GT2, GT3 and GT5 Timing Gear Creator

Need help, or want to share a macro? Post here!
User avatar
looo
Posts: 3427
Joined: Mon Nov 11, 2013 5:29 pm

Re: GT2, GT3 and GT5 Timing Gear Creator

Postby looo » Wed Apr 08, 2020 8:12 am

Ok, some more inspections of the geometry gives some more hedeache:

Regarding the script:

....
# r0 - Inner circle radius
# r1 - Side circle radius that define the side of a tooth
# rs - Small circle radius that define the corner of a tooth
...

'r0': 0.555,
'r1': 1.0,
'rs': 0.15
But creating a gt2 timing gear I see some differences:
Bildschirmfoto von 2020-04-08 10-05-58.png
Bildschirmfoto von 2020-04-08 10-05-58.png (35.8 KiB) Viewed 440 times
Are the diameter of the arcs somehow related to other parameters like number of teeth?
User avatar
looo
Posts: 3427
Joined: Mon Nov 11, 2013 5:29 pm

Re: GT2, GT3 and GT5 Timing Gear Creator

Postby looo » Wed Apr 08, 2020 10:10 am

I get this geometry when applying tangential constraints and use the diameters as given (still there is one dof open). Befor copying the timing gear generator to freecad.gears I would like to make sure we have a correct geometry, So if anyone comes across a good drawing of a timing gear, please add a link to this topic.
Bildschirmfoto von 2020-04-08 12-06-28.png
Bildschirmfoto von 2020-04-08 12-06-28.png (32.85 KiB) Viewed 425 times
kisolre
Posts: 2258
Joined: Wed Nov 21, 2018 1:13 pm

Re: GT2, GT3 and GT5 Timing Gear Creator

Postby kisolre » Wed Apr 08, 2020 3:17 pm

Here are some drawings for a belt. This is what should be searched. The geometry of the belt that will ride on the gear. Or at least I think that :)
Attachments
large.jpg
large.jpg (35.11 KiB) Viewed 409 times
belt-tolerence.jpg
belt-tolerence.jpg (73.93 KiB) Viewed 409 times
gt2-timing-belt-11.jpg
gt2-timing-belt-11.jpg (11.82 KiB) Viewed 409 times
User avatar
looo
Posts: 3427
Joined: Mon Nov 11, 2013 5:29 pm

Re: GT2, GT3 and GT5 Timing Gear Creator

Postby looo » Wed Apr 08, 2020 3:55 pm

thanks. Still, there are some differences compared to the gt-macro:
Bildschirmfoto von 2020-04-08 17-49-57.png
Bildschirmfoto von 2020-04-08 17-49-57.png (91.34 KiB) Viewed 404 times
Feel free to review.
Attachments
gt_sketcher.FCStd
(25.83 KiB) Downloaded 15 times
chrisb
Posts: 26939
Joined: Tue Mar 17, 2015 9:14 am

Re: GT2, GT3 and GT5 Timing Gear Creator

Postby chrisb » Wed Apr 08, 2020 5:55 pm

From other belts (DIN 7721-1) it seems that the pulleys are not exact counterparts of the belt. Misumi offers the GT2 pulleys as CAD downloads. Anyone having an account there?
UR_
Posts: 1188
Joined: Tue Jan 03, 2017 8:42 pm

Re: GT2, GT3 and GT5 Timing Gear Creator

Postby UR_ » Thu Apr 09, 2020 11:03 am

Because timing belt pulleys are manufactured by hob milling, I think resulting tooth profile isn't made of any lines or arcs.


phpBB [video]
kisolre
Posts: 2258
Joined: Wed Nov 21, 2018 1:13 pm

Re: GT2, GT3 and GT5 Timing Gear Creator

Postby kisolre » Thu Apr 09, 2020 11:11 am

Involute in gears is made with trapezoidal tool profile. With right tool you can make any profile with arcs, ...
User avatar
looo
Posts: 3427
Joined: Mon Nov 11, 2013 5:29 pm

Re: GT2, GT3 and GT5 Timing Gear Creator

Postby looo » Thu Apr 09, 2020 12:45 pm

So you are saying that the belt-profile should be used to compute gears profile? Similar to involute gears.
User avatar
looo
Posts: 3427
Joined: Mon Nov 11, 2013 5:29 pm

Re: GT2, GT3 and GT5 Timing Gear Creator

Postby looo » Tue Jul 14, 2020 9:20 pm

gives a slightly different result compared to the macro:
(red = macro)


But still, there is quite some difference to the sketch posted above.
Attachments
Bildschirmfoto von 2020-07-14 23-20-49.png
Bildschirmfoto von 2020-07-14 23-20-49.png (13.29 KiB) Viewed 181 times