Machining a Cycloidal Drive Gearbox with the Shapeoko Pro

[Nathaniel_Bechard]

This is a long thread detailing the machining of a cycloidal drive gearbox on my Shapeoko Pro XXL.
A cycloidal drive gearbox allows me to achieve a large gear reduction in a small space, and it is machinable on a CNC, since there are no sharp corners, as a planetary gearbox would have.

This gearbox will eventually be used in my rock drill project, more on that later.

My gearbox design has 4 main parts. The cycloid, the housing, the eccentric shaft, and the faceplate (not visible here).

[Nathaniel_Bechard]

I’m starting with two operations to rough out the outer part of the gear. First, and unholy plunge drilling operation, to add a center hole to the stock

Next a contour, using the default carbide 3D settings for aluminum on a Shapeoko.

Machining the stock:

[Nathaniel_Bechard]

Now I’ve got the external features machined.
I’ll then put it in a cycloid gear-shaped cutout for rock-solid work holding during the next few operations. Adaptive toolpaths often exert a lot of torque on the part, so I think this is a better strategy than doing the contour last.

[Nathaniel_Bechard]

Here is my work holding:

The shape is roughed out, then finishing passes are used to bring the shape to the right size.

Next the inner borehole is cut out:

Outer holes are added by drilling (which is probably not a good idea), and then an adaptive roughing toolpath to bring the holes to size.
Once the bearing was popped in, the part looks like this:

[EmGe (Matthew Greig)]

Looking forward to progress!

[Chaotica (Joel McKenzie)]

Love to see this in action as you get it together.

[LiamN (Liam Newcombe)]

Nice,

What material do you plan to make the outer gear from?

[Nathaniel_Bechard]

I’ll be using a chunk of 6061 aluminum. Ideally this whole thing should be made of something more durable than aluminum, but aluminum is the hardest material I can reasonably machine on a shapeoko.

[LiamN (Liam Newcombe)]

Were you planning on having anything between the Aluminium gears as a bearing surface?

[Nathaniel_Bechard]

I decided against that to keep my drive simple. I’m hoping that some grease will make the surfaces slippery enough.

[Nathaniel_Bechard]

I’ve changed the CAD up somewhat. The front area and inside of the gearbox is the same, but the rear has changed somewhat.

Gearing is now present on the back:

.

The bracket on the top holds a bearing. A shaft will come up from it and go to a motor. With the new gearing, the reduction of the gearbox is 40:1

These gears have large teeth, and their root fillet radius is just large enough that I can cut them out with an 1/8th inch cutter.

[Nathaniel_Bechard]

This gearbox will be used for a mini tunnel boring machine. This is why there is a hole in the center of it. The hole allows material to be pulled back from the front using an auger. It also allows for cutting fluid to move forwards.

[Nathaniel_Bechard]

Here is the back of the gearbox with its gear cover:

[Nathaniel_Bechard]

Some progress has been made on the cycloidal reducer body part. Here it is with the first half of the machining done:

This part was a joy to machine.

[Nathaniel_Bechard]

Some cycloidal drive body machining photos:

[Nathaniel_Bechard]

Some work being done on the faceplate of the device:

It’s coming together. The drive is pretty much done

[Nathaniel_Bechard]

I’ve posted the process of making this drive as a youtube video:

https://www.youtube.com/watch?v=thJF_Ol6iEQ

All the manufacturing footage is on there. I would add more clips here, but the file size limit on this forum is too low

[CrookedWoodTex (Tex (Don't Mess With My Texas!))]

Very interesting! What made you decide between the cycloidal drive versus a planetary gear drive; drive ratio?

+1

[Nathaniel_Bechard]

There are a few reasons for my decision:

• I can fully machine a cycloidal drive with a shapeoko. I can’t make the teeth of gears on my machine unless the teeth are very large.
• Since it is for a micro tunnel boring machine, there needs to be a center hole to evacuate material. If I had used a set of planetary gears, my middle gear would have to be at least 50mm across, which would limit my gear ratio and probably make the whole drive wider.