The windmill

The key idea

A bishop aiming at the king, a rook in front blocking it, and a king with no squares: every there-and-back of the rook is free material. Start harvesting with the most expensive thing you can reach.

Example 1 · The machine running

The bishop on f6 aims at h8, the rook on g7 blocks its shot, and the black king only has g8. Anything sitting on the seventh rank is doomed.

1. Rxf7+ The windmill starts up, and it starts with the queen. The rook steps off g7, the bishop on f6 fires at h8 — check — and along the way the rook grabs the most expensive piece on the board. Watch the order, it's not arbitrary: as long as the queen stayed on the seventh rank it could come defend g7 and take your machine apart. Whatever threatens your axis, first.
2. Kg8 Only square. h7 is taken away by the rook from f7 and f8 is occupied by its own knight — which is exactly what a windmill needs: a king with a single exit.
3. Rg7+ The rook comes back to its post with check, and it's defended by the bishop, so the king can't take it. This is the axis of the windmill: the rook pivots on g7, goes out to harvest and comes back.
4. Kh8 The king goes back to the corner, forced, and the machine is loaded again. Black is watching the whole film and can't change the ending.
5. Rxd7+ Second round: the rook goes out along the seventh, grabs the d7 pawn and the bishop delivers the check. One piece per round. Nobody has had to calculate anything complicated — you just have to see the mechanism.
6. Kg8 Back to g8. There are no more squares and there aren't going to be any.
7. Rg7+ Back to the axis with check. Third loading of the machine.
8. Kh8 And the king, back to the corner.
9. Rxb7 Third pawn, and the rook is already at the other end of the board without having taken a single risk. ALWAYS calculate the full route before starting: what decides the game usually isn't the first capture, it's how far the rook reaches.
10. Kg8 The king steps aside for the umpteenth time. Tally of the operation: a queen and two pawns, without giving the rival a single turn to think.
11. Rg7+ And the machine is still standing, ready for another round. Whenever you see a bishop and a rook lined up against a boxed-in king, stop and count: there's almost always more than it looks like.

Example 2 · How it gets built: the price of entry

Here the windmill doesn't exist yet: it has to be built. And the material it costs to build gets recovered on the very first round.

1. Rxg7+ The whole rook for a pawn. It's not a hunch: the bishop on b2 is already aiming at h8 along the long diagonal, and all the windmill is missing is a rook on g7. This isn't giving away the rook — it's installing it. And the king can't take it: the bishop defends it.
2. Kh8 Only legal square. Kxg7 is illegal because the bishop defends it, f8 is blocked by its own knight… and the king walks right into the corner where the machine grinds it up.
3. Rxf7+ First round: the rook leaves g7, the bishop fires at h8 and the f7 pawn falls along the way. This is where you find out whether the sacrifice was calculated right — the material starts coming back next move, not ten moves down the line.
4. Kg8 Back to g8, half of its cell.
5. Rg7+ The rook returns to the axis with check, defended by the bishop again. The machine is running on its own now.
6. Kh8 And the king, to the other half of its cell.
7. Rxd7+ Second harvest. Notice the rook is clearing the seventh rank from right to left: every pawn it takes clears the way to reach further on the next round.
8. Kg8 The pendulum, unshaken.
9. Rg7+ Check and back to the axis. Third loading… and this is the good one.
10. Kh8 Corner, for the last time.
11. Rg3# Mate. And look at WHY it's mate: the rook comes down the g-file, so the bishop gives check and g8 is forbidden; h7 is blocked by its own pawn; and there's nobody on the diagonal who can block it. That's the real ending of the windmill — not the material count, but a king that's spent ten moves unable to leave two squares. Before giving up the rook, calculate this far.

Practice

The machine is built: bishop on f6 aiming at h8, rook on g7 blocking its shot, and a black king with only one square. Set it running — and start with whatever bothers you most.

1. First round, straight for the queen: it was the only piece that could come defend g7 and break your axis. Move the rook off g7 so the bishop can fire… and do it along the seventh rank, grabbing the most expensive thing within reach.
2. Back to the axis with check, defended by the bishop: the king can't touch it. The machine is reloaded. Return the rook to g7. It's check, and the bishop protects it.
3. Second harvest. Same mechanism, same forced reply from the king. Repeat the usual move: the rook goes out along the seventh rank taking, and the bishop delivers check.
4. And back to the axis again. Now it's just a matter of collecting the expensive stuff. Rook back to g7 with check.
5. All the way to the other end of the board. Three rounds of the windmill: a queen and two pawns, and the rival hasn't played a single move of their own the whole sequence. Last trip along the seventh rank, and this time all the way: see what's left on b7.

The windmill, built and carried out by you. Remember the picture: bishop aiming at the king, rook in front blocking it, king with a single square. When you see it in your own games — for you or against you — you'll know it's not just any position: it's a material grinder.