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How to concave a flat surface?

tj_thornileytj_thorniley Member Posts: 65
edited November 2017 in Community Support
I'm trying to create a model of a microscope objective lens assembly. This is the first element in the series. It's a bit of an unusual shape, but essentially it's a cylinder with a 45° bevelled edge (the chamfer tool worked really nice, by the way). 

It's basically done, but I need to make a shallow indent/depression (concave) in the highlighted surfaces. Kind of like the inverse of a dome, hemisphere, dimple, or parabolic dish (imagine scooping it out with a spoon). If I could invert the chamfer tool (and round off the hard inside edge/corner so that it's a smooth arc/curve - like in the diagrams below) that would be perfect. 

Answers

  • NeilCookeNeilCooke Moderator, Onshape Employees Posts: 5,310
    Please take a look at the revolve feature. You could do that part all in one sketch/revolve. 
    Senior Director, Technical Services, EMEAI
  • tj_thornileytj_thorniley Member Posts: 65
    Okay, sweet. I've been trying with the revolve tool tool but can't seem to get it to co-operate. Would you mind going into more detail? What's the correct procedure? I just need to push it in about a millimetre or two at the deepest point. Thanks in advance, much appreciated.
  • NeilCookeNeilCooke Moderator, Onshape Employees Posts: 5,310
    You need to draw only half a section something like this (badly drawn, I know):


    Senior Director, Technical Services, EMEAI
  • tj_thornileytj_thorniley Member Posts: 65
    So, it's kind of like using the symmetry tool, but you end up with a 3D cylindrical / spherical object? Surely there's a way to modify the solid I already have? I suppose I could try to split the current model in half and use the 3-point arc tool (and trim) to carve out the concave.

    But for more complicated models that's going to be a major hassle. Rather than drawing the whole thing in a single sketch, I usually start with a basic sketch of a single shape, extrude, then sketch from a surface of the new solid, then extrude, and so on.
  • john_mcclaryjohn_mcclary Member, Developers Posts: 3,890 PRO
    Revolve is the best way for this shape.

    But if you really like to trim away at a solid you can use boolean operations and making your cuts that way
  • owen_sparksowen_sparks Member, Developers Posts: 2,660 PRO
    edited November 2017
    Yes as the chaps mentioned
    Option 1 Revolve remove the bits you want to cut away from your existing part.
    Option 2 New Revolve to create whole part in one go. Note:- Easier than option 1 :wink:

    You can even use the equations you've posted above to drive the sketch for the revolve if you wish.

    Owen S.
    Business Systems and Configuration Controller
    HWM-Water Ltd
  • tj_thornileytj_thorniley Member Posts: 65
    edited November 2017
    Here, I got it to work using revolve, from scratch.


    Then bevelled the edge with the chamfer tool.



    Changed the material to glass, edited the appearance to a translucent blue, and hid the intersecting planes.


    But I still haven't managed to scoop the concave out of an existing object. This shape is relatively simple, but I anticipate having to do this kind of operation on more complex solids in the future. Having to redraw a completed part from scratch every time I want to make a minor adjustment is very quickly going to become a major headache. Especially if the dimensions are already specified. 

    I've tried to be detailed and include diagrams depicting every step of the procedure (not unlike a tutorial). If someone could do the same for me, I would really appreciate it. Thanks in advance.
  • owen_sparksowen_sparks Member, Developers Posts: 2,660 PRO
    edited November 2017
    Howdy.

    Removing from an existing part is exactly the same but instead of selecting the "new" option on the revolve you select "remove" and then which part you want to remove it from. Termed the merge scope, shown below.



    The highlighted area is the new sketch used to make the cut away.  (The actual grey part was created earlier from an extrude of a circle.)

    Note shown with cross section turned on as it shows the concave nature better, the part is of course whole with that view turned off.



    File here:-
    https://cad.onshape.com/documents/b6a887c3cdcfbf681b9c9373/w/f16831af92b9443420026b87/e/2b158c9b00f1666108d2bff7

    Owen S


    Business Systems and Configuration Controller
    HWM-Water Ltd
  • john_mcclaryjohn_mcclary Member, Developers Posts: 3,890 PRO
    edited November 2017
  • owen_sparksowen_sparks Member, Developers Posts: 2,660 PRO
    edited November 2017
    Too slow, chicken marango o:)

    Owen S.
    Business Systems and Configuration Controller
    HWM-Water Ltd
  • john_mcclaryjohn_mcclary Member, Developers Posts: 3,890 PRO
     :'( 
  • owen_sparksowen_sparks Member, Developers Posts: 2,660 PRO
    Have an up-vote anyway :p
    Business Systems and Configuration Controller
    HWM-Water Ltd
  • tj_thornileytj_thorniley Member Posts: 65
    Thanks for the quick replies fellas. I did try something like that, but to no avail. I'll try it again in a bit, with your examples to guide me. Hopefully this helps someone else too. By the way, how did you do the cross section view? That could be useful.
  • john_mcclaryjohn_mcclary Member, Developers Posts: 3,890 PRO
    There is a lot of neat things you can do with section view, but this is the basic start:

    For more info you should check out the OnShape youtube channel. All kinds of stuff to look at there, including a complete run down of this

  • ollie_morrisonollie_morrison Member Posts: 5
    How do you do this with a shape that is not spherical? I have a softly rounded triangular shape that i need to add a concave into. 
  • Jake_RosenfeldJake_Rosenfeld Moderator, Onshape Employees, Developers Posts: 1,646
    @ollie_morrison

    It will be easier to help out if you post a link to your document (see instructions here https://forum.onshape.com/discussion/9107/forum-post-checklist-read-this-first#latest)

    and some additional context on what you have now and what you would like to achieve.  
    Jake Rosenfeld - Modeling Team
  • john_mcclaryjohn_mcclary Member, Developers Posts: 3,890 PRO
    @ollie_morrison
    All you need to get a section started is at least 1 flat surface or plane.
    Once you have a flat surface selected, you can move/rotate the manipulator wherever you need.

    If you grab the circle at the base of the arrow, then you change the start point of the section and you can snap it to any other vertex, including the origin.


  • jeremy_irwinjeremy_irwin Member Posts: 4
    This is great! Thanks for the tip. Can you help me make a concave indent on the top of a square object?
  • glen_dewsburyglen_dewsbury Member Posts: 559 ✭✭✭
    Just because I was too slow and everybody agrees revolve is best. Here's a loft version. LOL
    https://cad.onshape.com/documents/d2a86f2a038bac6976d055a0/w/aafeaeea2f5793f490b24e03/e/a11571ff46247090ae374903
  • john_mcclaryjohn_mcclary Member, Developers Posts: 3,890 PRO
    I'm not sure how to make a concave square without having sharp edges.

    I tried lofting and ended up with more creases that just extruding circles then boolean subracting.

    I'm imagining a soap bubble shape is more what you're looking for right?
    Which is a bit out of my wheelhouse

    https://cad.onshape.com/documents/7049d342b4e7ee052d899f27/w/3de4a12eb3cc3680b0e6edf9/e/09a515e631373149c6cfca54


  • S1monS1mon Member Posts: 2,321 PRO
    Fill surface is good for adding some crown to a surface. As @john_mcclary says, it's hard to avoid getting some sort of crease or convexity in the corner unless you cheat things a little.

    This document has a relatively quick and dirty way to do it:



  • wayne_sauderwayne_sauder Member, csevp Posts: 472 PRO
    You can also create a sphere and boolean subtract away. 
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