Making a Laser Cut Planetary Gear





Introduction: Making a Laser Cut Planetary Gear

This project is originally from here.
You can visit for a chance to win a ready made version of this planetary gear mechanism

This tactile and delightful looking mechanism is a planetary gear. So named for the four planet gears orbiting the central sun gear. I've put this project together as part of my learning-to-use-a-laser-cutter experiments.
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Step 1:

The parts are all laid out in a pdf file and then transferred to the Laser Cutter software. The downloadable file is available as a link in the previous step. I've left it as a pdf file as, if you have, or have access to, a laser cutter then you will know how best to convert it for use on your particular machine.

Step 2:

Even if you don't have your own laser cutter you may well be able to find one that you can use in your local area, perhaps in a FabLab or a Hacker Space. These type of resources are popping up all over the place so it is well worth checking to see if there is one in your area.
I've cut the parts out from 3mm acrylic sheet. (Perspex) I also used a length of 6mm diameter acrylic rod to hold everything together. There is no glue in this model. All the circular holes in the model should be a tight fit. It might be worth shrinking down the size of the circular holes to, say, 5.6mm. Try cutting one circular hole and making sure that it is a tight fit with the perspex rod before you cut out all your parts.

Step 3:

Cut five 9mm long lengths from the 6mm rod. I've used a junior hacksaw. There must be a better way! Let me know if you know of a proper tool for the job.

Step 4:

Here are all the parts laid out ready for assembly. I used a different colour of perspex for the planet gears so that they stand out in the finished model.

Step 5:

Fit the five pegs into the five holes of the back plate. A hammer can be handy at this point if the pegs are a really tight fit.
Tap the centre gear onto the centre peg. This gear is fixed, it should not be free to rotate.

Step 6:

Fit the two end caps into place and tap them down.

Step 7:

Drop the large ring gear (the annulus) into place between the two end stops. Space the four planetary gears around the central gear.

Step 8:

Finish off the gear by tapping the top plate into position. Turn the annulus gear and watch the planet gears rotating!

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Very nice, I'd like to live on the third planet from the sun, I like it hot. That's why I live in southern Arizona. :o)

Very nice project. Use the laser to cut Perspex rod! The type of laser may influence the exact method but it makes a smooth, clear, and exactly perpendicular cut. I am not familiar with laser rental rates but actual laser time to make each cut of an acrylic rod is no more than a few seconds. I am fortunate to be able to use rods up to 8' long but if the laser you use handles smaller sizes you can cut them to a length that fits with whatever saw you have available without worrying about how accurate that cut is. The first laser cut is made as close to one end as possible. That cleans up that end and establishes a known baseline from which to cut exact lengths. An allowance can be made for the laser kerf if that level of precision is required, but a few thousandths is negligible for most applications.

4 replies

thanks for the tip! I tried laser cutting but it ends up with a shaft end that is slightly angled, as if the cut had a 'v' shaped section. Any tips? I did think about trying cutting with multiple passes...

Hey robives...sorry for leaving out important information. I’ve been working with lasers long enough that setup parameters for different materials are usually performed with my mind on a walkabout so I sometimes overlook them when trying to pass on information to someone else.
The issue causing your non-perpendicular cut is primarily the focal length of the optics used by the laser weapon of your choice. The majority of CO2 lasers (typically centered around 10.6 micron wavelength) use a system of mirrors to direct the beam. The rest, such as mine, eliminate all the mirrors and either move the laser over the material or, maneuver the material underneath a stationary laser. Naturally there are variations and/or combinations of these and other laser subsystems to keep it entertaining. Either way, the final element of the beam path prior to impacting the material is the optics system. The beam is focused as it passes through those optical element(s).
It is this optics assembly, or focal tube, that causes your cuts to be v-shaped rather than a smooth perpendicular line. Every focal tube is designed to focus the power density of the beam at a specific distance from the exit point of the tube. The shape of the beam after passing through the optics is much like an hourglass. The maximum power location of the beam corresponds to the constriction point at the center of the hourglass. Power density falls off gradually on both sides of that point (above and below) and would be plotted out in that hourglass shape if you had the data points from testing available. In a similar way that hourglasses can be short and wide or tall and skinny, the design of the optics in a given focal tube can be used to dictate, up to a point, whether the useful power of the beam is spread over a longer distance (cuts thicker material for example) or is focused fairly tightly around the specific focal point (e.g. this may be necessary to provide enough power to cut through thinner materials that do not as easily absorb the 10.6 micron wavelength beam).

I hope that gives you a reasonable idea of where this winds up. So far as I am aware all lasers have removable focal tubes; the optics must be cleaned regularly or any foreign material on the lens system will definitely reduce the power delivered to the target and potentially could cause serious damage to the laser and/or the material being lased, mostly through heat buildup. Because they are removable they are also typically available in different focal lengths. Which brings us to your v-notch. Check with whoever owns the laser you use to see if they have optics available with a different focal length that will provide a (virtually) straight cut through 6mm acrylic. Unfortunately, I can’t tell you what focal length to ask for because my open gantry 54” x 102” system uses an entirely different beam shaping system than cabinet lasers, but your laser guy should know what you need for his equipment to provide the cut you need. I hope you were able to understand the issue in spite of my poor communications skills and I also hope you are able to use the necessary optics in a cost effective way. Best luck!

Thanks for that laserlad - very useful information!

The laser does cut with a V shape section. I suppose you could cut these things with a rotary attachment but you'd end up with a point in the middle of the rod where the V cuts from all sides.

You have access to a laser cutter and scrap acrylic, why don't you make your own miter box?

1 reply

Excellent idea!

awsome build, this makes me wonder though, What progrma did you use in order to make the shapes as complex as the gears?

Cutting the dowel pegs can be easily done with the laser. Make a jig, lay the stock on the jig and make the cuts. I have an Epilog 35w unit... I was making puzzle pieces from 1/2 inch stock. I think I have a YouTube video showing the process using wood for the prototype... then I did the plastic ones.

Found them...





You don't need anything that elaborate... a slot laser cut into wood or plastic, lay the length of dowel in, then have it make the horizontal cuts... nice and smooth.

This has some wonderful possibilities. These can be handed out in trade-shows either in kit form or assembled, depending on the trade show. A business card or QR code with business info could be etched on the back. Very memorable and gives you something to do when you are waiting for the computer to download several gigabytes. ;)

This would make a rather good base for a Magic the Gathering life counter...

very beautiful

I love planetary gears! If I might make a suggestion: when you are cutting that rod with a saw, 1) get a finer micro saw like for models, Xacto sells them, and 2) make a mitre box-like implement (think of a bagel slicer). Doing it by hand on a vice is asking for uneven cuts.

1 reply

Thanks! I've ordered an xacto mitre box and saw.

the time of the "on demand production" is here...
we must find ways to use it "for real"...