chrisb wrote: ↑Fri Nov 27, 2020 12:56 pm
Cossposting is not a very good idea. At maximum a link should do.
Ok, sorry, won't happen again. I did include a link to the original post, I just could not figure a way to link to my follow-up post to that.
uwestoehr wrote: ↑Fri Nov 27, 2020 12:57 pm
I did not quickly act because the question is why FreeCAD is not modeling the thread directly. What are the arguments?:
Pro:
* In other areas FreeCAD creates models as they will later be. This allows you to make everything with it, simulations, ray-traced views etc.
Contra:
* if you have a part with dozen threaded holes, creating objects for real threads makes recomputing slow
* the model tree is "polluted" with objects
Another con: norm conforming drawings don't need the actual threads, they need the an arc of a circle on the top view, and a rectangle on the section view. TechDraw would need to remove the thread geometry for this.
uwestoehr wrote: ↑Fri Nov 27, 2020 12:57 pm
So my current opinion is to:
- make the boring diameters norm-conform, but by default don't model the threads
- add an option to make the thread modeled as PartDesign object that appears in the tree
What are your opinions?
I think we're confusing things here:
Currently, threaded holes are no different from regular holes in either 3D view or TechDraw. My suggestion (based on the post I linked in my previous postt, it's worth checking the original thread, for the actual proposal from Maker with UI changes to the hole dialog) is to have the hole tool create one very simple symbolic 3D "fake" geometry to serve as the basis for both 3D view and TechDraw drawings: a cylindrical surface without top and bottom faces, that will be around the actual hole, and that will have a height equal to thread depth (not necessarily hole depth, blind holes are often not fully threaded). This fake geometry will have the following advantages:
- Serve as a visual hint that the hole is threaded in 3D view, since it will have a double ring around the hole. Currently there's no indication in 3D view that a hole is threaded, and the only way to see that is to find the hole operation that created the hole and check it's properties
- Serve as the rectangle required by the norm for TechDraw section view
- Serve as a placeholder for the arc that the norm requires around threaded holes once TechDraw is updated to support it. I know that TechDraw has some very fancy functions to add arcs around holes, but right now, I don't think they're used for this
I'm not knowledgeable enough about the inner workings of FreeCAD to know if this is a good idea, but it has the benefit of simplicity (all you're doing is adding a simple cylindrical surface around the hole, which should be very cheap compute-wise), but it would at the very least move FreeCAD closer to being norm conforming.
As for actual modeled threads, I do often export my models to Blender and add actual threads for rendering there, so having the option to have the exported geometry include the thread is awesome and will save me loads of work, but it's IMHO less of a priority, plus it has all the cons outlined above.
Of course, adding "fake" geometry comes with it's own issues, that I can't properly evaluate myself since I can't foresee all the unintended consequences that implementing this would have.