View Full Version : Small gear cutters.

John Stevenson
08-10-2011, 07:29 PM
Art Fenerty of Mach3 and Gearotic fame has brought a new module out for Gearotic.

Because there is a limitation on how small a gear you can cut due the the size of the cutter another way was needed to generate small gears,
As an example for a 32 DP 40 tooth gear, common on small model IC engines you need a 28 thou cutter, if you drop down to 48 DP you need a 19 thou cutter.

Not impossible but probably expensive and time consuming.

The new module adds Tool Wizard in which you specify a round blank and various hocus pocus like cutter used feed rates etc and it mills a flat on the blank, then rotates it 180 and mills a second flat.
It then tilts to a desired angle, 9 degrees is default and the side of the cutter profiles the tooth space.
This 9 degrees will give the necessary clearance for the cutter once hardened.

So basically what you get is a spade bit with two cutting edges.


This isn't one cut with Gearotic but it's similar to what you will get but a bit more accurate than the hand ground one.

You will be able to make the exact cutter you need for the size and tooth count of the gear, no 21 to 25 teeth banding, basically an end mill for every size.

Hope to show some finished blanks later.

P.S. Forgot to mention it's generated not hobbed. :D

08-10-2011, 07:39 PM
Sounds great John....I will keep watching...

and you Sir
How are you making out with all the madness around you..
no damage I hope...
(sorry about the o/t ;)

08-11-2011, 01:42 AM
That looks sweet!
I guess I should find my roto table and a stepper motor and get the rag out.

John Stevenson
08-11-2011, 05:17 AM
Forgot to add that it also generates the profile for timing pulleys as well.


HTD 5 series.


XXL series.

08-11-2011, 10:31 AM
That is really clever. I haven't had a need for small gears (yet) but that looks so intriguing maybe I need to look harder. :D

Thanks for posting about it.

08-11-2011, 10:47 AM
That is the same type cutter that they have been using to make clock gears for hundreds of years,though the old ones were hand filed out.

John Stevenson
08-11-2011, 12:07 PM
Yes George, there is nothing new about the idea, only thing that is new is the machine makes it's own cutter without having to match to a known profile.

Even better if you don't have a profile.

08-11-2011, 01:03 PM
Yes,I understand that. A terrific setup!

08-11-2011, 01:07 PM
Are their any issues with the cutter holding up when cutting a gear with a relatively large number of teeth?

Do you do a single roughing cut followed by a finishing cut or do you nibble it with multiple passes?


Zahnrad Kopf
08-11-2011, 02:33 PM
Yes George, there is nothing new about the idea, only thing that is new is the machine makes it's own cutter without having to match to a known profile. Even better if you don't have a profile.

Hey Old Sod,

Is Gearotic still no charge? if so, this addition makes it a fairly large value to many. (as opposed to just creating the profiling toolpaths).

Well done, to Art and you.

Admittedly, while I have very good CAD and CAM, that woulda been kinda nice while I was cutting 8mm GT2 profiles...



Zahnrad Kopf
08-11-2011, 02:34 PM
P.S. Forgot to mention it's generated not hobbed. :D

That's f'ing awesome. :p :D :rolleyes:

John Stevenson
08-11-2011, 06:02 PM
Gearotic has always been a chargeable program.

No idea on life of the cutter, bearing in mind that for a home made cutter you are limited to silver steel or drill rod unless you can get annealed HSS and the means the harden it.

Main reason this module appears it to allow one to cut the smaller pitch gears that are hard to cut by other means and being smaller tool life should be more reasonable.

However nothing to stop you blocking the tooth space out with a slitting saw first, then just do a clean up pass.

08-11-2011, 08:12 PM
Carbide will cut HSS. Not the best but it will.

Maybe one of those jig grinder attachments and a diamond cutter. Or maybe CBN for steel.

John Stevenson
08-13-2011, 10:14 AM
Here you are Lazlo, one for you.


How about something you can't buy a cutter for ?

Spline tooth, 20/40 DP, 15 teeth.

You get the exact profile, not an approximation based on the closest circle and exact for the size, a 16 tooth spline will be slightly different.

Lazlo, will this fit your Clausing splined cross slide screw ?

08-18-2011, 01:30 PM
Hi John, If possible some details or close-up photos of the cutter geometry in this video would be very interesting.


Thanks in anticipation


08-20-2011, 05:41 PM
Just pushed this to the front to see if I can get some feed-back from John S on post #15


John Stevenson
08-21-2011, 06:45 AM
Sorry missed this.

The cutter in the picture is a single lip cutter, virtually an engraving cutter.

The profile is not correct as the cutter is straight sided and was made for doing a rack. The 'gear' was just an exercise in checked the concept and the code which was a simple hand written sub routine.

The cutter was the only one handy at the time, no idea where it is today, probably been reground into something else so no decent pics.

This is the only one I have of the cutter doing the job it was made for.


Unfortunately it's on the wrong side of the work in this shot.

08-21-2011, 12:14 PM
Thanks for that John, single lip engraving type cutter is as much as I needed to know, although not what I had hoped.