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How does the Frame feature choose which way to orient segments?

Corvin_BollCorvin_Boll Member Posts: 7 PRO
I created three space allocation parts using a single extrude from a singe sketch. Just three simple rectangular boxes, all constructed in the same way. If I use the Frame feature and select one edge of each, all in a line, they don't all share the same orientation (see image). How does OS choose which way to orient each segment of a frame? I would have expected these three pieces to face the same direction, given the identical way they were created. Any ideas to force them to line up correctly? I would like to use as few Frame features as possible to create my final product.
  
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Best Answer

  • Corvin_BollCorvin_Boll Member Posts: 7 PRO
    Answer ✓
    Finally figured it out: Lines have directionality. Depending on which end you started it with in your sketch. Eg, a vertical line will remember if it is "pointing" up or down. This then propagates to extruded parts. Edges remember the "direction" of the line they were created by. The frame feature takes this direction into account.

Answers

  • Corvin_BollCorvin_Boll Member Posts: 7 PRO
    Additional Info: There are other sketches, etc. present in the part studio, but I made sure the edges selected really were the edges of the intended space allocation parts. However, I created a test studio that included only the space allocation sketch and extrusion. In that test, all three beams were oriented the same way (ie, they were correct and properly aligned with one another).

    I'm still searching for an explanation as to why I'm getting different results in my original part studio. Any suggestions about things to try would be helpful.
  • Corvin_BollCorvin_Boll Member Posts: 7 PRO
    Answer ✓
    Finally figured it out: Lines have directionality. Depending on which end you started it with in your sketch. Eg, a vertical line will remember if it is "pointing" up or down. This then propagates to extruded parts. Edges remember the "direction" of the line they were created by. The frame feature takes this direction into account.
  • S1monS1mon Member Posts: 985 PRO
    I haven't used the Frame feature, but the hidden directionality doesn't surprise me. This unfortunately an issue all over. Surfaces have default normals, lines have a start and an end, sketch entities have a creation order, surfaces have a U and V direction to their paramaterization, etc. They are usually internal to the CAD system, and invisible to the user, but sometimes they get in the way. Two visually similar models with the "same" features will end up with different results because of these hidden issues.

    Onshape is deterministic, in the sense that if you go through the exact same set of steps you (should) get the same results. This is by design and critical to its ability to allow collaboration with relatively low bandwidth syncing between users. However, if two sketches which look the same are created in slightly different orders (sketching a line from left to right instead of right to left), then the downstream results can be different.
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