Hi,

I am trying to use the module
https://github.com/hugokernel/OpenSCAD_Dovetail/blob/master/dovetail.scad

I have written two modules part1 and part2, which I was hoping would be 2
parts that have been cut using dovetail somewhere down the vertical part of
the square tube.

It hasn't come out like I wanted.

Does anybody have any idea why it's not worked or can give me any kind of
advice please?

Thanks,

Richard.

I missed the attachment, sorry.

TL;DR:  put # in front of each cutter() invocation, and then look
carefully at the top of the transparent pink cutter.

First, I suggest that you carefully examine your base model.  It has a
bunch of Z-fighting in the funnel section that makes it unclear what's
really going on, but when you render it it looks like one side is
totally open.  Then the bottom of the funnel appears to be blocked.  (Or
is it just a shovel, not a funnel?)

Then... remember how you're asking it to cut.  You're going to end up
with a cut line roughly along the YZ plane, the X=0 plane, with the +Y
stuff in one part and the -Y stuff in the other part.  But look at your
model - it has almost nothing in -Y.  I suspect that you really want to
rotate the model 90° around X before cutting.

Next, put # in front of one of the cutter() invocations, and look
carefully at the shape it makes.

This is just part2(), with # in front of the cutter() call:

See those skinny triangular-ish shapes?  Those are dovetails.  But
there's only one tooth, and it's very wide and very shallow.

// Finally, setup the dovetail:
// - Teeth count
// - Teeth height
// - Teeth Clearance
teeth = [1, 8, 0];

Yep, one tooth, 8 units tall, and 250 units wide in X.  Something funky
is going on with those teeth, probably caused by the various ratios.

Let's flop the model on its back and try some different dovetail parameters.

In both part1() and part2():

    rotate([-90,0,0]) whole_model();

That requires rotating the bounding box too:

dimension = [250, 600, 150];

You kind of have to have the bounding box that big, so that the funnel
is inside of it, but it means that to get a reasonable tooth size you
have to have a lot more teeth.

teeth = [5, 8, 0];

Looking from +Z, orthogonal:

Hey, getting close.

Let's look at the two resulting parts, zoomed in on the joint, from +Z
in orthogonal mode...

Looking plausible.  I would be happier if the dovetail tooth was
narrower, but I don't immediately see a way to do that using this library.

You have it set for zero clearance.  Mathematically correct, but your
printer has slop; if you have zero clearance you'll never get the parts
together.  Experiment, but my guess is that you want about 0.1mm or
0.2mm.  The library's example is 0.5mm; that seems like more than
necessary.  You want a tight fit, especially on something like this
that's thin.

Actually printing this is not going to be fun, because those teeth are
going to be all overhang, not even bridges.  Unless you really intended
that funnel to be open on one side, it's not going to be fun in this
orientation.  The tube is better; 40mm is for me a long ways to bridge,
but not completely implausible.

You could print it vertically, and rotate the cutter so that it cuts
along the XY, Z=0 plane.  That might make it easier to print.

What I would probably do, though, is to take some design hints from
plastic rain downspouts.  Design in a couple of segments, printed
vertically (to avoid bridging).  Print the bottom part, with the angled
tube, upside-down so that the angled part is an overhang, but not an
awful one. Have the lower segments widen out a little at the top so that
the upper segments nest inside them.  (Not the other way 'round, if you
might handle water; you want the water to fall past the joint before it
has a chance to sneak through it.)  That gets you lots of surface to
glue, and may make it a support-free print.  I'm not sure what the
"resting block" is for; you might want to design so that it is at the
(as-printed) bottom of one segment or another, to avoid needing to
support it.

I hope that moves you along...