3D Printing Simple Machines (Wheel and Axle)
Wheel and Axle
Front and Rear Axles on a Car
The wheel has been around for a while, but the addition of an axle adds to the functionality. Imagine two wheels and a long bar attached to a plank, sitting side by side. The wheels by themselves can’t pull the plank.
Attaching them to the center of the plank won’t do any good either - just try rolling it and see what happens! Spoiler: since the two are connected, the plank and wheel will spin together as one, instead of the wheel spinning around the axle. In addition, because the plank is so much bigger than the wheel, it will hit the ground before it’s able to complete a spin. These wheels still can’t drag the plank.
To get real use out of these wheels, you have to put one on either end of the long bar. But that’s not enough - you also have to make it so the wheels can spin around that bar. Otherwise the constrained wheels will spin with the bar and the plank, rolling just until the ground forces a stop, like before. Enter the axle.
Axles run through the center of a wheel, and the wheel can spin around them. For a visual, imagine sticking a pencil through the hole in a CD, and spinning the CD like you’re a disc jockey. THAT is a wheel and axle setup.
If we add a hole in the center of both wheels, making donut shapes out of them, we can put one on either side of the bar. Since the wheels can spin freely, rolling the contraption now will cause the plank to be pulled along with the wheels.
I printed my super-cute wheeled cart. The wheels really spin, exciting! I added some reins then hitched the cart to a ceramic turtle. Scooching the turtle pulled the cart along, wheels spinning. Encouraged, I next hitched a 3-D printed bag clip to the turtle, then tugged it a bit, noting how much the clip seemed to resist being pulled. Lastly I put the clip on the cart, hitched it to the turtle, and tugged again. It moved with noticeably more ease.
According to the AI, there are two reasons a wheeled cart makes moving things easier. One reason is that putting an item on the cart replaces the friction of the item being dragged with the friction of the wheels where they touch ground, so reducing the friction. The other reason is the leverage produced by the difference in size between the axle and the wheel, which lessens the amount of force needed to move a thing.
