The 3D printer is up and running, although I still have some upgrades waiting in the pipeline. Rather than just printing parts for the printer itself, it is interesting to see if it can be put to other useful work. When a friend heard I was getting a 3D printer, he asked me if I could fix a broken part in his car. The part wasn’t working because a plastic double spur gear had been stripped of its inner teeth:
Could I fix that with the printer? The diameter of the large gear was only 31 mm so quite small! The first thing I did was count the teeth of both the rings, 37 for the large gear and 12 for the little one. I also estimated the “circular pitch” of each gear by measuring with a calliper the diameter on top and bottom of the teeth. The gear heights were also measured.
So now we had some numbers, but creating a duplicate of the gear means we need a computer model representing it. Luckily, there is a great open source program called OpenSCAD and an open source library called MCAD that contains functions for creating 3D involute gears with OpenSCAD. So I used that :
That looks very nice, but is it possible to print it? I tried using 2 different PLA filaments. First, the white top right in the image below, using the familiar eSUN filament. It looks very nice, but I suspect it isn’t quite hard enough for this purpose. Also, it is difficult to get the teeth properly separated.
Therefore, I gave the Printrbot PLA filament a chance (top left below). The calibration boxes I had printed with it seemed quite stiff and hard, so I tried to print the gear with it. The gear that came out was quite promising … all I had to do was manually clean the bore with a 4mm drill bit and very carefully brush up the teeth clearances with a hack saw blade. It gives the impression of being harder than the original gear, so maybe it works. Possibly, ABS would be even better, but I have not come to that stage yet.
The printed gear fits perfectly where the old gear used to be, so maybe it works as a replacement. Now the car owner has 2 spare gears to try out.
These gears were very small, but the test proves that it is certainly possible to print gears of this size or larger. However, it is probably wise to use a slow print speed (I used 20 mm/sec) and possibly even a smaller nozzle than the stock 0.4mm that comes with the Ubis hot end on the Printrbot.
The printed gear from an oblique angle: