GEAR TIP RELIEF TANGENT

[SDETERS]

I need to specify a proper way to dimension a tip relief on a gear. I want the arc I dimension to stay tangent to the involute. If I dimension the tip relief per the attached PDF this will not allow for the radius and the involute to be tangent? How does one specify that a radius needs to stay tangent to an involute segment?

 

[israelkk]

How the gears will be manufactured?

 

[SDETERS]

Good Question looking at a plastic type gear.

 

[tr1ntx]

To get it EXACT, you'll need to construct the involute, then you'll know the endpoint of the involute curve and have your perpendicular. The centerpoint of the tangent arc will be along this line. You'll need to have the involute for the other face of the tooth so you'll have 2 lines that cross to mark center.

I'm assuming you have a computer-generated involute and your CAD won't find a perpendicular. If it will, then draw perpendiculars to the endpoints and show the arc centerpoint. By having an arc centered on a line perpendicular to the endpoint of a curve, that makes it tangent.

Or maybe just call it a fillet between the 2 involutes. That implies tangency, but then you are relying on the maker to get it accurate instead of fudging it.

How accurate does it need to be for plastic gear teeth?

 

[SDETERS]

Cool I will look into this. Only accuracy I need is to keep these arcs involutes all tangent. Thanks for the feedback.

 

[ptruitt]

Am I wrong to assume that one radius is to be tangent to the next one if it just looks as though it is?

Peter Truitt
Minnesota

 

[SDETERS]

That is one of my questions. If the radius is off then the involute is off and there is a disconnect between the two is the part out of print even though both radius and the gear tooth are with in tolerance?

We do not want a ledge, sharp edge or any another type of flaw on these gear teeth. Thanks again for the feedback

 

[gearguru]

If you draw a line from the end of the involute (startpoint of the arc) tangent to the basic circle, then the center of the radius has to be located on that line.
(The length of that line is the local radius of the curvature for your involute in the end point of the involute.)