The goal of this step is to form a cross on the bottom layer by correctly placing the four edge pieces around the bottom center. Unlike the other steps of the Fridrich method, the cross is solved almost entirely intuitively. You should try to plan your cross solution in the 15 seconds of inspection given before each solve.
A key fact to understand about the cube is that it consists not of 54 independent stickers, but rather of 8 corners (3 stickers each) and 12 edges (2 stickers each), collectively called cubies. Because stickers always remain on the same cubie, we must not only place the blue stickers on the blue face, but also make sure that each edge cubie is in its correct spot.
Click and drag the applets' background to rotate the cube.
Bad (stickers, not pieces)
For speedcubing, it is equally important to note that we only need to worry about the cross edges' position in relation to one another because we can align them with the middle layer centers at the end using D turns. Our goal is therefore any of the four patterns below. Observe by rotating the cubes that each pattern is off from a completed cross by some number of D turns.
To do this correctly, it is important to know your color scheme by heart. For example, with Japanese color scheme and blue cross, green is opposite yellow, red is opposite orange, and red is to the right of green. The first cross edge to be placed determines the other three's positions.
The simplest way to solve the cross is to place one edge at a time, using the easy moves shown below.
Since each edge takes ~3 moves, in this manner we can expect to complete the cross in ~12 moves. However, the cross can almost always be done in 7 moves. We must consider all four edges for a more efficient solution. The patterns below, involving two adjacent edges, appear often and are extremely useful. Do not try to memorize these; after some practice, the solutions should seem intuitive and even obvious.
Learn to apply these patterns from different directions. For example, you should be able to recognize RB'R2' without first doing y2.
Making the Cross on Bottom
Some fast speedcubers make the cross on top and turn the cube over for F2L. I instead use an approach popularized by Katsuyuki Konishi: make the cross so that it ends up on the bottom. A major advantage of this approach is that it gives us an immediate view of the first two layears, allowing for smooth transitions into F2L, the next step of the Fridrich method. However, it also has these difficulties:
- The color scheme is flipped outside down, making it harder to plan the cross during inspection.
- Because we cannot see the cross, it takes time to realize when we have made a mistake. In the worst case, we might even finish the first two layers before finding a misplaced cross.
- It takes much longer to master than forming the cross on top.
Despite these difficulties, cross on bottom is the best way to reduce the transition time between cross and F2L. We can minimize these disadvantages by starting the cross on another face (frequently L or F) and bring it down to D by the end.
"Looking ahead" aka the most important concept in speedcubing
The transition from cross to F2L is where most Fridrich beginners lose the most time. The solution is to solve the cross at slower than maximum speed. Assuming that we completely memorized the cross during inspection, this allows us to start searching for the first corner-edge pair of F2L as we form the cross. This idea of slowing down and looking for the next pieces is so important that we give it a name: "looking ahead." By reducing the stops between steps and making the solve into one continuous flow, we can significantly reduce the overall solving time. We will revisit this topic in F2L, where looking ahead is the essential technique for achieving a sub-20 average. The top speedcubers are not necessarily those with the fastest fingers, but those who can look ahead the best.
Advanced Cross Techniques
15 seconds of preinspection is a long time to plan out just 4 pieces of the cross and the last move to match the center. Once you are comfortable with the usual cross, keep track of an F2L piece (see F2L), either a corner or an edge, or even the first pair. By planning this out during inspection, we can minimize the delay between the cross and the first pair. As this is where sub-30 cubers often lose the most time, reducing this delay is one of the most important points in getting to sub-20.
One cross technique occasionally used is extended cross, which refers to building the cross and the first F2L pair simultaneously. For a guide with examples of extended cross, see Chris Hardwick's guide. Extended cross is a special case of many possible block openings, which rely on building blocks of cubies that match in color. Some methods that use block openings are Petrus method, Roux method, and Heise method. Although mastering such block openings are much more difficult than the traditional Fridrich cross, being familiar with them allows you to take advantage of special cases you recognize during inspection.
One easy example involves cases where there is already a F2L corner-edge pair in the scramble. If we can solve the cross without destroying this pair, we save a few moves and eliminate any possibility of delay for the first pair.
Examples (Under construction)
Scramble a solved cube with your cross color on bottom: R2 F2 U' R2 L' F2 R' B L2 R B2 R' U B2 U' F2 L B' R2 U' R B R2 L' B'
We can start, for example, by placing the UR piece anywhere on the cross layer. Simple: R'F. This first piece determines the position of the other three: FR edge belongs to DR: R'; DL to DB: LB; finally, FL to DB: DF'. The centers are all matched with the colors of the cross edges, so our cross is completed. R'FR'LBDF' (7 moves). By starting with a different piece, we could have obtained the equally fast solution, FR'FU'F'LFB.
Scramble: D L2 D2 F L D2 R' F L U' D2 R' U2 F U2 L2 U2 R2 B2 U2 L' F2 U' R' D2
Cross Moves: B' R Uw L' D2 F' U F' D
If you've noticed, I did a U in between F' and F' to preserve the corner-edge pair we already had. This way, although the cross became 9 moves, I could go directly into an easy F2L first pair without a moment's hesitation. Always try and look for these little things. You shouldn't go too fast on cross in case you find these.
Scramble: R B' R' U R2 L' D2 U' L' D B' L' U' L R2 B' U2 F' B' U' L2 U' D' L' B2
Cross Moves: F U2 U'w R E2 F D2
What an easy cross.... I could have done DRD2F2 and got the cross in no time. However, always try and use your 15 seconds preinspection time wisely. By doing F and U2 here, we got ourselves 2 corner-edge pair while forming the cross... This is almost too sweet! Like in this example, you can usually wring out something good in 15 seconds. Just don't try to do double extended cross when the chance of messing up is high.
Scramble: R2 F2 U' R2 D F2 U2 B2 U F' D' B L U' F D2 B' F2 U L2
Cross Moves 1: U2F'U2L2R2'FR
Cross Move 2: L2F'RU'F2RFUR2
I see 2 ways to do Extended Cross here.... The reason why you could do Xcross so easily in this case is because you had two 1x1x2 blocks involving 2 blue pieces. This can be extremely useful, and is often times the key to a successful Xcross. Furthermore, in case 1, if you continue UwRUR'U'w for the first pair, you can group the second pair at the same time. (It's not like I read this far during preinspection, but I'm just saying that this is really good.)