Need help trying to recreate an old gear

Post here for help on using FreeCAD's graphical user interface (GUI).
Forum rules
and Helpful information
IMPORTANT: Please click here and read this first, before asking for help

Also, be nice to others! Read the FreeCAD code of conduct!
mconsidine
Posts: 125
Joined: Wed Jan 18, 2023 10:41 pm
Location: Randolph, VT USA

Need help trying to recreate an old gear

Post by mconsidine »

Hi,

Code: Select all

OS: Linux Mint 21 (X-Cinnamon/cinnamon)
Word size of FreeCAD: 64-bit
Version: 0.21.0.32435 (Git)
Build type: Release
Branch: master
Hash: 48a921d2b73fa6163571a71d7416d60f2bd7c2b2
Python 3.10.6, Qt 5.15.3, Coin 4.0.1, Vtk 9.1.0, OCC 7.6.3
Locale: English/United States (en_US)
Installed mods: 
  * ProDarkThemePreferencePack 1.0.0
  * toSketch 1.0.1
  * Alternate_OpenSCAD 1.0.0
  * Render 2023.2.2
  * Manipulator 1.5.0
  * Help 1.0.3
  * POV-Ray-Rendering
  * MeshRemodel 1.8919.0
  * freecad.gears 1.0.0
  * fasteners 0.4.55
  * Silk 1.0.0
  * Dracula 0.0.2
  * Curves 0.6.8
  * ThreadProfile 1.84.0
I am trying to recreate an old gear. The actual gear part can be handled by the Gear WB. It's the "interior" part that is challenging me. This gear has six spokes, each of which tapers a bit from the center and whose profile is an ellipse. Right now, I'd just be happy figuring out how to carve out the pie-shaped pieces, leaving the spokes to be dealt with via a fillet.

I've attached what I've got so far, after a few tries. What I'm trying to do is use an imported image as a template for a Sketch. In the sketch I constrained (not fully, I admit) the corners and connections. What I can't seem to figure out how to do is take the intersection of those lines, and extrude them to a solid that I can then multiply 6 times and cut from a disc.

I started using the Part WB and perhaps I should have started with Part Design. That said, can anyone give me some direction on getting the solid I'm looking for?

TIA,
mconsidine
Attachments
old_gear_test.FCStd
(150.5 KiB) Downloaded 22 times
Bance
Veteran
Posts: 4185
Joined: Wed Feb 11, 2015 3:00 pm
Location: London

Re: Need help trying to recreate an old gear

Post by Bance »

Try a tutorial or two.....

Tutorials

Specifically look at the sketcher tutorials.

Using circles in that fashion will not work, instead use arcs and connect with tangent constraints.
chrisb
Veteran
Posts: 53919
Joined: Tue Mar 17, 2015 9:14 am

Re: Need help trying to recreate an old gear

Post by chrisb »

As a follow-up to Bance's recommendations:

1) You can use the trim tool to remove the excesses
2) Either turn the image or just take it for the dimensions, but in any case you should create the cutout symmetric to the Y-axis (or X).
A Sketcher Lecture with in-depth information is available in English, auf Deutsch, en français, en español.
User avatar
papyblaise
Veteran
Posts: 7864
Joined: Thu Jun 13, 2019 4:28 pm
Location: France

Re: Need help trying to recreate an old gear

Post by papyblaise »

use the "Fillet" tool of sketcher to make the interior radii
In Part Wb you have to do boolean operations to build a uniform object
Attachments
gear.FCStd
(553.88 KiB) Downloaded 8 times
gear.JPG
gear.JPG (59.35 KiB) Viewed 568 times
mconsidine
Posts: 125
Joined: Wed Jan 18, 2023 10:41 pm
Location: Randolph, VT USA

Re: Need help trying to recreate an old gear

Post by mconsidine »

Thank you all for the pointers. I had overlooked the Trim function and appreciate the workflow description.
mconsidine
User avatar
thomas-neemann
Veteran
Posts: 11800
Joined: Wed Jan 22, 2020 6:03 pm
Location: Osnabrück DE 🇩🇪
Contact:

Re: Need help trying to recreate an old gear

Post by thomas-neemann »

mconsidine wrote: Wed Mar 22, 2023 10:23 pm ...
if this is a solution for you, i can link a video to it
Bildschirmfoto_2023-03-23_10-01-37.png
Bildschirmfoto_2023-03-23_10-01-37.png (45.15 KiB) Viewed 510 times
old_gear_test-tn.FCStd
(152.97 KiB) Downloaded 8 times
Gruß Dipl.-Ing. (FH) Thomas Neemann

https://www.youtube.com/@thomasneemann5 ... ry=freecad
mconsidine
Posts: 125
Joined: Wed Jan 18, 2023 10:41 pm
Location: Randolph, VT USA

Re: Need help trying to recreate an old gear

Post by mconsidine »

@thomas-neemann A video link would be helpful. Thank you as well.
mconsidine
User avatar
thomas-neemann
Veteran
Posts: 11800
Joined: Wed Jan 22, 2020 6:03 pm
Location: Osnabrück DE 🇩🇪
Contact:

Re: Need help trying to recreate an old gear

Post by thomas-neemann »

mconsidine wrote: Thu Mar 23, 2023 11:12 am @thomas-neemann A video link would be helpful. Thank you as well.
mconsidine
here it is: viewtopic.php?p=670054#p670054
Gruß Dipl.-Ing. (FH) Thomas Neemann

https://www.youtube.com/@thomasneemann5 ... ry=freecad
User avatar
Shalmeneser
Veteran
Posts: 9474
Joined: Wed Dec 23, 2020 12:04 am
Location: Fr

Re: Need help trying to recreate an old gear

Post by Shalmeneser »

:idea:
Attachments
Capture d’écran 2023-03-23 122929.jpg
Capture d’écran 2023-03-23 122929.jpg (71.13 KiB) Viewed 429 times
old_gear_test-tn.FCStd
(152.97 KiB) Downloaded 5 times
chrisb
Veteran
Posts: 53919
Joined: Tue Mar 17, 2015 9:14 am

Re: Need help trying to recreate an old gear

Post by chrisb »

I have rebuilt the model in PartDesign, so you can see the differences, but finally it is a question of your personal preference whether you use Part or PartDesign. I like to take advantage of the simpler tree, because PartDesign always does the booleans automatically. At the same time I have placed the sketch as mentioned above.

There is a good reason why I so strongly recommend to fully constrain your sketches: it can reveal flaws in your design. Here is one:
SnipScreenshot-2a1c7d.png
SnipScreenshot-2a1c7d.png (7.25 KiB) Viewed 394 times
This should probably be tangent.

By appropriately arranging the features, I do the hole in the middle for all features at once.

If the big subtractive tube should be subtracted on both sides, I would recommend to center the gear, and do a mirror of the pocket.

(Due to the size limit I add only 5 cutouts)
SnipScreenshot-5a1b1e.png
SnipScreenshot-5a1b1e.png (52.08 KiB) Viewed 390 times
Attachments
old_gear_cb.FCStd
(998.52 KiB) Downloaded 6 times
A Sketcher Lecture with in-depth information is available in English, auf Deutsch, en français, en español.
Post Reply