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).
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:
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.
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:
Looking forward to progress!
Love to see this in action as you get it together.
What material do you plan to make the outer gear from?
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.
Were you planning on having anything between the Aluminium gears as a bearing surface?
I decided against that to keep my drive simple. I’m hoping that some grease will make the surfaces slippery enough.
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.
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.
Here is the back of the gearbox with its gear cover:
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.
Some cycloidal drive body machining photos:
Some work being done on the faceplate of the device:
It’s coming together. The drive is pretty much done
I’ve posted the process of making this drive as a youtube video:
All the manufacturing footage is on there. I would add more clips here, but the file size limit on this forum is too low
Very interesting! What made you decide between the cycloidal drive versus a planetary gear drive; drive ratio?
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.
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