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What is my student missing? This sketch will not define
kevin_olson578
Member Posts: 2 ✭
Hello! New CAD teacher here, and I'm learning Onshape alongside my students this year. We're working through the Unit 2 Skate Deck, and in 2.5, I have several students stuck trying to define their sketches when the splines are added to the sides of the board.
One student added splines, and the sketch remains defined, if he leaves the straight sides in the sketch as well, but as soon as he deletes the straight sides of the board, the whole board turns blue. See below:
I have another student who can define everything except her splines. She is working so hard to figure this out, she's spent hours digging around on reddit, etc, and when we try the suggestions she is given, usually the entire sketch turns red. Admittedly, I'm not exactly sure how she constructed the deck in the first place, but I cannot deduce what she is missing in order to define these two splines… Please help! See below:
Answers
A good tip is to try dragging a point or edge that's blue to see how things move. Then undo and constrain it so it can't do that.
If they could share the documents so we can copy and edit it would make helping much easier.
For the first one, it looks like the horizontal edges are also constraining the vertical edges to be vertical via a perpendicularity constraint. Try adding vertical constraints to both vertical lines. I bet if you dragged the end points of those lines they'll rotate about their midpoints.
For the second one, I'm not sure why her splines are not fully defined, although she does have a couple of line endpoints that aren't constrained on construction lines which will also trigger the warning.
It appears her splines should be constrained, but it's most likely one of the endpoints are not fully constrained. Perhaps she has a tiny line or something there which is the coincident constrained instead of the spline end point. One tip is though that she has daisy chained a lot of constraints. It's good practice to only dimension from a datum where feasible.
Deleting the lines most likely to have removed some constraints. Under standing constraints and how they work together is quite important.
I recommend looking into the Learning Center for videos and lessons before going o reddit and such.
https://learn.onshape.com/
https://cad.onshape.com/documents/12d9fbf125e4090eb0e04195/w/c311b64852d9200433a8f7a2/e/f508bec33e62e5da73928b41
Re: First Student - Another fix would have been to leave the two parallel lines in place, but make them construction geometry.