Cutting Tetrix gears

Yes. For milling gears the set of 8 profile cutters is likely the easiest. I’d have to look but I think my code for cutting gears is only about 5 or 10 lines long. The formulas are easy enough to do by hand. Rolling the formulas into a quick python script allows for the code creation with just a few variables.

Milling gears with the slitting saw is just interesting. For me it’s a novelty. But, it is very similar to what Sandvik is doing with their Invomilling, so it may well be the future. I think this will be a fun project to play with in the fall. A great introduction to 4th axis programming.

We used Gearotic last season to calculate the gear dimension. Looking at it this morning it appears to also support gear milling. I’ll have to play with that some more.

I sorted out the 4th axis at the school last year but I haven’t mounted a chuck or center on it yet. Now that we have a use I’ll have to get cracking on the 4th axis accessories.

If you don’t have a 4th axis, or even if you just have a manual mill you can still cut gears with an indexer. Manual indexers do most counts but are tedious. My Haas indexer is nice because all you do is press a button (or the cnc pulses it).

You can build one using a rotary table and a stepper motor. Here’s an Arduino Sherline Rotary Table controller my friend built.

Last year when I needed to cut a replacement 93 tooth back gear for my Lagun I couldn’t get my Haas to do it correctly, so I made a new control for it. The 7 wire Haas indexers are steppers and super simple to drive. I ended up using Pacific Scientific 6420 stepper indexer and Python with pySerial. Worked perfectly. The URL below also has some images of making many of the gear cutting accessories required.

After all that I discovered the Haas supported circle division but it was a few months after I built my new control. :rolleyes:

It sounds like an interesting read.

I’ve cut a few gears using a hand ground fly cutter also.

Article by Jim Hansen, June/July 2009, Volume 22, Number 3, page 4 also made cover. “Machinist Workshop” magazine uses custom manual indexer plate on Sherline headstock with stock Sherline 5400 turning slitting saw.

Marsh Collins did a long article on building a metal shaper which for me is on page 110 of “Projects 8, The Home Shop Machinist” hardcover. A bigger shaper than the hobby size one from the link provided earlier to Martin Model. It is attractive to me to use just a shaper to make gears because it is very predictable in operation and I make so few. Hobber costs add up.

There are plenty of tips in “Tabletop Machining”:

Page 226 for example they cut a helical gear.

The Sherline 8700 stepper driver rotary table manual has a section on gear cutting.

Now that I scrounged the stuff in grabbing radius ;).

Here is a HSS bar in a fly cutter body using a 4th axis on a desktop mill to make a replacment gear:

Keep in mind if you do that you better be darn sure the fly cutter body is mounted firmly. The link above is a manual indexer but that technique works on a CNC 4th axis as well.

Will update when I get to my library later…

Last fall we downloaded the demo of Gearotic and used it to verify the Tetrix gears we made but didn’t really spend a lot of time using it. I’ve been looking at some of the videos and it does a lot of stuff I didn’t realize it does. You can post 4th axis milling code and cut gears using standard endmills. I think we’ll play with this some more in the fall.

Anyone using Gearotic for milling gears? How about ratchets?


I think this is the current Gearotic website. It has a lot more information.

Looks like a neat piece of software. What are the limitations of the trial version? The website didn’t seem to mention it.

I don’t think you can export or save in demo mode. I tried to post some g-code and got the license notice. Aside from that everything else appears to function.

:cry: so beautiful. Good work!


I re-wrote my python script to handle the gcode creation for using standard profile gear cutters on the 4th axis using just a few variables. My mod 0.8 set of cutters are HSS and 32mm in diameter. The numbering is opposite of B&S cutters. It calculates the blank diameter, whole depth, and recommends the cutter based on tooth count. It also calculates feed and speed based on cutter diameter, tooth count, material SFM, and chip load. It saves the gcode to the local folder using the name given.

Gear Parameters
Module: 0.8
Pressure Angle: 20
Number of Teeth: 104
Gear Width(I): 0.25

Cutter Parameters
Cutter Diameter(mm): 32
Cutter Thickness(mm): 4
Number of Teeth: 12

Feed and Speed
SFM: 280
IPT: 0.001

Blank Diameter: 3.3386
Whole Depth: 0.0713
Cutter Number: 7
RPM: 849
IPM: 10

File Parameters
Enter Filename: tests2.txt

I sorted my back plotter so it renders correctly.

If your interested in hobbing gears rather than milling them… you might want to look at this gem. He started out planning to make a mechanical linkage but instead used an encoder on his spindle with a pulse divider circuit to drive a stepper. It fits on his manual knee mill. The details on photobucket should be enough to duplicate.

Along the same lines Andy Pugh over at Linuxcnc has written a custom hal to pulse divide in a similar fashion. I preferred the divider circuit because it can be fitted to nearly any machine… mill or lathe.