# Bevel gear design & usage

The problem : I need to create a mechanism with 2 parallel shafts, at some distance apart, rotating in the same direction, either clock- or anticlock-wise.

The distance (> 1m) makes it impractical to set a chain of gears between the shafts, so my approach is to have a third shaft at 90 degrees with bevel gears; the driving motor could attach to this third shaft. It has been pointed out to me that a pulley-belt approach could also be used, but the distance between the parallel shafts makes me prefer the 90-degree shaft approach.

Not being a mechanical engineer, I tried to understand a bit more about bevel gears, and found out there are straight, spiral and other types. The 3D library I'm currently using for generating the gears creates angled teeth.

So here's the 1st question : for any type of bevel gear except the straight ones, does the geometry of the teeth have any impact on the direction of rotation ?

Since I don't want different rotation speeds on the parallel shafts, and there is no constraint on the rotation speed of the third, 90-degree shaft, so far my plan is to create gears with identical sizes (number of teeth).

And here comes the 2nd question : Should I use larger or smaller gears ? What's the impact of the number of teeth on the gear operation for the bevel gears ?

As a side note, I plan to 3d-print these gears for the prototype, so any comment that can factor this in is highly appreciated.

• What range of rpm are you working with? May 21, 2019 at 15:20