Cut one object out of another which is rotated

[GregIthaca]

This seems like it should be a basic thing to do, but after 2 hours and poking around for tutorials and other posts, I haven't come up with anything. My basic request is as outline in the subject, but I can give a more specific example.

I want to have two parts/assemblies/whatevers. One is an I-beam. The other is a basic beam (rectangular) that intersects it at an angle and is cut out to fit around the I-beam. I don't have trouble creating something that looks like an I-beam. I can also create an object that is the other beam, and I can rotate the individual coordinate system for this object so that it's at the right angle. What I can't figure out is the cutout, because it's functionally at an angle to the beam.

1. I tried to figure out a way to just cut out one part from another part. This seems like the obvious way (I'm pretty sure this is how solidworks does it) but it doesn't seem like there's any way to relate parts to one another like this.
2. I tried using local coordinate systems in part design. All this seemed to do was to take ALL of the bodies in the part and rotate them. Thus, I could not get a BOX additive primitive and a BOX subtractive primitive that were at relative angles to each other.
3. I tried using the sketch tool to draw an outline of what I wanted subtracted onto the face of the beam. However, as soon as I go to try to apply the sketch it either breaks something (error messages about objects that aren't connected etc.) or it undoes the rotated coordinate system on the beam.

I can't really believe this isn't such a common activity that it's not supported, but I couldn't find any tutorials that did anything other than subtracting two objects (like a cylinder out of a box) that were in the same coordinate system.

[chrisb]

Hi and welcome to the forum!

Did you try the boolean cut in Part workbench?

[Willem]

If you want to built complex steel structures look at the "Dodo" workbench https://forum.freecadweb.org/viewtopic.php?f=36&t=38464

[bejant]

I can give a more specific example.

Hi, and welcome to the forum! If you do that, we can offer better help.

1. I tried to figure out a way to just cut out one part from another part.

There are several different ways in FreeCAD, depending on how you want to create your model.

it doesn't seem like there's any way to relate parts to one another

I can assure you that it is routinely done in FreeCAD models, but you simply haven't learned how to do that yet.

2. I tried using local coordinate systems in part design. All this seemed to do was to take ALL of the bodies in the part and rotate them.

I'm guessing that you rotated the whole Part container instead of rotating one Body inside the Part container.

3. I tried using the sketch tool to draw an outline of what I wanted subtracted onto the face of the beam. However, as soon as I go to try to apply the sketch it either breaks something (error messages about objects that aren't connected etc.)

What do you mean by "apply the sketch"?

it either breaks something (error messages about objects that aren't connected etc.)

What is the error message?

I can't really believe this isn't such a common activity that it's not supported

It's pretty common and is supported, but you just haven't yet learned how to do it in FreeCAD. Attached is an example model of what I think you want to do, but it's just a guess.

Extrude in the model is only an afterthought in order to visualize the shape of the 3D solid that creates the Pocket through the beam. Note that if the Sketch of the rectangular tube was a hollow, Pocket would have failed because it would have created two disconnected solids in Body, which is not allowed in the Part Design WB (it is allowed in the Part WB though).

I'm only back in the forum very briefly before I will be absent for some weeks again so I may not promptly reply back. There are many other very capable regulars who can help you along, and replies usually happen promptly, so don't poke around for 2 hours again before asking for help.

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OS: Ubuntu 18.04.3 LTS
Word size of OS: 32-bit
Word size of FreeCAD: 32-bit
Version: 0.18.4.
Build type: Release
Python version: 3.6.8
Qt version: 5.9.5
Coin version: 4.0.0a
OCC version: 7.3.0
Locale: English/UnitedStates (en_US)

[chrisb]

For a sort of temporary visualization aid you can very well use such an extrude, but please note that it creates an unallowed "link goes out of allowed scope", which show with a red arrow in the Std DependencyGraph. It is not allowed to reference something insede a body from a Part operation, so for a permanent solution you should use the whole body instead.
You can e.g. use a boolean cut between the objects: