Prototype Using a Seven Tooth Pinion

Mon, 25 Feb 2013

Another page for the Gear Zine

This time about using mixed 2D and folded tooth gears. For gears with few teeth (in this case, 7) the faces of the teeth need to be curved. These are known as involute gears. I'm using double thickness card to construct 2D involute gears. 

I wanted three smaller gears spaced equally around a central gear so there was a bit of geometry involved 🙂

By adding the radii of the two gears I knew that the distance between the centre of the larger gear and each of the small gears was 57mm. I planned to make a T shaped base (in red above) Fitting the lower gear and first gear was simple, I just space them by the 57mm.

The other two require a little geometry. I'm spacing the pinions evenly round the central gear, so that is one every 120° 

That makes the angle opposite 'a' = 30° so I can work out height 'a' as sine 30° =0.5  

0.5 x 57mm = 28.5mm

Length 'b' is calculated the same way but this time with the angle being 60° 

sine 60° = 0.8660

0.8660 x  57mm = roughly 49.5mm


With piece the parts laid out, here's how it looks. Again I've made the support piece from the same colour card as well background so it blends in. 


…and here it is in a mock up of the zine so far.