[SOLVED] Making a hole in a non-flat surface

[tyszja]

Hi,

May I ask for the right approach to making a hole in a non-flat surface? On a flat surface I would go with the sketch and pocket but for a non-flat surface I went with the boolean operations. However these seems to fail from time to time and no hole is being made by the 'Cut' operation. I can't seem to figure out what did I do wrong? Some holes are being done the right way and some not.

I've attached the blower fan tryout project file with a bunch of beams cutting a square holes in a fan duct thing. You would notice that some boolean operations went right, one failed, and if you apply a boolean operator on any of the outstanding ones, it will fail.

I'm using Part Design WB and Freecad 0.19 own (git) build. (Due to Ubuntu Snap App version failing on GL Context creation, but anyway that's not the problem as my changes are only in GUI part.)

I would appreciate any help or hint on the best approach to this.

[SOLVED]
Solution proposed by chrisb was the one that worked. Part Design WB has 2 flavors of boolean operations. In this design the 'Substractive Primitive' was the right one and the classic boolean was failing.

[meme2704]

hi
You complicate the job by drawing 12 times the same cube, while an Array is enough, but you have to go through Draft (Multitransform maybe )
and I imagine the rest by transforming cubes into pipes

[tyszja]

Hi meme2704,

Thanks for posting your file. It's not exactly what I was aiming for though. These radially placed cubes were just made to cut the the square holes in the big crescent shaped part and not to become pipes themselves. But I guess your approach might help me to achieve what I need. I admit I'm still a noob who's limited to few known functions of FreeCAD. I'll take some time exploring functions you've used in your approach. Thanks a bunch.

BTW: I might have overcomplicated the design but it does not explain the failing boolean operations. In your approach one of pipes seems broken as well.

[EDIT] Nah... Boolean's Cut with an array make the whole crescent shaped body disappear completely.

[chrisb]

CheckGeometry with BOP Check enabled shows self intersection errors in the Body. I guess you have some coplanar faces. Sorry, I have no more time to investigate this further.

[meme2704]

Indeed, by opening my file I discover an error, which causes a fatal, I do not know where
I correct it by changing the method

[chrisb]

Cube003 with Boolean003 caused the error, although I don't see why. The proper PartDesign way of doing this is not to use boolean operations (explicitely) at all. Part design features have built-in booleans: if you make a pad it is fused immediately to the body, if you make a pocket it is immediately cut.

The proper way would have been to use pockets or subtractive cubes. I used the latter in my example,

Bildschirmfoto 2019-05-25 um 19.00.36.png (22.35 KiB) Viewed 378 times

because it resembles your approach directly in PartDesign. I have replaced Cube003, so you can verify that the cubes are the same, then I added a polar pattern. You can increase the number to get more holes or you can reuse the positions of your fancy placed cubes.

[tyszja]

Thank's chrisb. It seems that the substractive primitive is the way to go with this one. It's hard to find the 'proper way' of doing things when you are given a bunch of tools to do it the 'wrong way' and one that will actually work.

I'm still amazed how some fairly complicated parts can be done quite easily with FreeCAD and still a simple thing like a hole can become a problem. The boolean's cut can be done in like 5 ways (multiple workbenches having their own boolean flavor which behaves differently from others) and 4 of them can fail in your design but still work fine in other designs. Thanks for your time guys/gals.

[chrisb]

You're welcome. If you see this forum as part of FreeCAD, then FreeCAD is a wonderfully documented system.

[vocx]

...
It's hard to find the 'proper way' of doing things when you are given a bunch of tools to do it the 'wrong way' and one that will actually work.
...

Don't think this is a problem with FreeCAD in particular. Every CAD program has this characteristic that there is more than one way to achieve the same result. A CAD program gives you many tools to work with 3D objects, but you need experience using them to develop a workflow that works for you.

[tyszja]

Don't think this is a problem with FreeCAD in particular. Every CAD program has this characteristic that there is more than one way to achieve the same result. A CAD program gives you many tools to work with 3D objects, but you need experience using them to develop a workflow that works for you.

I would agree with you If I could actually achieve the same results. Don't take me wrong, I think FreeCAD is a great tool for a FOSS but there is a reason it's still on 0.xy version. If I could achieve the same results using boolean operator which works differently on each workbench I could only complain about the bad UX or inconsistent design (which is not uncommon in community driven software). Instead it's like having different hammer for each type of nail you use, and only one combination of nail and hammer will ever work. That makes a simple nail hitting (boolean cut) job harder. You would be more productive having a single hammer that you can rely on in every nail hitting work.

Regards.