Crummy iPhone Photo

Here is a screenshot of my CAD program as I was trying to design the drive gear for Mercury. As I mentioned before, the plans I have already have a full scale drawing that I could simply glue to a piece of plywood and I could then just start cutting. I haven’t actually spent that much time on these CAD models though. As I mentioned before, I have a program that created the tooth patterns for them but I noticed the other day that my CAD program will create a gear tooth pattern automatically as well. It allows you to input the number of teeth and the diameter.


It’s worth going into an aside about gears here. The program my friend wrote in C# is actually tailor made for this kind of project in that it lets you input the shaft spacing and the number of teeth; thus dumping out a CAD file in DXF format that you can use directly. If I didn’t want to make cool-looking spokes, I could use those files directly. In all likelihood, my friend will add some code to create spokes automatically. Anybody can create gears like this by going to That is a great website put together by a kindred spirit. He goes into great detail about making gears out of wood and has a flash-based calculator that you can use to make your own. He has recently made an application just like ours that saves the DXF files that you need to feed into the CNC machines. It’s pretty cheap too – I kind of want to buy it just to support him in all his cool projects. If he had made his program available earlier, I certainly would have but my friend is pretty fast with the software – it took him about four days to come up with what we have and he has a day job. If he was unfettered by work, he could probably have done it in a day. I wish I could write software that fast. Anyway, is jammed with awesome projects – everybody should go check it out.

Back to the orrery…

I have all the gears designed (of which there are about 10. A couple of them are actually cage gears which are made from dowels and circles of wood with holes in them. Those are easy compared to real gears.
I also have much of the random spacers and stuff designed but I realized last night that two thicknesses of material are required; therefore, I need to separate these into two CAD files so that we can cut one on the machine, switch out the plywood, and then cut the rest.

By the way, this project calls for several thicknesses of Baltic birch plywood: ½, ¼, and 1/8. For making some quick prototypes to make sure the teeth mesh properly, I’ll just use masonite. Because of the router bit issue I mentioned in my last post, I may have to switch from half inch plywood to one quarter for the largest gears. We’ll see.
If this all works, there’s no reason I couldn’t make another orrery out of plastic or even brass and the beauty of the CNC process is that I won’t have any more work to do. I just go buy the material and put it in the machine. I also will have the future possibility of moving to another machine type such as a laser cutter in the event that my friend kicks me out of his shop because he actually needs to build guitars for a living.

Finally, a word about using a CNC router. I have made many cuts on my bandsaw over the years. No matter how good a job I do while cutting, I always have to clean up the edges by sanding. Everybody has to do that, it’s just part of life when using a band saw. But when you do the same job using a CNC router, the parts come off the machine finished. The edges look perfect and need no further work. It’s really awesome. For that reason and the fact that all these gears and their many teeth would require me to spend hours sanding and filing, I really look forward to using the machine.

This sort of project may become more accessible to a lot of us in the near future. I’m lucky enough to have a good friend with a CNC router and probably very few others have access to that kind of resource but you may soon. There is a place opening up in Tulsa called the Tulsa Fab Lab which is to be a kind of community center for people that like to make stuff. Instead of having a swimming pool and basketball courts, they will have a CNC router, vinyl cutter, laser cutter (for small stuff – not metal or thick wood), etc. Apparently this is a partnership with MIT and I have the impression that there are many more of these in the nascent phase in many cities. The day may soon come where we can all do projects like this. I don’t know – all I know is that I’m starting to build an orrery.

I’m trying to document each step of the fun. Next: cutting some prototype gears to make sure the teeth mesh.