$ gpg --expert --gen-key

Your selection? 8

Your selection? s

Your selection? e

Your selection? q

What keysize do you want? (2048) 4096
Key is valid for? (0) 3y
Is this correct? (y/N)y

$ gpg --expert --edit-key john.doe@example.com
gpg> addkey

Your selection? 8
Your selection? e
Your selection? q

What keysize do you want? (2048) 3072
Key is valid for? (0) 6m
Is this correct? (y/N)y
Really create? (y/N) y

gpg> save

$ gpg -a --export-secret-key john.doe@example.com > secret_key
$ gpg -a --gen-revoke john.doe@example.com > revocation_cert.gpg

$ gpg -a --export-secret-subkeys john.doe@example.com > secret_subkeys.gpg
$ gpg --delete-secret-keys john.doe@example.com
Delete this key from the keyring? (y/N) y
This is a secret key! - really delete? (y/N) y
$ gpg --import secret_subkeys.gpg

$ gpg -a --export-secret-keys john.doe@example.com > laptop_keys_secret.gpg
$ gpg -a --export john.doe@example.com > laptop_keys_public.gpg

$ gpg --import laptop_keys_public.gpg
$ gpg --import laptop_keys_secret.gpg