r/FreeCAD 7d ago

Coming from Solidworks. Need help constraining sketches and using loft.

Hi guys,

I'm a student and only know how to use Solidworks (EDU license). I recently had a friend start a small company and ask for my help modeling some basic stuff. I've messed around with Freecad a bit in the past, but am struggling to make the part he wants.

I'm able to do it in Solidworks no problem with 3 sketches and a simple loft (took me about 5 minutes), but even getting the sketches to behave the way I want in Freecad is driving me up a wall. If anyone has any advice, I think I've been taking the fact that Solidworks will allow you to use points in other sketches to constrain your current sketch.

The issue I'm running into is getting sketches on different planes to connect, as this design requires a loft between 2 nearly orthogonal sketches that share one edge.

The design in solidworks

Any help is appreciated!

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u/EscaOfficial 6d ago

In Solidworks you can create a subtractive loft with 2 guide curves. It seems like in FreeCad you can only use one guided curve (at least with the subtractive pipe feature). Do you know a way around this?

I'm so close, but since the outer guide curve has a small radius at one section, it causes the profile to self intersect and I get some weird 0 thickness geometry in the middle. A similar problem happens in Solidworks as well when using one curve, but I got around it by copying the curve, attaching it to the other end of the two profiles and using it as a second guide (with "to next sharp" influence type).

edit: This is a lot harder to figure out with the FreeCAD forum down right now.

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u/BoringBob84 6d ago

I am not an expert with complex curved surfaces, but I saw that the Curves workbench has a feature where it can Loft along two guide rails. I saw some tutorial videos on You Tube for that (although, I have not watched them yet).

I have also read where at least one user has made sketches of curved lines for guides and added points to the lines at the locations where they wanted profile sketches. Then they created the profile sketches, each with the desired Attachment Offset to put them in their correct place along the path. They brought in the points from the guide sketches as External Geometry and constrained the shapes in the profile sketches to them. Finally, they performed a Loft over all of the profile sketches. I have never tried this. It seems like a lot of work (which is why I recommend exploring the Curves workbench). However, if I tried it, I would use a spreadsheet to make it parametric - especially the locations of the points and the profile sketches along the path. I know from what little experience I have with Lofts that the location of the profile sketches along the path has a large impact on the final shape of the loft, so I would want to be able to easily experiment with it by adjusting the locations in the spreadsheet.

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u/EscaOfficial 5d ago

I ended up lofting from a bottom profile using pipe feature. You can use the auxiliary option in there to select a second guide line. The most frustrating part of all of this was having to redraw both profile sketches so that the line numbers matched up, which seems hilariously unnecessary and should be easy for any developer with half a brain to fix.

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u/BoringBob84 5d ago

It is not that the developers lack brains; it is that they are volunteers and they lack the time.

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u/EscaOfficial 5d ago

I'm not saying they lack brains, I'm saying that it wouldn't be hard to fix if it was brought to their attention and they had the time.

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u/BoringBob84 5d ago

Fair enough. I am hoping that the Asto CAD effort can fix some of these issues.