Back for more..VEXpro 2014 Product Unveiling

[Paul Copioli]

Profile Shift, or addendum modification, can be positive or negative. For a positive profile shift, the tooth looks longer and pointier. For a negative profile shift, the tooth looks short and stubby.

The primary use for profile shift in industry is to avoid undercut in small gears. If you want to see severe undercut then look at the 12 tooth CIM pinion. Undercut lowers the gear's max load carrying ability and is necessary so the mating gear's tooth tip does not interfere with the root of the smaller gear.

As a rule, every gear we design will have profile shift to avoid undercut except when the market conditions do not allow it. For example, the 14.5 pressure angle, 20 Diametral Pitch gears that have been used as a standard in FRC have always used 0 profile shift. Making a 12T pinion with 0 profile shift now would mean all of the center distances would be too close together.

This is very important for really small gears with small module (1 or .5). All of our VEX motors used in VRC have significant profile shift to increase the load carrying capability.

All of the Versaplanetary gears have addendum modification to minimize the
planetary backlash and increase the strength as much as possible.


You really are shifting the profile either out (+) or in (-). QTC gears has really great introductory information on their web site about gears. I make all my new engineers read that web site before I give them the more advanced information.

By the way, the 11T pinion is actually stronger in every way than the 12T gear due to the 12T gear's severe undercut. However, the 12T gear's strength is plenty sufficient for use with a CIM motor.

Paul