How did the Tin Man meet Dorothy?

Dorothy and the Scarecrow left the cottage in Chapter Five. Dorothy wanted to find water to drink and to wash with, so they walked through the woods until they found a spring. After washing up and drinking her fill, the group decided to make its way back to the yellow brick road, but Dorothy heard a groan nearby. After a short search for the source of the groan..... Dorothy came upon the Tim Man, who was completely motionless and groaning.

Just then another groan reached their ears, and the sound seemed to come from behind them. They turned and walked through the forest a few steps, when Dorothy discovered something shining in a ray of sunshine that fell between the trees. She ran to the place and then stopped short, with a little cry of surprise.
One of the big trees had been partly chopped through, and standing beside it, with an uplifted axe in his hands, was a man made entirely of tin. His head and arms and legs were jointed upon his body, but he stood perfectly motionless, as if he could not stir at all.
Dorothy looked at him in amazement, and so did the Scarecrow, while Toto barked sharply and made a snap at the tin legs, which hurt his teeth.
"Did you groan?" asked Dorothy.
"Yes," answered the tin man, "I did. I've been groaning for more than a year, and no one has ever heard me before or come to help me."