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# Pressure angle for helical gears, with tangential, axial and radial forces.

## Pressure angle for helical gears, with tangential, axial and radial forces.

(OP)
I currenly need to compute tangential, radial and axial forces on a set of gears (metric). The big driven gear is an involute straight teeth gear (spur gear). The driving gear is a small helical gear. The gear ratio is about 20:1. The 2 axis of the gears are not 0 or 90 degrees. It is an odd angle, so the helical gear is so skewed that it resemble a wormgear. I need to compute the forces according to these funny angles.

I found the AGMA standard for involute spur gears (no helical angle). However, the pressure angle is changed by the helical angle in the helical gear. Hence, these equations seems invalid. Is there a standard that describes the geometry of helical gears with the forces equations according to the angles?

Thank you.
Replies continue below

### RE: Pressure angle for helical gears, with tangential, axial and radial forces.

please invest in a gear program that calcs this out. it is complex or seek professional gear designer

### RE: Pressure angle for helical gears, with tangential, axial and radial forces.

I'm pretty sure I know which application you're talking about

The driven spur gear has a simpler shape, so it is perhaps easier to think about things from the perspective of the spur gear.

On the face of the spur gear, there is a contact point (you must find this point). At the contact point, you can say there is a contact plane (which is tangent to the tooth surfaces).

There is a normal force (coincident with the contact point, and normal to the contact plane). This normal force is equal in both gears, but opposite in direction.

Because the helical gear is wiping across the face of the spur gear, there is also a friction force equal to the normal force * friction coefficient. The direction of the friction force is in the same direction as the relative rubbing at the contact point. Again, in accordance with Newton's 3rd law, the friction force is applied equally but oppositely to both parts.

If you know the efficiency of the gearset, then you can estimate the friction coefficient.

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