Problem in Internal gear shaping

[gearman1234]

We have to shape 8/10 DP, 25 Deg, 4.8 ID, 5.313 Maj Dia , 40 Teeth Internal gear.This gear is being shaped on TOS OHA 50B gear shaper. It is observed that the shaper cutter is getting rubbed on the trailing edge clearance face. After checking all possible reasons, we have zeroed in on one reason. During the return stroke the cutter should retract obliquely at a set retarction angle. The sense of rotation of cutter during retraction should be the same as that of the internal gear or cutter(since both have same sense of rotation in internal shaping)

But actually the sense of cutter rotation during retarction is opposite to that of gear/cutter rotation, thereby causing the interfernce of trailing edge with the gear tooth flank.

What is the solution to this problem? Is it related to software or a mechanical problem?

 

[diamondjim]

How many teeth are in the cutter?
Are you certain that the cutter does
not have play in it? Reach up and see
if it has circumferential play.

 

[gearguru]

gearman1234,
Don't you have the problem with the interference between the tips of the teeth, as described in Dudley's "Handbook of Practical Gear Design", Chapter 3.11 Pg. 3.34 and 3.35 (and in many other gear design handbooks)? Some internal gear/pinion combinations can NOT be assembled radially, only axially. The same problem can occure if the cutting tool is shaped as a pinion. Your problem needs to be evaluated with the complete tool and gear dimensional data.
gearguru

 

[diamondjim]

I think gearguru is probably right and
that is why I was asking for particulars
on the cutter i.e. number or teeth etc.
Fouling is the term for this condition
and has been explained moderately in some
text books as the geometry involved is
quite complex or time consuming. With
Computers this is not so great a task,
but still needs to be programmed. I have
not seen a computer program that will check
this condition and may have to be written
after having checks made along the line
of action and calculating the relative
points of the cutter and gear thru many
of the rotations of the cutter and part
as they are generated. The number of teeth
of the cutter and gear are the important
factors as well as the profile shift to
cut backlash or cut a profile shift. An old
rule of thumb is the cutter must have at
least 24 teeth less or have special addendum
and tooth thickness to generate the parts.

 

[smah]

gearman1234, it is not a software problem exactly and it's not a mechanical problem exaclty. It is really a geometry problem. I don't know this machine, so I can't give specifics. What you're seeing is commonly called trailing side rub. Some of the contributing factors are gear geometry, cutter geometry (including life posistion aka amount of sharpening), machine backoff angle (retraction angle), and backoff amount (retraction amount). In general, some thing that can be done to help this condition are:

change backoff angle closer to 0° - maybe even beyond
reduce backoff amount
use a newer cutter (less grind back)

You will have to experiment to find the best conditions. Not all of the above changes may be practical - for example, if the backoff amount is controlled by a mechanical cam, this may too costly or time consuming to change.