[OpenSCAD] Newbie question

G. Wade Johnson gwadej at anomaly.org
Wed May 22 19:21:51 EDT 2019


On Wed, 22 May 2019 22:00:23 +0200 (CEST)
Dirk Willems <dirk.willems at tutanota.com> wrote:

> Hello Guy's,
> 
> Thank you all for this wonderfull piece of software !
> 
> Just started and checking around, doing some easy test and stuff to
> learn how to work with it.
> 
> I was looking on the documentation searching on youtube but don't see
> and understand it ... So I just ask in the community if somebody can
> help me on my way. 
> 
> For starting It's kind very complex and if you know how, it will be
> very easy ...
> 
> But for now I'm struggling with the following
> 
> difference() {
>    translate([0,37,15]) rotate([90,0,0]) cylinder(h=20,r=5);
>    translate([0,37,15]) rotate([90,0,0]) cylinder(h=20,r=4);
> }
> 
> difference() {   
>     cylinder(h=30,r1=25,r2=16,central=true);
>     cylinder(h=30,r1=23,r2=14,central=true);
> }

The problem in both cases is a subtle issue that we all dealt with. The
shape you want to difference cannot be the exact same length as shape
you are subtracting from. Otherwise, you end up with a very thin
membrane at each end.

Try

difference() {
   translate([0,37,15]) rotate([90,0,0]) cylinder(h=20,r=5);
   translate([0,37,15]) rotate([90,0,0]) cylinder(h=21,r=4);
}

I normally have a constant eps, defined at the top of my file, that I
add to the lengths like this to make it obvious that I am using a fudge
factor

eps=0.01;

difference() {
   translate([0,37,15]) rotate([90,0,0]) cylinder(h=20,r=5);
   translate([0,37,15]) rotate([90,0,0]) cylinder(h=20+eps,r=4);
}

The second example works the same way with a small addition (like eps),
Doesn't work as well, adding a 1. (Wall thickness is not what you
expect in that case.)

G. Wade

> What I want to accomplish is to combine the 2 cylinders into each
> other with the inside is smooth and off course having my hole in the
> second cylinder.
> 
> Tried things like hull, intersection, union, etc ...
> Getting all of nice things but not what I want, with putting the
> intersection in it I get to opposite of what I want to accomplish, 
> 
> Very funny and having a great time with it :)
> 
> But it doesn't help me in this case 
> 
> Thank you very much for all your feedback, just take it easy on me
> please :)
> 
> Kind Regards,
> 
> Dirk 
>  
> 


-- 
It is wise to remember that you are one of those who can be fooled some
of the time.                                      -- Laurence J. Peter



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