Rob Ives has an excellent instructable on making a laser cut planetary gear, on which this slight remix is based. If you haven't seen it, or his other stuff, go look, I'll wait. Doo dit doo...
Okay, if you made it back or are just forging ahead anyway, when I cut that out on the CO2 laser at our makerspace things meshed but didn't spin as freely as I'd like for a fidget toy. Some scaling up, some scaling down... still no joy. So using the great groundwork he provided, I took a quick trip to the online gear generator at woodgears.ca and created my own ring, sun and planet gears. If you've never done that before fear not - that same site has a great explanation of planetary gear ratios that will make it easy for you.
The other thing I ran into when making Rob's design was I didn't have 5mm dowel of any type lying around. What I did have was a whole ton of not-so-good 3mm ABS and PLA filament for one of the 3d printers. So I changed all the hole sizes so I could use that as the axle instead.
Things you will need:
- The DXF file, and access to a laser cutter (or online cutting service)
- Acrylic sheet, any thickness, approximately 10.5"x6" in size
- About 8" of 3mm ABS or PLA 3D printer filament
- Flush cutters or another tool for cutting the filament
- A nail, some pliers and a way to heat said nail above the melting point of the filament (I used a heat gun)
- A flat surface
- About 5 minutes
Step 1: Cut!
You can use whatever thickness material you happen to have handy - I used both 3mm and 6mm acrylic in the two different examples above. If you're going to cut contrasting color gears just make sure you cut them in the same thickness!
On an 80w CO2 laser and 6mm material (with masking on both sides) the cuts took about 3 minutes. It requires a piece of material approximately 10"x5.5" in size. To check scaling, ensure that the diameter of each of the small holes is exactly 3mm.
Step 2: Assemble!
Cut your 3mm filament into some short pieces, and line everything up - Sun gear in the center, spacer blocks at the top and bottom - then gently tap the filament through the small holes.
Now place the ring gear and the 4 small planetary gears, then put on the cover, aligning it with the other holes and onto the filament 'posts'. Slide it down until the pieces are together, but don't squish them together really hard - the gears should spin very freely.
If the gears don't spin freely you've squashed the pieces together too tightly, loosen them ever so slightly and try again. Worst case you can sand the flat side of the gears to both change their appearance and give a tiny bit more clearance.
Step 3: Rivet, Rivet..
While the whole assembly can be left as-is, it's likely to come apart in this state. Whoops.
What you want to do is slightly melt the ends of one side to form a rivet-like head. Technically you could size the holes to accept plastic pop rivets too, but hey...
In this case I used a nail, held by pliers, and heated it up until it was just hot enough to melt a test piece of filament. Then while hot I gently ran the flat of the nail head over each piece of filament on one side to form a head. Let it cool for a minute or so, then flip it over...
Step 4: Keep on Riveting
With the piece flipped over, push it against a flat surface until the "rivets" on the other side push up against the acrylic. Now trim the filament, leaving just a tiny amount on the front side, heat up your nail (or other tool) and slightly melt the filament on this side, forming more "rivet heads".
Remember to check/adjust the spin of the gears before finalizing this step, and be careful not to touch the acrylic with a hot nail or other item!
Step 5: Fidget
Now spin merrily away!
Thanks to Rob for posting the original design, be sure to check out his other work and happy making!
If you happen to be in the Nashua, NH area, feel free to stop by our makerspace (MakeIt Labs) any Thursday during our open house 6-9, and we'll be happy to show off this, other fun lasery things, and other fun tools.