins, taper pins, .....) on sections.
In SolidWorks there's an option to exclude rib operations from hatching. But this is because SW has a special tool for easier creation of ribs. It could be also useful in FreeCAD but that's another topic.

user1234 wrote: Wed May 25, 2022 1:14 pm - generally, something like that, you should (constructive) avoid.

Generally asking, how is that made? If 3D printing, it would maybe work, but surely not in an other way (machining, molding, .....).
This part wasn't designed by me. I just recreated it based on a YouTube video. In fact, I did it because the author of that video said that he had to switch to another software since he wasn't able to obtain a proper section view with no hatching for rib in TechDraw.

The part was 3D printed by the author of the tutorial and serves him as a clothes hanger.

I don't link the video because it's in Polish.

Workshop_Notes wrote: Wed May 25, 2022 2:39 pm If I were very critical, I might say that the extract from your book does not even follow his own rules. The vertical rib is indeed unsectioned, but what of the horizontal/flat part to the right of the hatching and below the rib? A small part of it is in section; the majority of it is not.
Here are some examples from other books:

ribs.JPG
ribs.JPG (41.04 KiB) Viewed 2564 times
ribs 2.JPG
ribs 2.JPG (29.91 KiB) Viewed 2564 times

Workshop_Notes wrote: Wed May 25, 2022 2:39 pm Please do try and mark up what you want hatched and what you do not want hatched and we can see how to achieve it. In your particular case, I would think a horizontal (plan) section, chopping off the top of the model (everything above the centreline of the blind hole) would convey the information equally as well as a vertical section.
I will talk with the author of the video and ask him to send me what he prepared in that other software or at least mark what exactly he wants to achieve. I just want to know if it's doable in FreeCAD.
User avatar
NewJoker
Veteran
Posts: 3018
Joined: Sun Oct 11, 2020 7:49 pm

Re: Section view hatch without a rib

Post by NewJoker »

I recreated this model in SolidWorks. Here's how it looks like when the rib operation is excluded from hatching:

section without rib.JPG
section without rib.JPG (84.21 KiB) Viewed 2544 times

Can you think of any workarounds to achieve this effect in FreeCAD ?
User avatar
Shalmeneser
Veteran
Posts: 9475
Joined: Wed Dec 23, 2020 12:04 am
Location: Fr

Re: Section view hatch without a rib

Post by Shalmeneser »

Imho : "according to the technical drawing rules, ribs shouldn't be hatched"

Same idea as @user1234 : a cut object.

But a lot of problems hatching the cut :
* at the cut location
* with all fillets and chamfer.
Attachments
Clothes hanger body_SHALM2 (no techdraw).FCStd
(202.24 KiB) Downloaded 40 times
Capture d’écran 2022-05-25 220654.jpg
Capture d’écran 2022-05-25 220654.jpg (55.61 KiB) Viewed 2516 times
Clothes hanger body_SHALM.FCStd
(342.38 KiB) Downloaded 38 times
Capture d’écran 2022-05-25 221036.jpg
Capture d’écran 2022-05-25 221036.jpg (46.25 KiB) Viewed 2516 times
Workshop_Notes
Posts: 590
Joined: Wed Sep 29, 2021 8:35 am

Re: Section view hatch without a rib

Post by Workshop_Notes »

OK, here's a slightly unrelated question: why, in both the FC and SW drawings above, do they show solid lines at the tangency lines of the fillets? Do these appear if you print the drawing on paper?

If you look at the view of the angle bracket in an above post, just below the n) , there is no line where the rib joins the vertical surface (and the curves denoting the projhection of the vertical fillets either side of the rib just peter out). This is what I was taught as the correct way to show a face that blends into another face with a smooth transition. You only draw a line if it is an edge and a line of tangency is not an edge.

It is very difficult to make the artistry of good draftsperson into a procedure that the computer can do.

The first of the simpler examples shown could be reproduced in FC by offsetting the cutting plane just over half the width of the rib to the front. Note that the examples itself does not show a section line - we assume it is on the centre of the part.
user1234
Veteran
Posts: 3340
Joined: Mon Jul 11, 2016 5:08 pm

Re: Section view hatch without a rib

Post by user1234 »

NewJoker wrote: Wed May 25, 2022 5:47 pm This part wasn't designed by me.
Was not addressed to you, next time i try to address it better.

NewJoker wrote: Wed May 25, 2022 5:47 pm In SolidWorks there's an option to exclude rib operations from hatching. But this is because SW has a special tool for easier creation of ribs. It could be also useful in FreeCAD but that's another topic.
I have seen some CADs with rib functions (but they are not good), but never with an exclude in the 2D deviate. Interesting.


Shalmeneser wrote: Wed May 25, 2022 8:14 pm But a lot of problems hatching the cut :
* at the cut location
* with all fillets and chamfer.
Smart, some fillets and chamfers are missing in the section (marked some, not all), but the in the workflow you provided, it can easily added.
0.png
0.png (116.82 KiB) Viewed 2391 times

Workshop_Notes wrote: Thu May 26, 2022 7:25 am OK, here's a slightly unrelated question: why, in both the FC and SW drawings above, do they show solid lines at the tangency lines of the fillets?
Only for existing views:
Mark View --> Properties Tab --> Data --> HLR Parameters --> Smooth Visible (or others you like) --> false

For generally new views: Menu --> Edit --> Preferences --> TechDraw --> HLR --> Show Smooth Lines (or others you like) --> uncheck (or check others you like)


Greetings
user1234
Post Reply