January 2011


I stopped on my way home last night to buy some pine for my orrery base and top. I jointed the edges and glued it up too. Then I held the drawing up to the panel and realized that it’s about one inch too narrow.

Doh!

So much for eyeballing measurements. I should really read the directions more. On the plus side, I cut some other materials to size like shafts and whatnot although I’m a bit afraid to check them against the drawings.

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SaturnI remembered that Saturn needed rings.  This wasn’t too hard.  I went to the almighty internets and quickly found a photo from one of the space probes that featured a nice almost-top view of Saturn and it’s rings.  I took this and used photoshop to round-ify it since it was a bit squished due to the perspective of the space probe.  I printed it out and stuck it to a piece of stiff plastic (in fact it was the license plate from the front of Melissa’s new car that advertised the car lot).  That plastic source wasn’t the best idea – it’s extremely tough to cut with anything.  Anyway, the photo shows the final product.

The photo shows, if anything, too much detail.  I may redo the rings since they look a bit rough.  But not today.

And Erin is officially in the musical. She’s in the chorus which where she wanted to be.

Well, today I went over to my friend’s house and we played
CNC for a few hours. CNC Prep The first image is of the router hovering over the
piece of 1/8″ Masonite I brought over for the tests. This is
just before the router lowers itself down until it touches that
piece of metal right under the bit. In this way, it learns
where the material starts (minus the thickness of the metal plate
that is). Freshly Milled

This next image is right after the router has cut
the gears and moved off so we can pop them out. We forgot to
leave a little tab of wood there so that as the piece is cut out
the bit doesn’t grab it and throw it in some random
direction. That actually happened to a couple of the spoke
cutouts. Next time, we’ll remember that. That brush
looking thing is in fact a brush that surrounds the bit while
cutting and serves to keep the sawdust from going everywhere; the
dust collector sucks it all out the top. The finished prototypes

Finally this photo shows the prototypes.
They’re a bit fuzzy around the edges when they come off the router
but a quick touch with sandpaper gets all that off and the result
is near perfect. As you can see they mesh pretty well. I
bought a 1/16 router bit on the way over and as was walking around
with it in my hand, I dropped it and naturally the bit hit the
concrete and snapped right off. So $15 down the toilet.
We had to use a 1/8 bit that he already had and as a result, the
bottoms of the gear teeth are much rounder than the CAD model but
it seems not to matter. I guess it would if we were trying to
build a transmission that will carry a load like for a car but this
is just for a small desktop orrery. I think this will work
fine. Also, I forgot to put all my models but this on my
memory stick or we could have cut a whole bunch. No matter;
everything worked as well as I could have hoped. I also
bought most of the material I’ll need on Saturday so hopefully soon
I can cut some ‘real’ parts and get started putting the thing
together.

Six Potential PlanetsHere is my first set of six planets.  I’ll consider painting some on the next orrery if I ever build one.  These don’t look too bad with a bit of stain on them.  Here you see them perched on some pieces of wire stuck into a scrap of plywood to dry.  After this photo was made I put a coat of shellac on them to boost the shininess.  I’m pretty happy with them.  On to the gear prototyping!

Wooden candidates for planets

Here are some wooden balls I bought to make the planets with. I only bought three sizes since that’s what hobby lobby had. The plans mention rolling them out of clay but this is woodworking! They need to be made of wood. If I had more initiative, I’d get some chunks of various species and turn them on a lathe but for now, these will do.

 

A couple of them have some noticeable grain so those might make passable facsimiles for Jupiter and Saturn with a little stain on them.

I’m trying to get over to my friend’s house tomorrow to cut some gear prototypes but he’s pretty busy – he’s volunteered to mentor the local high school robotics team and it’s robot season.

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 www.woodgears.ca. 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, woodgears.ca 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.

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