How are Spur Gear Teeth Made Thicker? 2

[TimtheToolMan]

When a pinion spur gear tooth is made thicker to increase bending strength and the mating gear is made thinner, since it is normally stronger, are special cutters needed?

Does it depend on how the gears are cut? Hob, shaper...

One example might be that I want the pinion tooth to be 10% thicker and the gear 10% thinner than normal so they have the same bending strength.

 

[EnglishMuffin]

With the involute tooth form, no special cutters are needed. It's just a matter of making the blank bigger or smaller and radially feeding the cutter in a different amount - less for thicker and more for thinner. Works with hobbing or shaping. Normally referred to as "addendum modification".

 

[TimtheToolMan]

Thanks for the information!

I assume the gear OD then is normally adjusted to keep the tooth height about the same.

Does this mean the pitch diameter is different or considered to be unchanged?

 

[EnglishMuffin]

If you keep the center distance the same, the operating pitch diameters remain the same. If you change the center distance (by thickening one gear more than you thin the other), the operating pitch diameters will change. The operating pitch diameters are both dependent on both gears. The nominal pitch diameters always remain the same however.

 

[TimtheToolMan]

Thanks for the useful information!

 

[eg9arh]

In order to make one toothe thicker and the other thinner you alter the addendum modification. This is generally done by adding the same amount on one tooth as has been removed from the second. The tip dia will change slightly but noit by a significant amount. Addendum modification can most easily be done by moving the hob or cutter in and out of design mesh with the blank. But remeber, the more addendum mod you add, the more spindle like the thinner tooth will become, both the gear and pinion are under equal pitting stress, and at high speed this becomes the dominent load.

 

[TimtheToolMan]

Thanks for the explanation to questions that I have wondered about for sometime.

 

[jbel]

Hey TimTheToolMan,

Is Binford making gears now???