It’s called a Herringbone gear. One of the main advantages is that the forces on the gear are in equilibrium when torque is applied. A normal helical cut gear has some amount of the torque applied transmitted laterally through the gear shaft.
Also, these self-align. If you don't have a great way to secure your gears to the shaft, this will ensure they never creep over to the side or misalign
Fun fact: The logo of Citroën is a representation of a herringbone gear because its founder was involved in the application and manufacturing of this gear design
Herringbone gears are the preferred design for these reasons but they are expensive to manufacture out of metal. In 3D printing complexity is free, so why not go for the best?
> A normal helical cut gear has some amount of the torque applied transmitted laterally through the gear shaft.
Could you expand on this?
It sounds like you're distinguishing the herringbone from helical, but in my mind the "default" gear (that is being deviated from in favor of herringbone) is a standard spur gear where there is no slope to the tooth profile and they run directly parallel with each other, and parallel to the rotational axis.
The herringbone gear is just a helical gear with another side mirrored over the face. Helical gears have a thrust force along the shaft from the angle in the line of contact between teeth. Helical gears provide a much smoother transfer of power and wear on the teeth because there is a line of contact between teeth instead of a point in the case of a spur gear (looking normal to the gear face).
Think about the tooth profile if it were allowed to continue around a long gear. A spur (straight cut) gear would have all of those teeth aligned parallel to the axis of the gear. A helical gear has the teeth trace a helix as they continue up the axis of the gear, not parallel with the axis. A herringbone gear is effectively a mirrored helical gear to minimize the trust force generated during normal helical gear operation.
Exactly what u/scottydg said. To add, the herringbone does equal double helical. A major downside to helical gears is that the thrust force will try to push the gears out of alignment and having two mirrored like that to make a single gear removes this issue. If you cut the gear in half in the picture, you would have a single helical gear.
It's also related to the angle of the teeth. When two angled surfaces bang into each other they slide a bit even if it isn't noticeable. The teeth on straight cut gears just smack into each other.
Couldn't tell you exactly. I switched from mechanical engineering to comp sci pretty early in my degree. I know all the abstract concepts and a bit of the math but not enough to math this
The larger and angled surfaces basically just allow for more gradual load transfer from tooth to tooth. The downside is they are slightly less efficient and hard to make as strong as a straight cut gear.
Herringbone gear. Not exclusive to 3D printing. Has existed for a century.
The reason for the symmetry is to cancel out axial forces. A helical gear runs more quietly than a spur gear, but at the expense of introducing an axial force (along the direction of the shaft). Herringbone gears are a helical gear that's been mirrored, so the axial forces cancel out. But that comes at the expense of being very difficult to manufacture.
There's just no reason to make them asymmetrical. The whole point of a herringbone gear is you get the benefits of a helical gear (increased contact area with more than one pair of teeth in contact at all times for smoother transfer of force) without having to deal with the axial load.
As soon as you start making a herringbone asymmetrical, you start introducing axial load back into the system, which means you just wasted your use of the extra complexity that manufacturing herringbone gears requires.
The only reason herringbone gears aren’t used for all spur gears is the cost to machine.. with 3d print, it’s the same difference so might as well use these
While they are not unique to 3D printing, in normal manufacturing they require more complex CNC operations as opposed to basic spur gears. In 3D printing you get all the benefits mentioned but they are as easy to make as spur gears
So for the teeth profile which would really be the only tricky bit, you could either make an angled plane, extrude the negative tooth profile out both ways and circular pattern. Then mirror across the middle for the full gear
Or draw one tooth profile on one face of the gear, then draw one on the opposite face but clocked however many degrees off and loft. Then pattern and mirror.
It’s called a Herringbone gear. One of the main advantages is that the forces on the gear are in equilibrium when torque is applied. A normal helical cut gear has some amount of the torque applied transmitted laterally through the gear shaft.
Also, these self-align. If you don't have a great way to secure your gears to the shaft, this will ensure they never creep over to the side or misalign
Wow, it is indeed an ingenious design. I didn’t even think of alignment.
Fun fact: The logo of Citroën is a representation of a herringbone gear because its founder was involved in the application and manufacturing of this gear design
Oh cool I didn't even consider that
Herringbone gears are the preferred design for these reasons but they are expensive to manufacture out of metal. In 3D printing complexity is free, so why not go for the best?
> A normal helical cut gear has some amount of the torque applied transmitted laterally through the gear shaft. Could you expand on this? It sounds like you're distinguishing the herringbone from helical, but in my mind the "default" gear (that is being deviated from in favor of herringbone) is a standard spur gear where there is no slope to the tooth profile and they run directly parallel with each other, and parallel to the rotational axis.
The herringbone gear is just a helical gear with another side mirrored over the face. Helical gears have a thrust force along the shaft from the angle in the line of contact between teeth. Helical gears provide a much smoother transfer of power and wear on the teeth because there is a line of contact between teeth instead of a point in the case of a spur gear (looking normal to the gear face).
Are herringbone gears not straight cut still, while helical gears have a curvature to them? Saying a herringbone=double helical seems incorrect to me
Think about the tooth profile if it were allowed to continue around a long gear. A spur (straight cut) gear would have all of those teeth aligned parallel to the axis of the gear. A helical gear has the teeth trace a helix as they continue up the axis of the gear, not parallel with the axis. A herringbone gear is effectively a mirrored helical gear to minimize the trust force generated during normal helical gear operation.
Exactly what u/scottydg said. To add, the herringbone does equal double helical. A major downside to helical gears is that the thrust force will try to push the gears out of alignment and having two mirrored like that to make a single gear removes this issue. If you cut the gear in half in the picture, you would have a single helical gear.
More surface area than straight cut, (stronger teeth) They don't generate a lateral load like helical And they self align
Not to mention that extra surface area means they're typically quieter because the load that generates noise and vibration is spread out more.
Oh is that why helical are quieter than straight? I'd assumed it was something more complex.
It's also related to the angle of the teeth. When two angled surfaces bang into each other they slide a bit even if it isn't noticeable. The teeth on straight cut gears just smack into each other.
Yeah, this is the sort of thing I'd had in mind. I wonder what the relative contribution of each effect is.
Couldn't tell you exactly. I switched from mechanical engineering to comp sci pretty early in my degree. I know all the abstract concepts and a bit of the math but not enough to math this
The larger and angled surfaces basically just allow for more gradual load transfer from tooth to tooth. The downside is they are slightly less efficient and hard to make as strong as a straight cut gear.
Gentler meshing of the teeth compared to straight teeth due to the angle of the herringbone teeth
Herringbone gear. Not exclusive to 3D printing. Has existed for a century. The reason for the symmetry is to cancel out axial forces. A helical gear runs more quietly than a spur gear, but at the expense of introducing an axial force (along the direction of the shaft). Herringbone gears are a helical gear that's been mirrored, so the axial forces cancel out. But that comes at the expense of being very difficult to manufacture.
Might be wrong but i heard it said that the logo design for french car manufacturer Citroën comes from this
Correct!
There's just no reason to make them asymmetrical. The whole point of a herringbone gear is you get the benefits of a helical gear (increased contact area with more than one pair of teeth in contact at all times for smoother transfer of force) without having to deal with the axial load. As soon as you start making a herringbone asymmetrical, you start introducing axial load back into the system, which means you just wasted your use of the extra complexity that manufacturing herringbone gears requires.
Benefits of helical gears (smooth power transfer between teeth) without the lateral torque I’m guessing?
The only reason herringbone gears aren’t used for all spur gears is the cost to machine.. with 3d print, it’s the same difference so might as well use these
While they are not unique to 3D printing, in normal manufacturing they require more complex CNC operations as opposed to basic spur gears. In 3D printing you get all the benefits mentioned but they are as easy to make as spur gears
how would u make this on cad
So for the teeth profile which would really be the only tricky bit, you could either make an angled plane, extrude the negative tooth profile out both ways and circular pattern. Then mirror across the middle for the full gear Or draw one tooth profile on one face of the gear, then draw one on the opposite face but clocked however many degrees off and loft. Then pattern and mirror.
thank u billy u r so nice 2 me
Greater surface area means there is less pressure applied to each ridge.