Type of cutter to produce this gear 4

[SchaeflerTom]

Hello All,

I was wondering if I could produce this part with Hob.
Please advise.

Thank you

 

[gearcutter]

The original has been manufactured with a hob as the generating flats are clearly visible in the wash-out area.
Looks like a non-standard profile was used.

Ron Volmershausen
Brunkerville Engineering
Newcastle Australia

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

 

[tbuelna]

That is a rather unusual shape. Due to the undercut and rounded tip profile shown in the cross section, it would likely need to be generated. But the shape of the tips and roots shown in the side view do not appear to match what is shown in the cross section. The teeth in the side view do not appear to have the same undercutting or tip rounding as the teeth shown in the cross section. Maybe it's just an optical illusion.

 

[gearcutter]

tbuelna,
The major diameter is tapered as is the profile or the path of the hob.
This is why the part has that massive undercut and radius in the root but appears to have the correct profile approaching the washout area.
So over the tapered length; the profile's shape changes from minus addendum to plus addendum corrections.
There is no tip rounding.........that's how a profile looks when there is an exaggerated undercut along with a minus addendum correction.

I've no idea why this would be done nor have I ever seen it done before........very strange indeed.

Ron Volmershausen
Brunkerville Engineering
Newcastle Australia

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

 

[mfgenggear]

I would summarize this more of a spline than a gear. taper usually means a snug fit. WAG

 

[SchaeflerTom]

Thanks for all the responses. It's very helpful. This gear is relatively small and about 4mm OD.
It's mated to an internal gear for high speed application where this gear is being driven.
I'm trying to see if I could fix some issues of the original and correct it with a better design.
Undercut is definitely bad on my book. However, the undercut could serve another purpose.
Was it used to reduce the weight of the part which corresponds to mass moment of inertia?
The main objective of the application is high speed and low torque. I think that is why the undercut serves for this purpose.

Thank you.

 

[3DDave]

Unlike most gears, the teeth on this one are supported along one side, so the teeth aren't in simple bending as they would be if the gear was of limited width.

The undercut is usually for clearing the addendum of the mating teeth - is there a picture of the mating gear? Undercut is typical on very small tooth counts.

I just came across this:

http://www.gearotic.com

It's a hobby gear development software by the developer of Mach 3. I guess once you've created the software to drive CNC machines, you want something interesting to do with it.

 

[SchaeflerTom]

this gear will be used to mate with that one at an elevation of certain angle.

Thank you

 

[tbuelna]

SchaeflerTom-

Undercutting of gear flanks is usually something you try to avoid, or at least minimize. While you mentioned this is a gear drive, you did not specify the type of geometry it is based on. From your last post it sounds like this is some sort of bevel gear set, like a straight bevel gear or possibly a face gear. The CAD image of the mating internal gear in your last post is a bit difficult to interpret, so could you provide a shaded iso view? Pinions with very small numbers of teeth (like 8) will usually experience undercutting. The typical approaches used to reduce undercutting are enlarging the pinion, using addendum mods, and increasing the pressure angle. AGMA 1003-G93 annex B table B.1 gives recommendations for an enlarged 8T spur pinion with PA increased to 25deg mating with a much larger external gear. But since your design involves the 8T spur pinion meshing with what appears to be a 31T internal gear(?), modifying the geometry gets a bit more difficult.

Lastly, since you stated this application involves high speeds, you'll want to watch the contact ratio, apply some tip relief to reduce dynamic tooth loading, and do what you can to minimize contact sliding so that the potential for scoring failure is reduced.

 

[mebac]

If you want to do some experiments changing spur gear parameters, try

http://www.me-bac.com.

 

[gearcutter]

That's a neat little app you have there mebac.
Thanks for sharing.

Ron Volmershausen
Brunkerville Engineering
Newcastle Australia

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

 

[SchaeflerTom]

That's an awesome app. I tried it!