A work in progress showcase: dovetail function
W W
```py
from openscad import *
nimport('https://raw.githubusercontent.com/wiw-pub/ztools/refs/heads/main/src/ztools.py')
def y_dovetail_cut(solid, dovetail_big_width, dovetail_small_width, dovetail_height, base_offset, epsilon=0.1):
'''
Perform dovetail cut across the y-axis. Inspired by traditional Japanese joinery.
Precondition: solid is already positioned on the z axis where top part will have dovetail, and the bottom will not.
When the solid saddles across +z and -z, the -z part of the solid is taken as a base where the dovetail does not apply.
Instead, the -z part of the solid can have an extension applied for the "female" part of the dovetail joint. This is typically done for stability.
Parameters:
solid: input solid to be dovetail cut.
dovetail_big_width: the width of the larger dovetail trapezoid.
dovetail_small_width: the width of the smaller dovetail trapezoid.
dovetail_height: Perpendicular span of the dovetail trapezoid.
base_offset: Positive offset extending base for the "female" part of the dovetail (negative not yet supported).
epsilon: Optional param to combat z-fighting.
'''
def dovetail(h):
'''
Helper method to create dovetail base shape.
'''
# trapezoid
pts = [
[-dovetail_big_width/2, 0],
[dovetail_big_width/2, 0],
[dovetail_small_width/2, dovetail_height],
[-dovetail_small_width/2, dovetail_height],
[-dovetail_big_width/2, 0]
]
trap = polygon(pts).rotz(90).linear_extrude(h)
trap = center(trap, axis=[1, 1, 0])[0]
return trap
mn, mx = bounding_box(solid)
_, _, dovetail_h = mx
# Finishing detail: Shape the dovetail to be flushed with the input solid.
dovetail = dovetail(dovetail_h) & solid
# Preprocessing to hollow out where dovetail would sit.
hollow = solid - dovetail
# Slice the bottom for base offset.
top, bottom = z_bisect(hollow)
# Cut left and right.
left, right = y_bisect(hollow)
# Override right with the larger base_offset.
_, b_right = y_bisect(bottom.right(base_offset))
b_right = b_right.left(base_offset)
# Attach dovetail to and mask the base offsets.
# Epsilon for z-fighting.
male = (left | dovetail) - b_right.scale([1 + epsilon, 1 + epsilon, 1])
female = right | b_right
return [male, female]
kw = {
'solid': cube([50, 20, 5], center=True).rotz(10).roty(10),
'dovetail_big_width': 10,
'dovetail_small_width': 5,
'dovetail_height': 10,
'base_offset': 5
}
l, r = y_dovetail_cut(**kw)
show([l.left(20), r.right(20)])
```
Raymond West
Hi,
The dovetail was invented years ago, being a simple method of making a strong, interlocking joint in wood, using hand tools. In that situation, you are usually starting with two separate items to be joined. I expect, in 3d printing, you have one large item, that you need to split apart, so the parts fit into the printer. It is a different situation, using different materials, etc. There are better ways of doing that, and simpler methods of connecting plastic 3d printed parts.
However, I was not able to run your script, but I would suggest you add an adjustable tolerance/clearance factor if you want other users to be able to use it on other printers/materials. When you have the male part of the dovetail, use offset, to get a larger shape, and use that to generate the female part.
hth,
Best wishes,
Ray
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W W
> There are better ways of doing that, and simpler methods of connecting plastic 3d printed parts.
Raymond West
You use tolerances as a parametric value. There are test prints, or simple enough to generate, for you to try with your printer. Then you use that as a default, but be prepared to vary it. No matter what you use, wood ground steel, titanium, concrete,you can never fit a rod into exactly the same diameter hole. In openscad, where that is tried, you sometimes get 'z-fighting'.
A stronger joint would be a mortice and tenon, with solvent adhesive or a peg through it. But, it depends on the shapes you are trying to join, and if it needs to be dismantled.
Here is a simple part solution, Parametric. The cylinders could be made into cones. Having multiple joints, instead of one large one, increases the surface area for adhesive, takes less length for the same interfacing length, etc. of course, instead of the cylinders, you could use dovetail shapes, but avoid sharp corners. (at a larger scale I'd fillet the sharp corners where the circles meet the slab).
############################################
from openscad import *
# circular lugs join
edge=50 #length of edge to be joined
leng= 30 # distance of overlap
num=5 # number of lugs
diam= edge/(num*2) #diameter of lugs
tol=0.2 # tolerance for fitting
th=10 # thickness of joint
dist= leng+(diam/4)
base= square([leng,edge])
fn=200
def lugs():
j = diam
all=[]
while j < edge:
all.append(
circle(d=diam).translate([leng + diam/3, j, 0])
)
j += diam * 2
return union(*all)
#lugs().show()
ma=union(base,lugs())
male=ma.linear_extrude(th)
male.show()
fe= ma.offset(tol)
#fe.show()
fe2= fe.linear_extrude(th+20)
female=
difference(base.right(leng).linear_extrude(th),fe2.down(10))
female.show()
##########################################################
Guenther Sohler
W W
> it appears there is a small gap, when putting the things together. is that intentional ?
@ray
> You use tolerances as a parametric value ... No matter what you use, wood ground steel, titanium, concrete,you can never fit a rod into exactly the same diameter hole.
Parameterizing the tolerance isn't the complex part I was thinking about. The complexity is abstracting that out, e.g., user specify nozzle size and the function can auto-calculate the tolerance on your behalf by default.
For the pet project I am doing, I prefer not to use adhesive if possible. It may need to be occasionally dismantled. But not the end of the world...I can always reprint the parts.
W W
W W
However, it doesn't matter when printing, because the z-fighting artifacts are so thin due to small epsilon. The slicer simply removes them.
