**This Instructable is being entered in a competition. If you like it or find it helpful your support by vote would be greatly appreciated!**

In this instructable I hope to impart unto you what I have learnt about making bevel gears. If you know more on this subject please feel free to drop a comment below, all of this knowledge has been collected through my own theoretical work and so is NOT cutting edge. But the theory is sound and the gears print and work!

I won't be going into involutes however this methodology CAN be used to create involute gears as its simply a matter of placing your chosen tooth profile instead of the one used in this example.

With that said... Onwards!

## Step 1: Basic Gear Theory

As I'm sure you know, gears are designed to transfer power and motion. The idea is to take two simple cylinders which would otherwise slip when rolling against each other and add "teeth" to better control the motion and reduce loss.

**Module, P.C.D and Tooth Count**

P.C.D or Pitch Circle Diameter is basically the diameter of the cylinder as mentioned above. This is the diameter at which the teeth mesh. The Inner and Outer diameters are related to the size of the tooth with the P.C.D being halfway between the Inner and Outer diameters. We shall call it **D.**

Tooth Count is the number of teeth around a gear. We shall call it **N. N must ALWAYS be a whole number.**

Module is a factor that determines tooth size. The larger this number is, the larger the teeth. We shall call it **M.**

The three are related like so: **D** = **N** x **M**

Usually a module of 2 will do but the larger the module the better chance the gear will have to print.

So for example if we have a Pitch Diameter of 90mm and a Module of 3, our Tooth Count will be 30.

**Speed Ratios**

The speed of a second gear can be found using the speed of the first and the tooth count. If Gear A has twice as many teeth as Gear B, it stands to reason Gear B will rotate twice for every rotation of Gear A.

**Speed**A x **Teeth**A = **Speed**B x **Teeth**B

**Speed**B = (**Speed**A x **Teeth**A)/**Teeth**B

**Choosing your Values**

In most cases you'll be choosing your values by Tooth Count and P.C.D as your limitations will be size and speed ratio. Whatever approach you take, using their relationship will keep you right!

**Involute Gears**

As previously mentioned I won't go into too much detail. The general idea is to create teeth that will mesh perfectly by using geometry and some maths to create the perfect tooth profile. It really is difficult to sum up here so I will simply mention that these following videos should help a lot and you can apply the idea to this project!

I'm able to make the small gear, but getting lost when creating the Tooth Wedge for the larger gear.

The Fusion 360 files aren't viewable by me -- get a "Forbidden" error. Are you able to share it publicly?

Thank you again for sharing your efforts!

Hi,

i have trouble making the step 4 image 2.

How did you do the second triangle ? I have my 3 lines from the center to the outer triangle. I have try construction plan, with a rectangle but it does'nt work.

Hi Michael,

I'm new to this as well but I used the intersect tool from sketch->Project/Include->intersect to get correct reference points on the inner construction plane.

ok, so the PCD cone extending to the vanishing point along the intersection plane will intersect the inner tooth drawing at two points. This defines the total height of the inner end of the tooth. And is basically a scale of the original outer.

Now, the top point needs extending out at a tangent to form the base of the triangle as with the original profile. To do this you draw the same sector lines that you did to form the original profile (as the number of teeth doesn’t change the angle doesn’t change). Then extend out from the top point to these lines as before.

Now you’ll have the base of the triangle and the point, all that is left to do is to join them up.

Awesome! I voted for you, I will use these in my K2-SO costume instructables!