Tip break: chamfer, round, deburr, or nothing?

[geesamand]

I'm trying to understand the pros and cons of these choices for the edge between the EAP and outer diameter of the gear. My vendors seem to call this the "tip break".

Assuming the gear profile has tip (and root) relief, it seems like the only value to the shape of this edge is precaution against handling damage and chipping and has no effect on rating. Is this true?

David

 

[tbuelna]

geesamand,

If your gears are case hardened the tooth edge breaks are fairly important. A careful tip edge break prior to case hardening helps to produce a case thickness with no abrupt transitions. And it also prevents through hardening of the edges, which would lead to brittleness and cracking. Otherwise, as long as you use proper tip relief, this surface is not subject to contact. So it would not likely have an effect on rating.

But since the actual distance from the OD to EAP is usually quite small on most gears, the tip break dimensions must be carefully controlled. In fact, for this reason there are now CNC machines designed specifically for producing gear tooth edge breaks.

http://www.fimat-srl.it/eng/deburring_machines_for_gears.pdf

Hope that helps.
Terry

 

[geesamand]

Yes, C&G in 8620, 4140, etc. Knock on wood I've yet to seen embrittlement damage.

I've seen a variety come through and I'm personally partial to the chamfer performed prior to hardening (ramped hob) as this is better protection against handling damage. But another option is a thousandth or so radius done at grinding. I've seen it arrive in all ways from our vendors so the real question is what method is most sensible for us.

 

[gearcutter]

As Terry mentioned;
Tip chamfering (along with tip & root relief) if not applied correctly will decrease the contact ratio thereby de-rating the set slightly.
Be careful how much you apply.

Tip chamfering (or rounding) will also aid with oil entrapment.

Ron Volmershausen
Brunkerville Engineering
Newcastle Australia

http://www.aussieweb.com.au/email.aspx?id=1194181