Getting hull() to work difference()? (Subtracting variable-depth spiral from a cube)
I have the following program, that is meant to construct a spiral that gets
progressively deeper, by using hulls between successive extrusions of the
circles that make it up. (A circle is extruded, then hulled to the next
one, etc). This is then subtracted from a cube.
If I uncomment the plotSpiral() command at the bottom (without the
difference), it renders as I expect. But with the difference, it
differences the extrusions, but not the hulls between them. So the inside
of the spiral, where the individual extrusions overlap, it works like I
want (sort of), but on the outside, I just get a series of individual
pockets.
I could change the angle spacing as I get further out (that would look
cleaner too), but that would take longer, and this whole thing will be done
with a ball-nose end mill anyway, which should smooth it out on it's own.
Does anyone have any other ideas of how to get a "deepening spiral" design?
Thanks,
JIm
module plotSpiral(spiralWidth, spiralHeight = 0, spiralThickness = 1,
snakeSides = 5) {
// Number of sides of the "snake"
$fn = snakeSides;
bumpiness = 1;
segmentsPerTurn = 35;
numTurns = 4;
numTurnsToPlot = 4;
// *** Derived ***
jCeiling = 1/numTurns*numTurnsToPlot;
sphereDiameterOne = spiralThickness/bumpiness;
sphereDiameterTwo = spiralThickness/bumpiness;
//spiralWidth = 30;
//spiralHeight = 100;
spiralNumSegments = segmentsPerTurn * numTurns;
spiralRadius = spiralWidth/2;
exponent = 1.685;
//ORIG: exponent = 1.685;
function L_Spiral (angle,
radius = 50, spiralDepth, turns = 4,
exponent = 0.685, start_angle = 0) =
let (fx = exponent < 0 ?
pow( max(0, 1-angle), 1/abs(min(-1, exponent-1) )) :
pow( max(0, 1-angle), max(1, exponent+1) ),
depthVar = (angle * spiralDepth)
)
[(radius * fx ) * cos(start_angle +
angleturns360sign(turns)),
(radius * fx ) * sin(start_angle +
angleturns360sign(turns)),
depthVar];
for (angle = [0 : 1/spiralNumSegments : jCeiling]) {
hull() {
//echo(angle);
translate(L_Spiral (angle,
spiralRadius, -spiralHeight, numTurns,
exponent, 0 ))
linear_extrude(angle * spiralHeight)
circle(d = sphereDiameterOne);
translate(L_Spiral (angle + 1/spiralNumSegments,
spiralRadius, -spiralHeight, numTurns,
exponent, 0 ))
linear_extrude(angle * spiralHeight)
circle(d = sphereDiameterTwo);
} // hull()
} // for j
} // plotSpiral()
spiralWidth = 30;
spiralDepth = 5;
///*
difference() {
// Subtract the spiral from the cube
translate([-spiralWidth/2, -spiralWidth/2, 0])
color("red", 0.3)
cube([spiralWidth, spiralWidth, spiralDepth*2]);
translate([0, 0, spiralDepth*2 ])
plotSpiral(spiralWidth, spiralDepth*3, snakeSides=5);
} // difference
//*/
//translate([0, 0, spiralDepth2 ])
// plotSpiral(spiralWidth, spiralDepth3, snakeSides=5);
sitting here with the mobile on the bus, but
linear_extrude(angle * spiralHeight)
circle(d = sphereDiameterOne);
why not just cylinder(h=angle*spiralHeight, d=sphereDiameterOne)
Msquare
fre. 17. dec. 2021 20.41 skrev Jim Witte jim.witte@gmail.com:
I have the following program, that is meant to construct a spiral that
gets progressively deeper, by using hulls between successive extrusions of
the circles that make it up. (A circle is extruded, then hulled to the
next one, etc). This is then subtracted from a cube.
If I uncomment the plotSpiral() command at the bottom (without the
difference), it renders as I expect. But with the difference, it
differences the extrusions, but not the hulls between them. So the inside
of the spiral, where the individual extrusions overlap, it works like I
want (sort of), but on the outside, I just get a series of individual
pockets.
I could change the angle spacing as I get further out (that would look
cleaner too), but that would take longer, and this whole thing will be done
with a ball-nose end mill anyway, which should smooth it out on it's own.
Does anyone have any other ideas of how to get a "deepening spiral" design?
Thanks,
JIm
module plotSpiral(spiralWidth, spiralHeight = 0, spiralThickness = 1,
snakeSides = 5) {
// Number of sides of the "snake"
$fn = snakeSides;
bumpiness = 1;
segmentsPerTurn = 35;
numTurns = 4;
numTurnsToPlot = 4;
// *** Derived ***
jCeiling = 1/numTurns*numTurnsToPlot;
sphereDiameterOne = spiralThickness/bumpiness;
sphereDiameterTwo = spiralThickness/bumpiness;
//spiralWidth = 30;
//spiralHeight = 100;
spiralNumSegments = segmentsPerTurn * numTurns;
spiralRadius = spiralWidth/2;
exponent = 1.685;
//ORIG: exponent = 1.685;
function L_Spiral (angle,
radius = 50, spiralDepth, turns = 4,
exponent = 0.685, start_angle = 0) =
let (fx = exponent < 0 ?
pow( max(0, 1-angle), 1/abs(min(-1, exponent-1) )) :
pow( max(0, 1-angle), max(1, exponent+1) ),
depthVar = (angle * spiralDepth)
)
[(radius * fx ) * cos(start_angle +
angleturns360sign(turns)),
(radius * fx ) * sin(start_angle +
angleturns360sign(turns)),
depthVar];
for (angle = [0 : 1/spiralNumSegments : jCeiling]) {
hull() {
//echo(angle);
translate(L_Spiral (angle,
spiralRadius, -spiralHeight, numTurns,
exponent, 0 ))
linear_extrude(angle * spiralHeight)
circle(d = sphereDiameterOne);
translate(L_Spiral (angle + 1/spiralNumSegments,
spiralRadius, -spiralHeight, numTurns,
exponent, 0 ))
linear_extrude(angle * spiralHeight)
circle(d = sphereDiameterTwo);
} // hull()
} // for j
} // plotSpiral()
spiralWidth = 30;
spiralDepth = 5;
///*
difference() {
// Subtract the spiral from the cube
translate([-spiralWidth/2, -spiralWidth/2, 0])
color("red", 0.3)
cube([spiralWidth, spiralWidth, spiralDepth*2]);
translate([0, 0, spiralDepth*2 ])
plotSpiral(spiralWidth, spiralDepth*3, snakeSides=5);
} // difference
//*/
//translate([0, 0, spiralDepth2 ])
// plotSpiral(spiralWidth, spiralDepth3, snakeSides=5);
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Well, I moved the spiral a bit higher, changing the bit inside the
difference to:
translate([0, 0, spiralDepth*2+0.1])
plotSpiral(spiralWidth, spiralDepth*3, snakeSides=5);
And it worked. Before I guess it just didn't quite go through the top of
the cube, and I guess that screws up the hull for some reason.
On Fri, Dec 17, 2021 at 2:49 PM Michael Möller private2michael@gmail.com
wrote:
sitting here with the mobile on the bus, but
linear_extrude(angle * spiralHeight)
circle(d = sphereDiameterOne);
why not just cylinder(h=angle*spiralHeight, d=sphereDiameterOne)
Msquare
fre. 17. dec. 2021 20.41 skrev Jim Witte jim.witte@gmail.com:
I have the following program, that is meant to construct a spiral that
gets progressively deeper, by using hulls between successive extrusions of
the circles that make it up. (A circle is extruded, then hulled to the
next one, etc). This is then subtracted from a cube.
If I uncomment the plotSpiral() command at the bottom (without the
difference), it renders as I expect. But with the difference, it
differences the extrusions, but not the hulls between them. So the inside
of the spiral, where the individual extrusions overlap, it works like I
want (sort of), but on the outside, I just get a series of individual
pockets.
I could change the angle spacing as I get further out (that would look
cleaner too), but that would take longer, and this whole thing will be done
with a ball-nose end mill anyway, which should smooth it out on it's own.
Does anyone have any other ideas of how to get a "deepening spiral"
design?
Thanks,
JIm
module plotSpiral(spiralWidth, spiralHeight = 0, spiralThickness = 1,
snakeSides = 5) {
// Number of sides of the "snake"
$fn = snakeSides;
bumpiness = 1;
segmentsPerTurn = 35;
numTurns = 4;
numTurnsToPlot = 4;
// *** Derived ***
jCeiling = 1/numTurns*numTurnsToPlot;
sphereDiameterOne = spiralThickness/bumpiness;
sphereDiameterTwo = spiralThickness/bumpiness;
//spiralWidth = 30;
//spiralHeight = 100;
spiralNumSegments = segmentsPerTurn * numTurns;
spiralRadius = spiralWidth/2;
exponent = 1.685;
//ORIG: exponent = 1.685;
function L_Spiral (angle,
radius = 50, spiralDepth, turns = 4,
exponent = 0.685, start_angle = 0) =
let (fx = exponent < 0 ?
pow( max(0, 1-angle), 1/abs(min(-1, exponent-1) )) :
pow( max(0, 1-angle), max(1, exponent+1) ),
depthVar = (angle * spiralDepth)
)
[(radius * fx ) * cos(start_angle +
angleturns360sign(turns)),
(radius * fx ) * sin(start_angle +
angleturns360sign(turns)),
depthVar];
for (angle = [0 : 1/spiralNumSegments : jCeiling]) {
hull() {
//echo(angle);
translate(L_Spiral (angle,
spiralRadius, -spiralHeight, numTurns,
exponent, 0 ))
linear_extrude(angle * spiralHeight)
circle(d = sphereDiameterOne);
translate(L_Spiral (angle + 1/spiralNumSegments,
spiralRadius, -spiralHeight, numTurns,
exponent, 0 ))
linear_extrude(angle * spiralHeight)
circle(d = sphereDiameterTwo);
} // hull()
} // for j
} // plotSpiral()
spiralWidth = 30;
spiralDepth = 5;
///*
difference() {
// Subtract the spiral from the cube
translate([-spiralWidth/2, -spiralWidth/2, 0])
color("red", 0.3)
cube([spiralWidth, spiralWidth, spiralDepth*2]);
translate([0, 0, spiralDepth*2 ])
plotSpiral(spiralWidth, spiralDepth*3, snakeSides=5);
} // difference
//*/
//translate([0, 0, spiralDepth2 ])
// plotSpiral(spiralWidth, spiralDepth3, snakeSides=5);
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Yes it's always a good idea to set up your negative objects so that they
extend beyond the surface a bit.
The other issue with your script was that the top face of your spiral
cutout was not flat.
The second linear_extrude did not account for the additional translation
amount, it should be:
linear_extrude((angle + 1/spiralNumSegments)* spiralHeight)
Still not sure why that completely broke the hull, but changing just that
line by itself fixes the render (preview is still patchy without the added
z offset, but that is expected).
On Fri, Dec 17, 2021 at 2:42 PM Jim Witte jim.witte@gmail.com wrote:
Well, I moved the spiral a bit higher, changing the bit inside the
difference to:
translate([0, 0, spiralDepth*2+0.1])
plotSpiral(spiralWidth, spiralDepth*3, snakeSides=5);
And it worked. Before I guess it just didn't quite go through the top of
the cube, and I guess that screws up the hull for some reason.
On Fri, Dec 17, 2021 at 2:49 PM Michael Möller private2michael@gmail.com
wrote:
sitting here with the mobile on the bus, but
linear_extrude(angle * spiralHeight)
circle(d = sphereDiameterOne);
why not just cylinder(h=angle*spiralHeight, d=sphereDiameterOne)
Msquare
fre. 17. dec. 2021 20.41 skrev Jim Witte jim.witte@gmail.com:
I have the following program, that is meant to construct a spiral that
gets progressively deeper, by using hulls between successive extrusions of
the circles that make it up. (A circle is extruded, then hulled to the
next one, etc). This is then subtracted from a cube.
If I uncomment the plotSpiral() command at the bottom (without the
difference), it renders as I expect. But with the difference, it
differences the extrusions, but not the hulls between them. So the inside
of the spiral, where the individual extrusions overlap, it works like I
want (sort of), but on the outside, I just get a series of individual
pockets.
I could change the angle spacing as I get further out (that would look
cleaner too), but that would take longer, and this whole thing will be done
with a ball-nose end mill anyway, which should smooth it out on it's own.
Does anyone have any other ideas of how to get a "deepening spiral"
design?
Thanks,
JIm
module plotSpiral(spiralWidth, spiralHeight = 0, spiralThickness = 1,
snakeSides = 5) {
// Number of sides of the "snake"
$fn = snakeSides;
bumpiness = 1;
segmentsPerTurn = 35;
numTurns = 4;
numTurnsToPlot = 4;
// *** Derived ***
jCeiling = 1/numTurns*numTurnsToPlot;
sphereDiameterOne = spiralThickness/bumpiness;
sphereDiameterTwo = spiralThickness/bumpiness;
//spiralWidth = 30;
//spiralHeight = 100;
spiralNumSegments = segmentsPerTurn * numTurns;
spiralRadius = spiralWidth/2;
exponent = 1.685;
//ORIG: exponent = 1.685;
function L_Spiral (angle,
radius = 50, spiralDepth, turns = 4,
exponent = 0.685, start_angle = 0) =
let (fx = exponent < 0 ?
pow( max(0, 1-angle), 1/abs(min(-1, exponent-1) )) :
pow( max(0, 1-angle), max(1, exponent+1) ),
depthVar = (angle * spiralDepth)
)
[(radius * fx ) * cos(start_angle +
angleturns360sign(turns)),
(radius * fx ) * sin(start_angle +
angleturns360sign(turns)),
depthVar];
for (angle = [0 : 1/spiralNumSegments : jCeiling]) {
hull() {
//echo(angle);
translate(L_Spiral (angle,
spiralRadius, -spiralHeight, numTurns,
exponent, 0 ))
linear_extrude(angle * spiralHeight)
circle(d = sphereDiameterOne);
translate(L_Spiral (angle + 1/spiralNumSegments,
spiralRadius, -spiralHeight, numTurns,
exponent, 0 ))
linear_extrude(angle * spiralHeight)
circle(d = sphereDiameterTwo);
} // hull()
} // for j
} // plotSpiral()
spiralWidth = 30;
spiralDepth = 5;
///*
difference() {
// Subtract the spiral from the cube
translate([-spiralWidth/2, -spiralWidth/2, 0])
color("red", 0.3)
cube([spiralWidth, spiralWidth, spiralDepth*2]);
translate([0, 0, spiralDepth*2 ])
plotSpiral(spiralWidth, spiralDepth*3, snakeSides=5);
} // difference
//*/
//translate([0, 0, spiralDepth2 ])
// plotSpiral(spiralWidth, spiralDepth3, snakeSides=5);
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