[OpenSCAD] Making a whole of small parts

adrianv avm4 at cornell.edu
Sat Jul 27 18:08:49 EDT 2019

The referenced message suggests creating parts with standardized locations. 
This is not unreasonable, but I think it is inflexible and messy, in the
end.  (If you want to place the part on something, how do you do it?  You
have to know the part dimensions.)  In BOSL2 the author has been working on
giving parts a set of "anchors", and I think this is a great idea.  You can
have standard anchors such as the left side and right side or top and bottom
of a part, but you can also add special anchors for screw holes or other
special locations on each part.  Then you can have your modules place the
specified anchor point at the origin.  This is much better than having to
move parts around based on knowing that they start with their centers at the
origin or something like that.  I find it always seems a remarkable struggle
to get a part that appears in the first quadrant, for example, rotated and
positioned correctly.  

I think also the Relativity library does something similar, and the obiscad
attachment library was also an inspiration for this approach.  

With regards to creating a part, you should use whichever is easier of
mirror or translate, or makes the construction easier to understand.  Once
the geometry has been created, it won't make a difference which commands you
used to create it.  I did run into a gotcha with mirror---my part had
chirality (screw threads) and mirror changed its handedness. 

gounthar wrote
> Sorry for not being clear at all. 
> Discuss
> <http://forum.openscad.org/Making-a-whole-of-small-parts-tp27057p27058.html>  
> got it right despite my bad explanations.
> I have several problems. For "big"  boxes
> <https://github.com/gounthar/MerryKombo/blob/CAD/big.png>  , I have
> small 
> sections
> <https://github.com/gounthar/MerryKombo/blob/CAD/usb2uart.png>  
> (which are not parts but a part of the box) which have lots of symmetry.
> My first problem/question was: what is the correct way to code that
> symmetry? Should I use mirror, or translate?
> I guess I should use mirror, and that leads to the second question: does
> it
> change anything to use mirror or translate, knowing that this section will
> be inserted in the final part, and maybe in other parts later on? It
> should
> be "agnostic", like a component in classic development, but easily
> inserted
> wherever its final position in the part may be.
> Another example would be the  camera hole
> <https://github.com/gounthar/MerryKombo/blob/CAD/camera_view.png>  
> for the
> same  part
> <https://github.com/gounthar/MerryKombo/blob/CAD/big%20with%20camera%20view.png>  
> The problem I have with onShape regarding this sections is that I don't
> know
> how to cut them in order to only print them to see if they fit, and not
> the
> whole big part with them included. I guess I could do that with parts
> studios and parts assembly, but I already have way too many tabs for that
> project. That's why I was pretty happy to find OpenSCAD with modules so
> that
> I can refine those small sections before integrating them into the big
> part.
> Yes, I'm measuring more than twice before printing, but there are still
> some
> errors or improvements after the first print (especially with OpenSCAD, as
> I'm used to rely on the tool just by using constraints to get things
> right,
> in comparison with OpenSCAD where I have to work out the right numbers by
> myself).
> I hope I did not muddy the water more than in my previous message...
> Thanks.
> --
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