Printing gears, part I

Gears are an interesting set of things to print. With gears you can make all kinds of things, and if you run an Arduino or a Raspberry Pi, you can significantly extend the toolbox when you can design custom gears. Of course, on Thingiverse, you have literally thousands of gears to pick and print from, but surely you want to make your own?

Blender itself has a Gears add-on, which you can install merely by downloading it and using the Install Add-on feature in the User Preferences. It adds a new type of meshes to the Add Mesh menu, namely Gears. In it you have Gear and Worm Gear, of which I will leave the Worm Gear for later.

When you select Add Mesh – Gears – Gear, you get a default gear looking like this:

Default gear

Default gear

It’s a rather blocky thing, but it would work as it is. But you can edit many features of it: number of teeth, radius, width (ie. thickness), base or the hole in the center, as well as the length of the teeth etc. When you set the number of teeth at 20, radius at 1, width at 0.2, base at 0.75, dedendum at 0.03 and addendum at 0.1 (the amount of tooth that is inside and outside of the radius):

Properties changed

Properties changed

Note, however, that the base hole is still open, and you need to create faces inside it so as to make the object manifold. The easiest way is by using the Bridge feature of LoopTools (another add-on which comes standard, but must be turned on in User Preferences):

Base faces created with Bridge in LoopTools

Base faces created with Bridge in LoopTools

As you can see, the geometry is very clean and nice. You could now just go ahead and create a copy of this, if you wanted a pair of identical ones, then create a base with two axles on it for the gears, and you’d be off in no time. You could also make note of the settings of the gear and create another that has similar teeth but a different number of them. I have not printed this setup, but it would work just fine:

Two identical gears on a block, with axles added

Two identical gears on a block, with axles added

The problem with the Gears add-on is that you need to do some figuring about the base and all other sizes. Therefore I went looking for an alternative methof of making gears and found two.

The first is a website called Woodgears.ca, and it is very easy to use indeed. The site is geared towards woodworkers, who can get templates to cut their wooden gears with, but it works for us printers too.

All you do is design your gear, or two, if you wish, right on the Flash application, and when done, you can either print it as PDF, or, get a screen capture. In either case you should then use a path tracing software, such as Illustrator or the open-source Inkscape to convert it into a Scalable Vector Graphic (SVG) file. That sounds a lot worse than it it actually, but let me show you the screen cap method. Here is the default gear the site opens with:

Gear Template Generator

Gear Template Generator

When we edit the gear a little, it is easy to see that we can now set the size of the axle and all other dimensions really easily. This gear as a shaft of 10 millimeters, which is big enough to print very well. The radius of this gear is  60 mm to the tip of the teeth. If you wish, you can add another gear to the design using the Two Gears checkbox, and even see them animated against each other.

Spokes are another feature that is not available on Blender, so let’s tune this gear up a little. I set the Spokes variable to 3 and Show Spokes is now on.

Three spoke sports edition gear

Three spoke sports edition gear

The grid and the other graphic enhancements are turned on and off with the checkboxes to the lower right. Use them while designing, but don’t leave them on. They will only clutter up the image file that you will trace in Inkscape next. So, turn them off again, and take the last screen dump using the Snipping Tool of Windows. Open the screen dump in Inkscape, and make sure you embed the image – do not link, when asked.

Gear snip in Inkscape

Gear snip in Inkscape

You could merely trace the outline of the design right now, but it would only give you the outline in Blender. Getting a face on the outline is really hard, because this will result in very many curves, so make sure you pur a color, any color, into the gear itself. Use the Paint Bucket tool.

Gear with color

Gear with color

Now we can trace the outlines and then export the resulting SVG file. Select Path – Trace Bitmap, and in the next dialog box, be sure to check “Remove background”, because you only want the gear. The other settings can remain as they are, but if you wish, you can fiddle the settings before the trace, and get a cleaner, less detailed vector graphic out of this. It makes life easier in Blender but is not vital. After you hit OK, you can close the Trace dialog box, and when you take up the Edit Paths tool (F2) you see all the curves that form your gear:

Gear traced into Paths

Gear traced into Paths

The resolution of the gear curves is way past the needs we have for the printer, but let’s not worry about that right now. All that remains in Inkscape is to say Export – Plain SVG, and save the file on your hard drive. Then, open Blender and import the file you just created as SVG. This should look something like this (the gear will be tiny in Blender), when you have selected View Selected and centered the imported object to the grid:

Vectored gear in Blender's Object mode

Vectored gear in Blender’s Object mode

Since this is now a Blender Curve object, you can simply extrude it up to whatever thickness you want.

Extruded gear, still as curve

Extruded gear, still as curve

As you can see from this, it is a very complex Curve object, consisting of thousands of single curves, but when you export to STL, all the detail will be scrubbed. It is a good idea to create the necessary base and axis for this gear before exporting it as STL for printing. In Blender, you can use the Simplify Curves add-on to take some of the complexity off before editing the gear further, but it is not absolutely necessary. The STL export will take care of that.

Single curves shown in object

Single curves shown in object

I won’t print this one either, though I know it would work just fine. The reason is that in Part II, I will introduce you to another tool called the eMachineShop, and I will print the two gears I design with it.

Come to think of it, you can use the Path Tracing method with any gears you find on the Web in images. Just import it into Inkscape and lose the background, then make sure the hear has color, and trace it. I know there are for example PDF files with images (in scale) of all the gears you need to build a clock. Now there’s an idea.

Go on to part II!

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About heikkihietala

Heikki Hietala has worked at the crossroads of IT and language since 1986. He studied at the University of Jyväskylä, Finland. With an M.A. in English Philology and minor degrees in Communication and Information Technology, he has seen action at Microsoft, McKinsey & Company, Lionbridge, Bates Advertising and since September 2003, HAAGA-HELIA University of Applied Sciences. His interests of late have been user interface design and usability, 3D Design using Blender, and information technology for the small and medium enterprises. In his spare time he writes fiction in English. His novel, "Tulagi Hotel", was published in 2010 and a short story collection, "Filtered Light and Other Stories", in 2012. Tulagi Hotel is now available in Kindle and in paperback (also at Akateeminen Kirjakauppa), published by Fingerpress UK. "Hotelli Tulagi" on saatavana myös suomeksi kirjakaupoista kautta maan.
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