# 7x7x7 last two centers help.

#### TheCuber

##### Member
I've been at these last 2 centers on the 7x7x7 for over 2 hours and I still have not solved them.

I AM GOINGGG CRAZZY. None of the algs from the 5x5x5 are carrying over.

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#### pjk

Staff member
Use commutators for the last piece or so you can't get in. If you don't know how to use them, I'd highly suggest learning, as they come in handy on pretty much any puzzle. I'd suggest reading some of the posts in the How To, Guides, etc. forum, such as Chris Hardwicks 4x4 BLD guide, intro to commutators, Mike Hughey's 4x4 Centers BLD, etc. There are tons of useful posts on this forum, search them out. Good luck.

#### Kenneth

##### Not Alot
This is the general alg: A = any slice, B = any other slice. Do A U B U' A' U B' (just like Niklas) Or A U' B U A' U' B' (mirror the U turns).

#### TheCuber

##### Member
Yup I figured it out. Finally solved my 7x7x7 cube. Now that I know how to solve it, time to record my times.

#### alexgoldberg

##### Member
I don't get to the last couple pieces before solving with comms, do you Pat?

I'll solve the inside rings and as many other pieces I can get with just a couple more simple 3-move swaps. After that I'm all comms, and I solve either 1 piece at a time (1 per face) or two adjacent pieces at a time (only if there are two of the same adjacent pieces within both centers - I haven't looked into doing non-adjacent pieces yet).

What does everybody else do?

##### Member
can i use the 5x5 algs from bigcubes instead if turning 2 layers in R or L turns i turn 3 layers?

#### Leviticus

##### Member
can i use the 5x5 algs from bigcubes instead if turning 2 layers in R or L turns i turn 3 layers?
What algs? For the last 2 edges(In centers)? No you can't. It will scramble the other centers.

##### Member
if it works i would go and get the V-cube 7 if not wait till v-cube 6b is out and buy both tgt

#### mrCage

##### Member
Hi

Hint on using commutators for center solving.

There are basically 2 slightly different ways to do this, but they both follow the P Q P' Q' pattern. The difference lies in that Q can be an outer layer (a face) or an inner layer (a slice).

Basic examples on the 5x5x5 cube (in order to not confuse with non-standardized notation)

1. Q as an outer layer : r' u r - U - r' u' r - U' (written as P-Q-P'-Q')

2. Q as an inner layer: r U2 r' - u - r U2 r' - u' (written as P-Q-P'-Q')

Please also note that a sequence (p1 p2 p3 ...pn) inverted will be
(p1 p2 p3 ...pn)' = pn' p(n-1)' p(n-2)' ... p1'. This is obvious when sitting down with the cube, but easily forgotten when working on paper with notation

Of course cycling blocks can also be done in 2 different ways like described above (if appropriate). Very large blocks may show side effects, due to overlap. Feel free to experiment a bit with this!!

- Per

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#### Leviticus

##### Member
i dont understand a thing O_O

Quote-

http://bigcubes.com/5x5x5/centers.html

Swapping a Single Edge

instead of doing Rr' we do 3R'?

means 3 layer turn.

someone try this.
Where are you getting edges from? I dont think your talking about edges as in center edges, are you?

#### TheCuber

##### Member
What I did was use Leviticus' tutorial on the centers, and than use the following alg for swapping one center piece:

(Rr) U (Rr)' U (Rr) U2 (Rr)'

#### pjk

Staff member
I don't get to the last couple pieces before solving with comms, do you Pat?

I'll solve the inside rings and as many other pieces I can get with just a couple more simple 3-move swaps. After that I'm all comms, and I solve either 1 piece at a time (1 per face) or two adjacent pieces at a time (only if there are two of the same adjacent pieces within both centers - I haven't looked into doing non-adjacent pieces yet).

What does everybody else do?
Hey Alex. I can always get down to 1 or 2 pieces left to swap (on each of the 2 remaining faces), then I use a comm. to do a 3 cycle with those 2 pieces, or 2 comm. to get all 4 pieces solved. I always do my last 2 centers adjacently, and the comm. are pretty easy for the most part. I build all centers by building 1x5 blocks mainly, and it works pretty good I think. There may be a better way to do this, but I want to practice it a lot before I try something else.

#### rjohnson_8ball

##### Member
I downloaded the cube program from GabbaSoft.com and solved the 7x7 a few times over the past couple days. Here is my method of doing the last few center cubies on the final 2 adjacent centers.

Orient the cube so the 2 bad centers are on the F and U faces. Now turn the F and U faces so that if you were to perform an f slice, the bad cubie on the F face would move to where the bad cubie is on the U face. Lets indicate "f" and "r" as the slices that identify the bad cubie on the U face. Now look at this sequence:

U (r f ' r ' f) U ' (f ' r f r ')

The purpose of the initial U is to move the bad cubie on the U face safely out of the way. The (r f ' r ' f) moves the bad cubie on the F face up to the U face where it will want to belong. Next, the U ' puts the bad cubie back into position on the U face. Then (f ' r f r ') brings that bad cubie down to the F face where it belongs.

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#### Mike Hughey

Staff member
Hey Alex. I can always get down to 1 or 2 pieces left to swap (on each of the 2 remaining faces), then I use a comm. to do a 3 cycle with those 2 pieces, or 2 comm. to get all 4 pieces solved. I always do my last 2 centers adjacently, and the comm. are pretty easy for the most part. I build all centers by building 1x5 blocks mainly, and it works pretty good I think. There may be a better way to do this, but I want to practice it a lot before I try something else.
pjk, what is your typical time for centers? I use the exact same method as you, so I'm curious how fast you are with it. It takes me 6 to 8 minutes typically at the moment - way too slow, but I don't know how much of that is my recognition and movement, and how much is the method.

##### Member
i dont understand a thing O_O

Quote-

http://bigcubes.com/5x5x5/centers.html

Swapping a Single Edge

instead of doing Rr' we do 3R'?

means 3 layer turn.

someone try this.
Where are you getting edges from? I dont think your talking about edges as in center edges, are you?

yes i am talking about centre edges

try these.

3R' F' L3' R3 U R3 U' L3 R3'(swaps one centre edge)

and this

R3 U R3' U R3 U2 R3'

where 3 means 3 layers.

ALL gotten from bigcubes(the one i use for my 5x5 method) but i just modified to fit the 7x7.someone try and see if it works.

reference:http://bigcubes.com/5x5x5/centers.html