What is Tip relief radius in Gear data 1

[samsangsam]

Receive a First acticle inspection for a molding gear, drawing mention in gear data about Tip relief radius , supplier don't what is it , either i.

What is Tip relief radius in Gear data? How to measure this ?

 

[MikeHalloran]

http://en.wikipedia.org/wiki/List_of_gear_nomenclature#Tip_relief

On an external gear, it's an external radius, where the tooth is thinned below the theoretical involute profile, outboard of the pitch circle.

I think it's commonly measured with templates, either directly on the gear, or on a profile projector if the gear is small.

More reading here:

https://www.google.com/search?q=tip...s=org.mozilla:en-US:official&client=firefox-a

Mike Halloran
Pembroke Pines, FL, USA

 

[tbuelna]

With most gear tooth profiles, there is usually a tip corner max/min radius limit specified. And with high-performance gear tooth profiles, there are limits specified for a tip relief that deviates from the involute profile. The tip relief prevents excessive dynamic contact loads as the approaching gear teeth initially mesh.

The shape of a tip relief is not a simple radius profile. It is a curvature that smoothly blends the active involute profile to the tip radius. Most tip reliefs only deviate a few thousandths of an inch from the involute profile over the last 2 or 3 percent of the tooth flank.

The tip relief can be measured with a CMM.

 

[samsangsam]

how the CMM can be measure? the gear data table have no tolerance , only specify a value ..

 

[MikeHalloran]

Your CMM operator will be faced with tracing the gear profile, figuring out where the involute ends and the radius begins (difficult because they're intentionally blended), measuring the radius, and verifying that it is or is not as specified within the default tolerance.

... illustrating another way in which CMMs can waste incredible amounts of time.


Mike Halloran
Pembroke Pines, FL, USA

 

[tbuelna]

A few years back, the involute profile and allowable tolerance deviation was defined using what was called a "K" chart. The K chart defined specific points on the flank profile such as start/end of active profile, start of tip relief, start of corner break, high/low point of single tooth contact, etc. Now days things are more complicated, since the profile data must be more explicitly defined, including the characteristics of the profile curve such as slope, concavity/convexity, etc.

 

[geesamand]

The way I see this is: you can't apply it as part of a K-chart. A radius is a radius. A K-chart requires explicit points in the (diameter, (offset from pure involute)) coordinate frame. Surely it can be done but it's entirely not obvious.

I would interpret it as a true radius on the tooth tip between the involute face and the outer diameter. Does the specified radius agree with the nominal size of the top lands?

David

 

[tbuelna]

Attached is a sample drawing of a molded plastic helical spur gear. In the "tooth proportions" table there is a requirement for "normal tip radius", which is a tip break and not a tip relief.

 

[geesamand]

To that point: I have been in situations where one company's tip relief was another company's tip break. To me, tip relief is profile relief on the addendum side of the profile. Tip break is the treatment of the edge between the active face and top land. I have seen others mix the terms.

What I described previously is a tip break in the form of a radius. (Other tip breaks are chamfers) Not all drawings are as clear on their terminology.

David

 

[tbuelna]

The OP asked about a molded (plastic?) gear. A molded plastic gear presents some differences to a machined gear in regards to the tip break. The tip break profile of a molded plastic gear is created by the mold surface, while the tip break of a machined gear is created by a machining or hand working operation after the tooth flanks are cut. The attachment provides a brief description of how tip breaks are defined with a molded gear.