Protuberance in gears - Why doesn't shaving operation finish? 1

[namelessudhay]

Just because shaving doesn't finish the root of a gear, a protuberance is given during hobbing. This, most of the time, leads to an undercut. To avoid this, can shaving operation clear root of the gear as well? Thus, I can avoid protuberance.

Another question - Can grinding clear root?

 

[mfgenggear]

Name

Be sure to use an Involute machine to chart the gear teeth flanks. record on charts, use a known tolerance per line on the chart.
such as .0002 tolerance. so that you can visual see the protuberance and measure it. base on the stock it will be an estimated calc.
gear grinding can grind and will remove a step at the root. in my opinion it is better to not cut the root with protuberance. because it is less hassle if it will be ground.
however if it is cut with a hob which will produce a small undercut.it can be ground off. if it is a small enough step to allow removal.

my experience with shavers is limited. but to my under standing, these are my thoughts.
first of all a shaver is not designed to cut the root. however a small undercut of .0015 or less
should clean up. but be advised, it can leave a step. it really depends on your print requirements.
some of my customers allow an under cut or a step.
I prefer a smooth transition. so I prefer grinding, because most of the parts I plan are case harden.
if parts are required or permissible to shave (if hardness is below 45 Hrc approximately) it is an optimal method.

my suggestion here, experiment with the optimal M.O.W. leave more or less stock on the flanks of the teeth.
cut one or two parts then immediately shave it. to verify the flanks clean up. then run production.

A heavy under cut (.0025-.0055) is required when the blue print does not allow grinding of the root after case hardening.
thus an under cut will be present. the difficulty in this type of protuberance it may cut above the true involute but at a gradual reduced step. thus the requirement is that will clean up to the TIF, after grinding. thus it will have a true involute to or below the TIF.
recommendation is the same as shaving hob one or two parts, then grind them, to verify the the results are satisfactory.
other wise the whole lot can be discrepant or even scrap. after gear grinding.

HTH
Mfgenggear

 

[tbuelna]

As noted, most of the time there is no issue with a slight undercut at the flank to fillet transition. The only time this presents a problem is with very high-performance gears. Shaving is a process intended to produce very small adjustments to the flank profile of gear teeth. Rotary shaving cutters are not capable of removing material at their tips, and their tips should never come into contact with root fillet surfaces as this will produce flank profile errors.

If a smooth, continuous, precise profile transition from the flank to the root fillet is required, you can use form grinding to finish the teeth.

 

[namelessudhay]

Thank you both of you. I understand the reason now.