If the outside shape doesn’t matter, why not just make it a cylinder with
the threaded shape differenced away?

Am I missing something in your question?

Steve

On Wed, 11 Dec 2024 at 14:38, Raymond West via Discuss <
discuss@lists.openscad.org> wrote:

That gives a cylinder with a hole the shape of the outside of the piece,
and a 'plug' inside that hole the same shape as the inside of that piece.

I'm thinking maybe use projections at 0.1mm  heights, then offsets and
linear extrudes. Probably good enough resolution for this in fdm
printing. But, I've solved this specific case, but looking for a more
general solution.

On 11/12/2024 23:44, Steve Lelievre via Discuss wrote:

I'm still waking up, so I may not be entirely thinking clearly, BUT...

If you take that part and first difference from a cube or cylinder, it will
then remove the entire part and leave a plug in the middle.  Then remove
the plug in the middle.  Next expand the walls of the diff by a small bit
and then add the original part back in. This will leave the inside the same
shape as the original, but make the outside much bigger. There is likely
similar dance steps you can do, but it is WAY to much work IMNSHO.  Having
something that could do a Minkowski Sum, and then edit/remove all faces
that are pointing inward.

Just a thought WAY to early in the morning...

On Thu, Dec 12, 2024 at 6:21 AM Raymond West via Discuss <
discuss@lists.openscad.org> wrote:

On 12/12/24 06:21, Raymond West via Discuss wrote:

Maybe the thinking is basically wrong. This pictured thread looks like
it was formed by a sine wave, and the tap and die to create it doesn't
exist.  I needed some screws for a woodworkers bench vise.  I started
with a 2d polygon that describes the tooth shape, tilt it a few degrees
so there is no steps when a for loop wraps it around a cylinder.  That
then is the basic shape I carve on a 4 axis mill with a wedge under the
spindle motor to make the 7 degree working face of a buttress thread.

Then to print the half nuts,  I make it again but .45mm bigger in
diameter and diff that from a block to make the half nut I print 2 of.
The mill is using a 1/16" rn tool and small enough steps on the back, no
load face of the thread is smooth. I carve a 4mm tall, 6mm long  tooth
on a 12mm pitch, rotate the stick 180 degrees and reverse everything,
carving a 2 start thread. The stick is hard maple, the nuts have about
12 teeth engaged, several times stronger than the conventional screws
with wooden nuts you can get for $200 on fleabay. And I've described it
all in two paragraphs.

Quit thinking inside the box. Way too restrictive. OpenSCAD can do it if
you can think it.

Wall thickness is normally a function of the slicer used. No need to
mess with the dimensionless .stl, make them as thick as you need.  Or am
I missing something?

Cheers, Gene Heskett, CET.

"There are four boxes to be used in defense of liberty:
soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author, 1940)
If we desire respect for the law, we must first make the law respectable.

• Louis D. Brandeis

On Thu, 12 Dec 2024 at 03:21, Raymond West via Discuss <
discuss@lists.openscad.org> wrote:

Oh yes, silly me.

If we had a way to remove voids (cavities) you could just cap the shape
with a cube, remove the void, scale and then subtract the original and the
cap,

I can see how to go that using an external program but I don’t know how in
OpenSCAD itself.

Steve

On 11/12/2024 23:44, Steve Lelievre via Discuss wrote:

Hi Ray,

If you can send me the stl file i can try something here.

Basically stl are triangles.

If all the points can be are made to project on to another surface (maybe a
cylinder), it can give the thicken effect.

Regards
Sanjeev

On Thu, 12 Dec, 2024, 4:08 am Raymond West via Discuss, <
discuss@lists.openscad.org> wrote:

Thanks for your suggestions. A bit of a moot point, since I'd replaced
the threads with my own, but useful results for maybe other situations.

I found I could simply scale it a few times, and add to original. I've
also included the code to thicken the walls, which could be useful for
thin partitions in a box, say.  Much quicker than Minkowski (but only
deals with sides, which may or may not be a good thing). I've shown a
section on the scaled version (the cube differenced). I'm not concerned
with the top ridges, since the original was stupidly thin at the top.

module myshape(){

import("P:/Docs/openscad/partscrew.stl");
}

   difference(){
   myshape();
   cube(500);
   }

   top=120;
   bot=100;
   t=5;
   step=0.1;

translate([50,0,0])
widen(top,bot,t)myshape();

module widen(top=2,bot=1,t=10){  //widens all walls
   translate([0,0,bot])
  echo(top,bot,t);
     for (j=[bot:step:top]){
     echo(j);
      translate([0,0,j])
          linear_extrude(step+step)
          offset(delta=t)
          projection(cut=true)
          translate([0,0,-j])
          children();
    }
}

//try scaling  widens outside only

 translate([100,0,0]){
   difference(){
     union(){
      myshape();
       scale([1.2,1.2,1.0]) myshape();
       scale ([1.1,1.1,1.0]) myshape();
    }
   cube(500);
  }

}

On 12/12/2024 16:36, Sanjeev Prabhakar wrote: