[OpenSCAD] Accumulating variable in openSCAD

[Philip Jones]

Hi,

I'm new here, so thanks for adding me to the list.



I would like some advice on how to achieve something in openSCAD programming
language. I want to put a row of holes into something where each hole is
larger than the last and with the holes spaced apart by the diameter of the
previous hole (basically a drill size guide).



Something like:

difference()

{

cube([90, 30, 5]);

offset = 0;

for (a = [0: 1: 20])

{

dia = 1.0+(a/10.0);

offset = 4 + (2 * dia);

translate([offset, 4, -1])

{

cylinder(h=7, d=dia);

}

}

}



This produces a row of holes of increasing size, but the increasing offset
doesn't work. I think I read that autoSCAD doesn't have "variables" like
other programming languages (clearly 'offset' isn't working how I am
expecting it to) but not being an expert (except perhaps in 'C' which I've
used for about 30 years) I don't really know what that means or how to write
something that would work.



Any advice, or code example would be gratefully received.



PhilipJ

[Mark Schafer]

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[PhilipJ]

Try two passes. First generate a list of the dia and offset as
pairs.
Then consume the list while making the objects.
dims = [ for (a=[0:20]) [1+a/10, 4+(1+a/10)*2]  ];
echo(dims);
difference() {
    cube([90, 30, 5]);
    //
    for (d = dims) {
        #translate([d[1], 4, -1])
            cylinder(h=7, d=d[0]);
    }
}

Thanks for that, I'm always learning something :-)
PhilipJ




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[PhilipJ]

Hi again,

I tried your code suggestion and it worked as it was supposed to but it made
me realize I need a more complex set of offsets. Basically the offset needs
to be:
the offset of the previous element + 2 * dia of the hole.

I'm not familiar with how to manipulate 'lists' so can you suggest how I
could do something like:

dims[i] = dims[i-1] + 2 * dia;

I only know how to show this in 'C' so it's probably nonsense in OpenSCAD
language.
I have looked through the online documentation but I can't find anything
that specifically explains this usage of creating a list or of the
for(d=dims) usage. Is this a general scripting form ? will I find it in
documentation for Python or Lua ?

Sorry for using up your time like this, I appreciate the help
PhilipJ




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[runsun]

Since Neon22 already figured out the formula to generate the offset (in the
dims), which is the critical part, there's actually no need to have 2
for-loops:

difference() {
cube([90, 30, 5]);
for (a = [0: 1: 20]) {
translate([4+(1+a/10)*2, 4, -1])
cylinder(h=7, d=1+a/10);
}
}

If the formula is too complicated to figure out (or you are too lazy), an
alternative is to use recursive module:

module holes(offset=0, d=d0, _i=0)
{
// Draw the cylinder

translate( [offset,4,-1] ) cylinder( ... );

// Draw next one with new variable values

if(_i< number_of_holes)
holes( offset= offset + ...
, d = d + ...
, _i = _i+1
);
}

In this approach you only need to worry about the relationship between the
current iteration and the one right before it.



-----

$ Runsun Pan, PhD $ libs: scadx , doctest , faces ( git ), offline doc ( git ), runscad.py ( 2 , git ), editor of choice: CudaText ( OpenSCAD lexer );&nbsp;$ Tips ;&nbsp;$ Snippets

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[PhilipJ]

Hey runsun thanks,

that worked perfectly :-)

PhilipJ




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