FreeCAD Quick Tips - A simple method to avoid topology issues when using datum planes.

[Music] so i just wanted to run through this topology issue i've seen a number of videos now that are showing how to get around the topology thing in freecad so let me just start up a new sketch and we're just going to sketch something quick and simple so we're going to go with a square rectangle pop it on there we're gonna just quickly um constrain the sketch i'm just gonna do symmetry is what i'm going to do so i'm going to do this guy and this guy with that one symmetry that's done a couple of dimensions and we should be golden so we're going to make that and that are dimensions and doesn't really matter that what the actual dimensions are so i'm going to close that and i'm going to pad that guy so we'll just go here hit that pad i'm going to just make that three male pad now what i want to do is from my pad let me just pop into the middle from my pad there's my three mil pad i want to be able to cut in a shape in the bottom here so what i'm going to do is i'm going to add and we're going to switch on our planes for that pad i'm going to select that one and create a reference plane so now my reference plane is on there it's to the x y plane and i'm going to offset it in the z direction the same amount that i made that pad so you'll see we are now offset in that plane so i'm gonna say okay to that turn off those origins just so it's a little cleaner and now you can see i'm actually drawing on the same place as that thickness well of course if i do that and that thickness changes now my plane is going to be in the wrong spot so here's what we do we go to a spreadsheet and we'll tile those windows we'll create a new spreadsheet and i'll tile those windows and then i'm going to say uh pad thickness so we'll just call it pad thickness for now you call it whatever you want remember this column is just so i can remember what i am calling it i'm going to make it three at the moment i'm gonna go here and i'm gonna give it an alias of pad t so that is now variable i'll go back to my pad and i go to my it's actually called length in the pad i'm going to pop that up and now i'm going to make that spreadsheet dot pad t so now you can see it's still three mil because that's what that is but that now makes this a variable so guess what we're going to do next we're going to take this date and plane and we're going to look for that date and planes offset so we go back into the date and plane go in here and we make this spreadsheet and pad t simple now that date and plane is always going to be where that thickness is and equally if i wanted it to be in the center of that i could just say pad t divided by two if i wanted to be one third of that you know we we can do the math right so we can put it anywhere we want i'm using the same variable to drive that thickness as i am to drive that plane so if i do if i make this number five you see everything moved at the same time so given that we've got one spreadsheet with one variable and now what we're going to do is we're going to create a sketch so we'll go back into our part design and we're going to make our sketch actually on this plane so we're going to sketch and we're now sketching on this plane and we can cut out whatever we want to cut out let's cut out a slot that starts here and runs up to here and i'm not going to constrain this just just for demonstration purposes so close that we make pocket and that pocket now can go through the whole thing and we say okay and then of course we want to check and see if that's going to be good when we modify the original sketch so let's go back into the original sketch and let's just center that and what we're going to do is we're going to create a couple of lines here just to show that we're creating new faces so i'm gonna just cut that guy there and then i'm gonna select this and this and i'm gonna mirror that and then i'm gonna cut off this and this and now one thing you do have to check is when you do all this kind of stuff is that these things are all connected to each other so you can see that one is not you know catch out every time when you go to look at your pad your pad will be broken and it'll be because your sketch lines are broken and whenever you modify the sketch you can break some of the um constraints particularly if you have this auto remove redundance and auto update so you know you gotta be a little bit careful of that so i'm gonna close that and see if my guy is still there yep everything looks perfect and if i pop into that so you can see it you can see i changed the faces and of course that changed now if i want that pocket only to go halfway through there just to give you a quick idea of how you do that we're going to go in here this was spreadsheet pad t just divide it by two and now if i say okay there may be some recompute stuff to do so i'm going to recompute that guy because you can see that little check mark that comes up on it so it wants you to recompute everything to make sure we're on our latest and greatest and now that slot goes halfway through because it's that thickness divided by two so what happens if i change that thickness well if we go back to our pad and we can see our pad is five mil from the spreadsheet so i'll go back to the spreadsheet and let's just move that guy over there go back to our spreadsheet now i make this eight mil and you can see perfectly that this thing is halfway it's always going to be halfway through the middle and there it is cutting this guy off now obviously if i if i move this edge up here above that slot it's not going to change but we could constrain that in a way to keep that in the same place too so this is just a quick video just to show you how to do that and how that works and how that gets over the topology issue obviously the topology issue is if i had to draw on this slot on this face and then i created these extra faces it would blow this thing up and so again another it's just a quick tip but i just wanted to do this quickly because i had no some people were having some issues with it and if you like this just uh like this video and subscribe to the channel i'd appreciate it thanks you

Channel: Adventures in creation

Views: 14,388

Keywords: CAD, CAM, DIY, FreeCAD, MPCNC, HobbyCNC

Id: e0pvw1weSuM

Length: 8min 19sec (499 seconds)

Published: Tue Oct 20 2020

Reddit Comments

[u/rev667]

Useful vids :)

[u/vivivitus]

Thanks for the hint. I'm new to freecad and this always bothered me. Do you know, why the program is not adding new face ids after the existing ones?