Hi c/FreeCAD, totally newbie here! I’m having a ton of fun learning FreeCAD, but I have a small question. I know the toponaming problem is going away soon, and maybe that makes this kind of irrelevant, but I’d still like to know.
Sometimes when I’m watching or reading guides on avoiding the toponaming problem, the person will say something along the lines of: “actually this technique is also more professional/proper/correct anyway, real engineers do it this way.” Basically that the methods that avoid the problem are also just best practices in general. But they always say that as kind of an aside, and I wish they’d say more! What makes those methods better? Does anyone have any suggestions for articles or videos about this?
For one example, there was one guide that suggested you should use a datum plane instead of referencing one of the object’s surfaces. I understand the toponaming problem well enough to get why referencing a surface can cause it. However, the person in the guide used the same surface that would have been referenced, as the attachment point for the datum plane. Why does that not produce the same issue?
Disclaimer, I’m at a sortof “advanced hobbyist” level of cad. My understanding of the topological naming problem in general is that it exists in all cad because it is a sortof byproduct of how computers keep track of data about 3 dimensional objects. If you make a cube, all the sides need to have an identifier associated with them. If you put a hole in that cube, you now have more identifiers and have to decide what ordering makes sense. It sounds easy to work around with a cube but when models get really complex it’s not so easy, especially when you change something way back at the beginning which creates more or less faces in the middle of the list somewhere.
Freecad isn’t making the topological naming problem “go away”. They are creating (or rather merging, it’s been around a long time) an algorithm that makes a better guess at what the order should be, rather than sticking new faces in the list and reordering without any consideration of what happened after that face was created. This is, as far as I understand, also how other CAD packages do it, and you can still back yourself into a topological naming problem if you try hard enough (or don’t try at all I guess) in both freecad with the new changes applied, and in other CAD packages.
So “best practice” is to be smart about the attachment of your geometry thinking about how things might change in the future, rather than clicking the closest face whenever you need a sketch plane. In reality modern proprietary cad is so good at guessing and maintaining consistency that it doesn’t matter unless your model is horrendously complex and whoever made it didn’t pay any attention to laying out the base sketches in an organized way.
For example if you make a flange but you’re not quite sure about the thickness, base the sketch for say, the holes, on the parallel origin and offset it by the height of the pad or the length of the sketched geometry. Or use a spreadsheet or variableset for the value of both the thing that you define the thickness with, and the offset from the origin plane. That way if the value changes, nothing will break.
I made a test model but it isn’t something that shows up well in a single screenshot unfortunately. See the “Flange Thickness” and z offset parameters in the property view. I used that for the flange dimensions, and the hole sketch offset.