3D CAD:
GT2 pulleys for focusing a camera lens

Contents:

1. Calculating number of teeth
2. CAD of 15 teeth pulley, part 1
3. CAD of 15 teeth pulley, part 2
4. CAD of 15 teeth pulley, part 3
5. CAD of 15 save and prepare to print, part 4
6. CAD of 174 teeth pulley, part 1
7. CAD of 174 teeth pulley, part 2
8. CAD of 174 teeth pulley, part 3
9. CAD of 174 save and prepare to print, part 4
10. CAD of 174 clean from support material, part 5
11. CAD of 174 new version, part 6
12. CAD of 174 slicing and printing, part 7
13. CAD of 12 and 15 teeth, new design, part 1
14. CAD of 12 and 15 teeth, printing, part 2
15. CAD of 180 teeth pulley, part 1
16. CAD of 180 teeth pulley, part 2
17. CAD of 180 teeth pulley, part 3
18. To be continued

Note:
I take no responsibility or liability for what are written here, you use the information at your own risk!

6, CAD of 174 teeth pulley, part 1:

Now it's time to CAD the big pulley that will sit around the focus barrel of the lens.

Make a pulley as big as possible:

Because of the limited angle the focus rotate when focusing I need a high gear ratio. The small pulley can't have too small diameter because of the belt. The big pulley around the lens' focus barrel I can make bigger. It must sit around the white part of the barrel, but I have more space for it more to the right. Where the left arrow is the free distance is 11 mm, where the right arrow is the free distance is 23 mm. I have to design a pulley that has its hub translated about 10 mm relative the part of the pulley where the teeth are.

I tested with different parameters to optimize the pulley for maximum number of teeth. I found that 174 teeth was the maximum I can fit on the wheel.

The computer take very long time to draw the pulley up on the screen when there are so many teeth. My computer is an older I7 with 16 GB RAM. Strange, when I CAD 15 years ago already 1MB RAM was a lot.

Make the inner diameter bigger to fit camera lens:

I have to increase the hole to fit the barrels diameter, 70.1 mm.

Next step is to have the side of the pulley that is directed to the front of the lens to be a bit wider.

I place another 80 mm hole on top of the first hole. After that I place a third 95 mm hole on top of these holes.

Now the computer gave up, too much details to hold together. I got stuck here and must figure out a solution. Consulting my friend, he told that the version 0.18 has a lot of problems, upgrade to version 0.19.

It was not easy to find this new version, but here it is:

• https://github.com/ FreeCAD/ FreeCAD/releases/ tag/0.19_pre (https://github.com/ FreeCAD/ FreeCAD/releases/ tag/0.19_pre, FreeCAD web)

After this upgrade FreeCAD is working much better, no problem to work with the many teeth pulley.

Reduce the outer diameter:

On the side that points to the camera I want to reduce the outer diameter. I switch over to Part mode.

Make a tube.

Change the size of it. This will be a ring that I subtract from the pulley.

What's left after the subtraction. For details, see the earlier 15 teeth pulley.