Cubes pop. The pieces are held together only by their shape, so a hard turn while another layer is not lined up, or a drop onto a hard floor, can push one out. The cube is not broken, and the piece goes back in with your fingers.
What matters is which way round it goes back, because that decides whether the cube can still be solved. Here is how to get that right.
An edge piece can sit in its slot two ways and a corner three ways, and only one of them is right. Push it in the wrong way and the cube still turns perfectly well, but it will stop one piece short at the very end.
Easy: turn the piece until each of its colours matches the stickers beside it on the same face, then push it in.
There is no way to tell by looking, so put it in whichever way looks best and solve as normal. If you reach the end with one corner twisted or one edge backwards, that is the piece, and the repair guide shows how to put it right in a minute. Or scan the cube with Way of Cube first, and it will tell you straight away whether the piece went in the wrong way round.
An edge is the kind of piece with two colours. They pop most often, and they are the easiest to put back.
A corner has three colours. Corners pop less often and are stiffer to push back, so this is a good job for a grown-up's hands.
If a corner keeps refusing, pop the edge next to the gap out first, put the corner in, then put the edge back. Two easy pieces are kinder than one forced one.
On most cubes the six centres stay fixed to the middle, so the cube can always be built back up around them. The trick is to build it back solved, not in whatever order the pieces come to hand.
A cube pushed back together at random can be solved only one time in twelve. A corner can go in three ways, an edge two, and two pieces can be swapped, and only one combination of all three is a cube that turning can finish.
A cube that pops again and again is usually set too loose. Many cubes, especially speed cubes, have a screw or a dial under each centre cap that sets how tight the layers are. Turning each one a little tighter, all six by the same amount, stops the popping. Some toy-shop cubes are sealed and cannot be adjusted, and the box or the maker's instructions will say which kind you have.
A stiff cube is tiring for small hands and pops when it is forced. A drop or two of silicone lubricant made for puzzle cubes, worked in by turning every side for a minute, makes a big difference. Do not use cooking oil, WD-40 or anything petroleum based: those can make the plastic sticky or crack it over time.
A cube that looks bent is often just a layer knocked out of line, and turning each layer back until it is square fixes that. If the plastic itself has bent, usually from heat such as a hot car, a dishwasher or a radiator, the cube will keep catching and popping however it is adjusted. Cracked pieces are the same. Then it is time for a new cube.
Popped pieces are small. If there is a toddler in the house, gather them up straight away.
Once the pieces are back in, Way of Cube can check the cube for you. Show it the six sides through the camera. If a piece went back the wrong way round, it lights up that piece and shows which way to turn or flip it. If everything is right, it teaches the solve from exactly where your cube is.
Free, no account, and the camera pictures never leave your device.
Turn the top layer about half way between two positions so an edge sticks out, then lever that edge up from underneath with a thumb or the handle end of a teaspoon. It comes out with a pop. Edges always come out first; once one is out, the corners next to it can be eased out too.
Yes, as long as the piece goes back in the same spot the right way round. If it went in the wrong way, the cube will stop one piece short at the end, and that piece can be twisted or flipped back by hand.
Usually not. It is most often set too loose, or being turned hard while a layer is not lined up. Tightening it, where the cube allows, and keeping each layer square before turning the next both help. A cracked or heat-bent piece is the one thing that really does mean a new cube.
Silicone lubricant made for puzzle cubes, a drop or two at a time. Avoid cooking oil, WD-40 and petroleum-based products, which can damage the plastic.