Challenge: Create an Impossible to Make Object in CAD

[Nicholas Farr]

On Nicholas Farr Said:

Hi Dave, I don’t agree that the colour scheme (which I added) fools the eye. The hand drawn pencil drawing was just lines without any shading on a plain sheet of white paper, and represented four straight planks of wood, and had the same affect as my coloured example, so to convince me, you will have to make one out of four pieces of wood, or metal if you like, which are joined together as shown.

Regards Nick.

Ah but the lines don’t represent four straight planks of wood, they’re an optical illusion.   It only works on paper because no dimensions are provided.

To convince me you have to draw the object in three elevations: plan, side and end (or plan, side and front).    I think you’ll find that it’s impossible to maintain the illusion if technical drawing requirements are met.

As I showed the object is nearly legal provided all the Z dimensions (depth) are equal, meaning it’s flat, and can be cut from a sheet of paper.  It becomes unreal only if the lines represent depth, and they don’t.

This one is an example of an object that can’t be manufactured because it doesn’t have a valid 3D geometry.   It’s a 2D representation that looks as if it might be a valid isometric projection of a 3D object, but isn’t.

I’m after an object drawn in CAD that is valid in three dimensions, AND cannot be manufactured.   Been a few interesting suggestions but so far it appears that if an object can be drawn within the rules of geometry, it can be manufactured.   The risk seems to be excessive cost, or that the part is impossible to assemble or maintain when combined in a structure.  Not that it’s impossible to make in the first place.

Dave

 

[Nigel Graham 2]

On Nigel Graham 2 Said:

That arrangement may be impossible to model in 3D CAD, and certainly would be in real wood, but would Paint and similar work in a very different way because they process only 2D images?

Anyone ever played with Pov-Ray? In computing terms it is an artistic version of CAD by making 3D-impression images, but is purely for pretty pictures not serious design tasks. That could well give you images impossible, or at least very hard, to model physically. I don’t know its current form but the version I have is entirely command-line driven, though surprisingly not ever so difficult to use, at least at a basic level.

 

 

POV-Ray is a renderer for 3D scenes which however fantastical, have to be geometrically consistent, so it can’t render anything impossible.

People often think that 3D computer animation is ‘easier’ than traditional hand drawn cell animation, but this isn’t necessarily the case. Since 3D characters have to be modelled to be consistent from all angles like a sculpture, you can’t cheat the way you can if you’re drawing. If you step frame-by-frame through a very dynamic cell animation, like the ones produced by Warner Bros. (Bugs Bunny, Sylvester, Road Runner, etc.), you’ll find frames where the character sprouts multiple arms or eyes as they engage in fast (and, preferably, violent) action. At 12 or 24 frames per second you don’t see it, but it makes for a much more punchy effect.

[duncan webster 1Participant @duncanwebster1]

The Penrose tribar show by Paul L can actually be made in real life, but it only works if viewed from one direction, see https://en.m.wikipedia.org/wiki/Penrose_triangle

[Anonymous]

Sphere (solid or hollow) within a hollow sphere (no supporting members) would satisfy the conditions wouldn’t it?

[JasonBModerator @jasonb]

No as you could metal print it, some of the metal printing methods do not need support. The similar item that Howard suggested in the first reply to this post with the ground internal surface would be more difficult though

[Speedy Builder5Participant @speedybuilder5]

How about a hollow contiguous metal cube filled with oil and no air ? I have always wanted one of those !!

[Paul LousickParticipant @paullousick59116]

How about one of these

 

[duncan webster 1Participant @duncanwebster1]

<p style=”text-align: left;”>Very nice, let’s have some pictures from different directions</p>

[NealebParticipant @nealeb]

That isn’t a bit of Photoshop artefact I see in the top RH corner, is it? The IT equivalent of an angle grinder to tidy up things that aren’t quite right cosmetically…

I made something similar on my 3D printer which was quite convincing, especially the image with a pen through the centre to “prove” it was real. Took a while to get the angle and distance right to get an effective image, though. Baffled my French class when I gave a little talk on it. About as much as looking for a good translation of “the camera never lies” did me!

[Nigel Graham 2Participant @nigelgraham2]

I don’t know if others find this, but Paul’s fabricated frame had a very peculiar optical effect of alternating rapidly from the left-hand and rear members being on the ground and at the top.

Looking at it steadily again, it seemed to settle with the LH member apparently on the floor and the middle member meeting the top of the column!

I have seen a similar switching effect with other optical illusions, especially M.C. Escher’s interior scenes in which we can’t decide if we are looking at the underside of the stairs, or down on them; but in those the effect is quite slow and almost deliberate.

This time though the effect was fluctuating very rapidly, and can only guess as a result of my brain trying to make sense of what looks like a genuinely welded steel frame standing on a concrete floor, rather than a two-dimensional image on a neutral background.

Having typed that with the image off the top of the screen I looked back at it, and the effect returned but less definitely.

[Nealeb]

On Nealeb Said:

[…] About as much as looking for a good translation of “the camera never lies” did me!

Have you tried DeepL ?

… this translation looks, and sounds, pretty good to me:

https://www.deepl.com/en/translator#en/fr/the%20camera%20never%20lies

MichaelG.

[Author]

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