Type of cutter to produce this gear
Type of cutter to produce this gear
(OP)
Hello All,
I was wondering if I could produce this part with Hob.
Please advise.
Thank you

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






RE: Type of cutter to produce this gear
Looks like a non-standard profile was used.
Ron Volmershausen
Brunkerville Engineering
Newcastle Australia
http://www.aussieweb.com.au/email.aspx?id=1194181
RE: Type of cutter to produce this gear
RE: Type of cutter to produce this gear
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
RE: Type of cutter to produce this gear
RE: Type of cutter to produce this gear
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.
RE: Type of cutter to produce this gear
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.
RE: Type of cutter to produce this gear
this gear will be used to mate with that one at an elevation of certain angle.
Thank you
RE: Type of cutter to produce this gear
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.
RE: Type of cutter to produce this gear
RE: Type of cutter to produce this gear
Thanks for sharing.
Ron Volmershausen
Brunkerville Engineering
Newcastle Australia
http://www.aussieweb.com.au/email.aspx?id=1194181
RE: Type of cutter to produce this gear