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How can I create a rectangular shell with concave inside edges?

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18 commentaires

  • jean luc moncel

    I'm far from being an expert, but I think once you have created the rectangle, you may draw the inside using arcs, then you draw the two surfaces, the inside surface to the thicknees of the bottom and the rim to the final height of the tray.
    Then you use the draw tool on the edges to round them.

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  • Jacant

    Use the Pull tool to create a 'Fillet' or a 'Chamfer' on the edges

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  • Tim Heeney

    Andy.

    Lets take a look...but firstly i don't really understand 'concave edges'. In the context of your sentence, i believe you're refering to something like this.

    In modeling the Addition / Subtraction / Shared Volume of touching / intersecting of solids comes under the heading of Boolean operations.

    In this case, i decided to model the inner material removal by making it a solid and removing it from the base or external solid.

    Is this what you mean by concave edges? Please confirm and i'll gladly describe the process.

    Cheers...

    EDIT: I've just seen Jacants response - it's very possible thats' totally your meaning - it is the classical DSM /Spaceclaim methodology of pulling edges etc and must be mastered. I've gone for the somewhat more complicated, Boolean 3D cad, generic technique.

    Note, neither way Shelling is being used as the interior isn't an offset from the exterior.

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  • Andy Amada

    Hi Tim,

    You hit the mark perfectly.  Yes, I would have a larger piece of wood, and from that I want to have the CNC machine carve out a tray like you show above, resulting in the gray image and the outlined one right above it.  I generally create trays with the inside sides coming down vertically and only at the bottom having the concave look, due to using a router bit for bowls, but I assume I would be able to control the slope of the sides. 

    It would be great if you could describe the process so I know which tools to use.  There is another suggestion from Jacant.  That also appears right.  Just curious - does the DSM program provide a way to capture the actual process to create a gif like what Jacant shows above or is that an external app?  I would use that feature myself.

    Looking forward to hearing from you,
    Andy

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  • Tim Heeney

    Andy - Jacant put me onto Gifcam , an external app. The current version is 6.5 i believe.

    Sadly but understandably, gif sizes are limited to 2MB per file and each is captured / created manually. Start a post and attach an image / gif by selecting the 'mountain and sun icon'.

    Jacants method is classical spaceclaim /DSM - from what Jacant has shown, it can be taken further as this shows.

    this is a very fast way to model - the initial depression may also have arcs as edges replacing the straight edges.

    I suggest you experiment with Jacants / DSM standard technique first as it's fast !

    If you want more, we can get into Booleans and also sweeping a curve along a path to make a surface / surfaces and joining them to make solids etc.

     

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  • Andy Amada

    Thank you Jean Luc - I will have to study "arcs".
    Andy

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  • Andy Amada

    Jacant - thank you very much.  I will have time later today to try out what you show.  The only process I am not sure of until I try it is creating the concave shape at the bottom.  I tried that before submitting my post, and because I chose "rounded" the curve at the bottom was convex instead of concave.  Now that I see it can be done, I will work on it.  
    Thank you,
    Andy

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  • Andy Amada

    Thanks Tim, 
    I will get Gifcam.  I will also start with Jacant's process, as you suggested.
    All the best,
    Andy

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  • Jacant

    Only get GifCam from here

    http://blog.bahraniapps.com/gifcam/ 

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  • Jacant

    The problem with using shells is that the 'solid' remembers that it is a 'shell'. So when you Pull an edge or face it keeps the Shell wall thickness. (Green solid). To overcome this Copy the shell, Delete it and Paste it. Now it has no memory of being a shell. All faces and edges can be pulled normally.

    Once you get your basic shape the inside vertical edges can be pulled or left square. the bottom fillet can be adjusted as Tim described above. All this just using the Pull tool.

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  • Andy Amada

    Jacant,
    Thanks so much for the link.  It's a great site.  A great product for such a low price.  
    Great idea on the copy and paste.  The outside edge keeps its shape when I adjust the inside shape. Very interesting and useful.
    But I do have one problem.  When I work with the shell and select the bottom edge and pull, I get a concave arch, but when I do the same with the non-shell image, I get a convex arch.  Am I doing something wrong or should I make my concave arch first then do the copy and paste?
    Appreciate your help. Thanks,
    Andy 

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  • Jacant

    But I do have one problem.  When I work with the shell and select the bottom edge and pull, I get a concave arch, but when I do the same with the non-shell image, I get a convex arch.

    Is this the inside edge you are talking about?

    First attempt with GifCam would be good here so we can see the problem.

    If it is a shell then the inside would be concave while the outside would be convex. It will always keep it's wall thickness. Do the Pull when it is not a shell. 

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  • Me Here

    Another approach to this is to define your profile and bowl shape in 2, 2D sketches, then Pull-Sweep them:

    The nice thing about this is you have full control of both profile and bowl shape independantly of each other:

    You might want to make sure there is a flat on the bottom though :)

    A couple more:

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  • Andy Amada

    Hi Jacant,

    I just downloaded and created my first gif.  I am now a very novice Movie Producer!

    Here are two links:

    Concave - this pull produces the concave curve i am looking for.
    https://www.powerpick.com/andy/dsm/concave_curve.gif 

    Convex - this pull produces a convex curve I want to avoid.
    https://www.powerpick.com/andy/dsm/convex_curve.gif 

    I don't see what is controlling which curve is produced.
    Hope you see something.
    Your input is very much appreciated.
    thanks,

    Andy

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  • Jacant

    Trick of the eye. They are both Concave. It is impossible to make a Convex curve on an inside edge using the Pull tool.

    You can attach your gifs here, use the Insert image icon.

    If you double click an edge it will select the loop so you can Pull all of the edges together.

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  • Jacant

    If you want a Convex curve on an inside edge then double click the line to get an edge loop and use the 'Cylinder' tool.

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  • Jacant

    Using the Cylinder tool on an outside edge with the 'Cut' option will give you a kind of 'Scotia bead' edge.

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  • Andy Amada

    Hello Jacant,
    I've got it now.  Thank you so much for your support, insight and helpful tips.
    I feel comfortable now with the DSM cad software and will be ordering my CNC machine in the next couple of days.
    All the best!
    Andy

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