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What is the proper way to model this?

øyvind_kaurstadøyvind_kaurstad Member Posts: 234 ✭✭✭
Look at this very basic model:



It is just a circular base shape, and it has two protruding arms. The arms are pointing upwards, and they are also pointing outwards from each other.
Assume that I want the top surfaces of these arms to be parallell, so that a plane surface would rest flat on both arms.

What is the best way to model something like this? The model shown here isn't correct, it just shows the basic shape I'm after. The easiest method I could find, was actually to create a plane just above the arms, and then use replace face to make the top surface of the arms parallell, but somehow that feels like cheating. I could of course create that plane first, and then sketch on it and extrude down, but that would make the attaching point to the base look slightly funny. I should add that in this example I only modeled one of the arms, and then mirrored it.

This is probably a painfully basic question for you experienced modellers out there, but for a novice it isn't immediately obvious how to best do this.

Best Answer

Answers

  • michał_1michał_1 Member, Developers Posts: 214 ✭✭✭
    edited January 2016
    simplest? two rectangles, one tilted (arm), crossing the base one (with rectangle as half of cylinder). Then, one revolution and one extrusion (symmetric), to get other arms, use circular pattern (pick faces). Done.


  • matthew_menardmatthew_menard Member Posts: 96 ✭✭
    Here's my quick and dirty attempt.  I used the front plane for the arm sketch, so if you look at it top down, the first arm is horizontal and the second is rotated up per the value in the circular face pattern.  Two sketches, three features keeps it pretty bare bones.  Although it could probably be made more robust with some equations instead of my hacky construction lines that keep the arm extrude inside the base circle extrude.

    https://cad.onshape.com/documents/4d3a3befc86f475c86e135ad/w/ea2bd8a23ebc4bdcbf2079cf/e/ef012749ae6d47fca116b6b6

  • michał_1michał_1 Member, Developers Posts: 214 ✭✭✭
  • _Ðave__Ðave_ Member, Developers Posts: 712 ✭✭✭✭
    Hmm, I thought the op requested that the top faces of the arms be co-planer to each other?
  • michał_1michał_1 Member, Developers Posts: 214 ✭✭✭
    ok, now I got that
  • matthew_menardmatthew_menard Member Posts: 96 ✭✭
    Nice! I definitely like that approach better.  I still have a bit of unfounded fear of combining my sketch geometry for all of my features in one sketch.  I know it's not a problem, especially in OnShape, but I'm still working out the apprehension to having multiple closed loops in a sketch.  However, I guess it could be argued that one's individual use case may drive you to have multiple sketches and that there isn't one single correct way to get to the final product. 
  • øyvind_kaurstadøyvind_kaurstad Member Posts: 234 ✭✭✭
    Thanks for taking the time, guys. However, _Dave_ is the only one that provided a valid solution, with coplanar top faces of the arms. Basically his solution is one of the solutions I outlined in the OP. The issue with it is that where the arms attach to the circular base it looks a bit funny due to how the geometry intersects. It looks better if the vertical lines of the intersection are close to vertical, which they are not with that solution.

    However, to acheive this, some geometry has to look weird, so to speak. If the intersection between the circular part and the arms looks good, and the top faces are coplanar, then the end faces of the arms will not be rectangular.


  • øyvind_kaurstadøyvind_kaurstad Member Posts: 234 ✭✭✭
    Ok, I've accepted _Dave_'s answer, as it is technically satisfies my question.
  • _Ðave__Ðave_ Member, Developers Posts: 712 ✭✭✭✭
    øyvind_kaurstad Sorry, don't have a solution for keeping the edges vertical and the end rectangle. But it looks better with a fillet where it joins at the base.   :)  
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