Helical Gear tutorial?

[Bas_Goris]

See my post : Helical Gear tutorial?
I suggest to use the filament of Igus like iglidur i150 or i180. See https://www.igus.eu/info/3d-printing.

[Bas_Goris]

To be continued on:

Why this difference with Solid Difference?

Hi, Why this difference with Solid Difference? The blue gear has a drain in the middle, but the (almost) identical pink gear is missing the drain. Why and how to solve this on a generic way? See attached the gh file. (sorry, the file is very slow because of the rail revolve command and the solid difference command) HerringBoneGearsV1.3_WIP.gh (111.8 KB) PS In this case it is a mirror, but in many cases it will not. Cheers Bas [image]

[Bas_Goris]

I want to share this script by Seghier in this post:

Why this difference with Solid Difference?

Test and improve it if you want gear4.gh (19.9 KB)

I hope someone takes the effort to improve your script for gears with different number of teeth, and an option for external gear; a rack; and internal gear. My skills in Python are not so good.

[saucerdesigner]

@Ian

Draw onto the “paper strip” the lines of the tooth points at the correct bevel angle.

Ian, did you mean “at the correct helix angle”?

[Ian]

Oh, yes, sorry, that was a slip-up. Just to say though, I ended up confused about the geometry. Others with more ability than me (I’m referring especially to the helical gear macro within the “Gear Workbench” by “Looo” in FreeCAD) produce a helical gear that does not agree with the olden days method above; but when Looo’s gear is compared to a commercially created 3D-model, such as by Rush Gears, theirs do agree. So I abandoned the paper strip method and myself just went and used the Gear Workbench within FreeCAD. Maybe one day, someone with the skills can import Looo’s open source macro into a Rhino version.

https://wiki.freecadweb.org/FCGear_Workbench

[saucerdesigner]

@Ian

beta = helix angle

I’ve copied and pasted the code for Scripted gears from the Github link into a python 3.2 script and when run it reports: “ImportError: No module named FreeCAD”. Where can I find the FreeCAD module? Thanks.

I thought I’d found it but was mistaken. Still searching the web for clues on how to make this work on Win 10
Thanks.
Edit: I was trying to run just a piece of the gears script from PyScripter, an external Python IDE. On the FreeCAD forum I was finally given the entire script and told you have to run the script from inside FreeCAD in the Macro console. What an awesome tool!

[Nosorozec]

The FreeCAD is standalone parametric CAD software.

[Ian]

Sorry, I entirely missed this post of yours. Apologies.

Anyhow, it seems you did eventually work it out – that the Gear Workbench module of FreeCAD, runs inside the FreeCAD 3D nurbs modelling app, a free download at https://www.freecadweb.org.

But for the benefit of others who may come across this thread, here’s a note on usage. Once you have installed FreeCAD, you make helical gears by the following steps:
File>New
View>Workbench>Gear
Select on toolbar ‘create involute Gear’
Where:
beta = helix angle
module = 1 / normal diametral pitch

[saucerdesigner]

Apologies for the tardy reply.
Here’s the Python code for the macro you need to create in FreeCAD.
Be sure that you change the path to reflect your FreeCAD installation…
begin copy code below

MODULE_PATH = ‘C:\Users\sauce\AppData\Local\FreeCAD 0.19\bin’ # correct location?

DBG_LOAD = True

if not MODULE_PATH in sys.path:
if DBG_LOAD is True:
print(“no module path”)
sys.path.insert(-1,MODULE_PATH)
else:
if DBG_LOAD is True:
print(“module path is present”)

if DBG_LOAD is True:
print(sys.path)

import FreeCAD
import freecad.gears.commands

FreeCAD.newDocument(“new_doc”)

gear = freecad.gears.commands.CreateInvoluteGear.create()
gear.teeth = 134
gear.beta = 15
gear.height = 10
gear.double_helix = False

FreeCAD.ActiveDocument.recompute()
FreeCADGui.SendMsgToActiveView(“ViewFit”)

end copy code above
Search the forum for help on using FreeCAD.
https://forum.freecadweb.org/

[PeterB]

Arraypolar the negative object around the cylinder then Booleandifference those obects to cut them away.

[oorlyg]

Got lost from point 4 to point 6. Can you place a few images for expanding the info?

[Ian]

I eventually moved away from the method that I explained above in September 2020. As I noted in my post of November 2020 above, I later favoured use of the module called “Gear Workbench” in FreeCAD, which provides a nice nurbs model. The reason I switched over is that the earlier method did not seem to be geometrically accurate.

This topic does seem to attract a fair bit of interest. It really needs someone with better math and scripting skills than mine to perhaps write a Rhino script. @Bas_Goris made one for Grasshopper, and I would leave it to him to vouch for the mathematical foundation of his approach and its accuracy. What I can say is that in the posts above, there are links to a good number of strong reference materials to look at.

One approach to creating a Rhino script, that would include a number of gear types, would be to begin with the “Gear Workbench” script for FreeCAD written by “looo” on Github (see my post of Nov 20 above for link).If someone were to replicate the FC Gear Workbench for the entire suite of gear types, as a Rhino script, note that for bevel gears there was a small shortcoming of Loos’s approach, a departure he made from standard bevel gear design technique, in that the pitch circle ought to be at the wide end of the gear – for the full explanation see the post, at FreeCAD forum – FC Gear Workbench bevel gear strange result – 28/Oct/2020