Help on drawing a worm gear with its involute gear

[NormandC]

Importing an OpenScad file in FC will generate proper Features, not tessellated objects.

I admit I should have tested the aforementioned solution before replying. But what you are saying is not always true. Some functions in OpenSCAD have no equivalent in FreeCAD (or any other CAD program for that matter), such as Hull and Minkowsky. In those cases, the process goes through meshing between OpenSCAD and FreeCAD.

I updated to openscad-nightly since the script requires a recent build, and opened globoidworm.scad; I'm waiting for FreeCAD to process it.

[qurn]

Importing an OpenScad file in FC will generate proper Features, not tessellated objects.

Oh, i didn't knew that, thanks. With this you can disassemble the teeth, the hole and everything.
However i would still call the sweep tessellated. The resolution can be changed in the code.

worm-gear.png (53.22 KiB) Viewed 2569 times

... economic constructions ...

Yes, i found a lot of resources about any kind of worm gears that make any kind of compromises either for the tools in order to make them or make the life easier for the person constructing it.

But this one is a real globoid worm drive. It can transmit the biggest force compared with the other types of worm drive, with same volume. Making it the perfect choice for 3D-Printing.

[NormandC]

However i would still call the sweep tessellated.

There is no sweep function in OpenSCAD, so it is generated manually. From reading the Naca_sweep script (mind you, I am in no way an OpenSCAD expert ), it looks like it generates the sweep by rotating a series of polyhedrons. See, that's the problem with OpenSCAD - it's not based on a "real" CAD kernel, but on CGAL, a library of mathematical algorithms designed for academia. CGAL was never intended for designing manufactured parts.

I waited for FreeCAD to open the scad file and generate the shape but had to kill the process. My system was telling me every 30 seconds that FreeCAD was not responding, do I want to wait or quit?

Then I tried OpenSCAD AddOpenSCADElement tool. I pasted the globalworm.scad script, and changed the paths to the shortcuts.scad and Naca_sweep.scad scripts to absolute paths. Then I clicked the "Add" button and waited... and waited... and waited

Finally I had the result. Upon studying the tree, I found this shape is what generates the threads for one of the gears:

FC_globalworm_scad_script_01.png (86.48 KiB) Viewed 2556 times

As you can see, it is a simple solid shape that cannot be edited (polyhedron001 is the other half). I wouldn't be surprised if it were actually generated as a mesh, then converted as a solid.

And finally, the last nail on the coffin: if saved as a FreeCAD document, the filesize is a whopping 54MB!!!

[meme2704]

Salut
Without laughing, I would like to see the face of the wheel that trains it

[foadsf]

I had the same question, came across this thread and like to share a good solution i found on the way.

Here is a parametric globoid worm gear drive for OpenSCAD.
https://www.thingiverse.com/thing:2776688

It's nicely written. It explains the way to get geometry in the gif.
To import it in FreeCAD OpenSCAD Workbench paste the content of the 3 .scad files and adapt the parameters.

Pros: easy, fast, precise, good documented
Cons: won't be a native FreeCAD object.

Unfortunately, I can't import the OpenSCAD's .scad files into FreeCAD. I have explained the issue here in details.

my environment is:

OS: Windows 10
Word size of OS: 64-bit
Word size of FreeCAD: 64-bit
Version: 0.18.16131 (Git)
Build type: Release
Branch: releases/FreeCAD-0-18
Hash: 3129ae4296e40ed20e7b3d460b86e6969acbe1c3
Python version: 3.6.6
Qt version: 5.6.2
Coin version: 4.0.0a
OCC version: 7.3.0
Locale: English/UnitedStates (en_US)

[Kunda1]

@keithsloan52 could you possibly weigh in on this ?

[fcaduser]

This topic connects one I already submitted. At some point we will need a tool generating surface defined with parametric curves (having a precise mathematical expression) and approximating with adequate nurbs. This is already the case with involute gear.

https://forum.freecadweb.org/viewtopic.php?f=8&t=37502

[keithsloan52]

@keithsloan52 could you possibly weigh in on this ?

Had a quick look.and I think it is not going to be easy to track down the problem.

1) If he cannot run any scad files then most likely is that FreeCAD does not know where OpenSCAD is installed.
See setting in OpenSCAD workbench preferences.

To test if things are setup correctly he should use OpenSCAD to export a simple scad file (i.e. One of OpenSCAD's
examples) to a CSG file and try opening that in FreeCAD.

2) Having said that looking at https://www.thingiverse.com/thing:2776688
There are three scad files, two are includes so really only one that could be imported into FreeCAD glowboidworm.scad.
I tried loading this into FreeCAD and it does look like there is a problem. I used OpenSCAD to export it as a CSG file
and inspected it. There are some very large polyhedrons so I isolated one and exported to csg and that loads okay.The cutdown polyhdron file is

polyhedron.csg

(105.94 KiB) Downloaded 50 times

The glowboldworm csg file is too large, one needs to get the scad file from thingiverse and use OpenSCAD to export as a CSG
( That is what FreeCAD does under the covers ) Might just take a very long time to load and need to keep clicking to carry on when it prompts about aborting.

3) I note that the info on Thingiverse says it needs OpenSCAD 2018.16. I only have 2015 but it seem to load okay in OpenSCAD.

I have a lot on at the moment but will try and find some time next week.

[keithsloan52]

As you can see, it is a simple solid shape that cannot be edited (polyhedron001 is the other half). I wouldn't be surprised if it were actually generated as a mesh, then converted as a solid.

Nope : OpenSCAD polyhedrons are constructed as Part::Polygons and Part::FilledFaces. The reason it looks mesh like is that
OpenSCAD is creating the gears as very large polyhedrons. Using OpenSCAD export the scad file as a CSG and look at the number of
vertext in the polyhedrons, nothing FreeCAD can do about that.

[keithsloan52]

Okay I was about to leave the import of the CSG version running overnight.
It started at 22:48
Stuff started to appear in the display window at 22:54 and completed at 22:56
So 12 mins.

Looks just the same as @qurn had produced in an earlier post.
https://www.dropbox.com/s/9wkega8jkc2wa ... FCStd?dl=0