Assembled gears

Posted on November 4, 2017

This week was one when I was busy with fabricating and assembling pieces.

Bushing and Peg Designs

In order for the second gear to hold into the prototype, and to turn freely when the motor gear turns, a bushing is needed. Looking at the side cut figure of the prototype, the string will pull on the peg, putting pressure on the wood of the piece. By creating a bushing with a bottom flange, the tension will be distributed in a wider area, reducing risk of enlarging the bushing hole. In my sketch above, I planned to have some pointy tips bent so that the bushing would dig into the wood.

Once the bushing part is solved, I had to design the peg that will go through the piece, and onto which the second gear and the string will be attached. In the sketches above, you can see notches, as I still was planning to use C-Clips.

A metal shop technician suggested that I used the lathe to prepare the bushing. This got me thinking: instead of using a washer at the bottom, held by a C-Clip, I should lathe the peg so it has a bottom flange, integrated with the peg.

Instead of using a C-Clip above the wood, I thought to drill a hole and use a cotter pin to prevent the peg from falling into the prototype body. I could have used that kind of pin at the bottom of the peg as well, however there would be a risk of the turning pin would get caught in the electronics’ wires. Best to avoid that. Above the body, there is no such risk, since the pin would turn at the same pace as the gear.

Lathing

After carefully designing the components, I was able to spend a morning with a technician at the metal shop on the lathe. From a 1″ thick rod of steel, we shaved of some metal and drilled a hole in the piece. We also cut the peg in the same manner.

There is something quite impressive in drawing something and then making it come to life.

Assembling the Piece

After the bushing was made, I spent some time cutting it and hammering it to create its pointy parts. The piece didn’t look as pretty as my drawing, which saddened me a bit. Speaking with the wood shop technician, he told me that it would have been better if I hadn’t bent it, and just planned to enter it tightly into the wood.

Well, too late now.

So I placed the bushing inside the prototype, then passed the peg through.

As you can see from the video above, it worked perfectly!

The wooden noise comes from two things. First, the stepper motor’s movement is kicking the second gear forward and its teeth knocks against the small gear’s teeth. Also, the peg is wiggling a bit.

Finally, I could add the string, which also makes the peg more steady.

Since the big gear is only forced onto the peg, but is not physically attached to the peg. As visible in the video above, it rotates while the peg remains in place.

In order to fix this, I will pass a pin through the big gear and see if that works. At this point, either all will work as expected, or the big gear will break. To be continued.