@ianhughes7UFVF
I want to make sure you understand that you don't have to do everything exactly as I did.
You don't HAVE to make a construction line box. You could have drawn the exterior lines from one to the next using lengths and angles, for example. If you start from the origin with one line defined with a length and an angle, it will be fully defined and turn black. If you keep adding lines onto the end of the previous line, with lengths and angles, then of course they should all be fully defined and turn black also, right? I just noted by taking a few measurements in your file that the angles and lengths seemed arbitrary, and the distances from some imaginary outside corners seemed to be whole numbers (30mm mostly in this case) and so I though a construction box with corners to measure off of was useful.
You don't HAVE to use Midpoints to locate things. You can locate things in a variety of ways. You could dimension both sides and make them equal. You could dimension the whole outside box, dimension the whole inside box, and then dimension the spacing between them as = 1/2 * (outside box - inside box). It's just that using the Midpoint constraint was the quick/easy way in this case.
You don't even HAVE to use construction lines at all. You could do everything with real lines. It's just that construction lines help differentiate the design purpose, which can sometimes get pretty complex. Also they don't contribute to profiles, so using them helps reduce the number of chunks you'll have to select when you go to extrude or whatever.
Each project will be different, and each sketch idea you start out to draw might make sense in different ways. Lesson number two, if I was to make another hour long vid, would be about parameter/function usage, and specifically how it relates to drawing sketches. If you know, for example, that you're going to want that shoulder bracket to be flexible in length side-to-side, you've got to think about whether you want the diagonal braces to stretch, to move with the outside, to hold their position relative to the middle, or maybe to hold position at the bottom but stretch out to a larger angle at the top. You've got to think about that sort of stuff. There is a variety of constraint setups that lock that shape down while it's static, but if you're going to stretch out that overall 390mm length, you're going to want to set up the position of that interior angle brace in a specific way to get it to do the specific thing you want. See what I mean? You might have to set up an interior construction line and have that interior brace built off the midpoint of it, so that at the outside perimeter stretches out, so does that construction line, and so that brace built on the midpoint moves half the distance that the outside perimeter moves. Or maybe instead of using a construction line, you dimension each of the two lines defining that interior brace in such a way that they = 1/2 of the exterior dimension. Or whatever...the point is you'll want to start thinking about that kind of stuff. You'll have to picture the stretching geometry in your head and imagine how you want each bit to move or not move, and then how to dimension/constrain it to achieve that goal.
Fusion
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