Asking how the saw is made to be friendly or friend-like is an interesting question, considering that the first line doesn't make the saw sound nice at all. The saw snarls and rattles in the first line of the poem, yet within a few lines of that, the saw is definitely softened a bit:
And made dust and dropped stove-length sticks of wood,
Sweet-scented stuff when the breeze drew across it.
The saw produces a product that smells wonderful. The sawdust smells sweet, and that should be a familiar good smell to many readers. Freshly cut wood smells great, so it makes sense that the boy loves working with a tool that allows him to smell that particular scent. The other part of the poem that seems to indicate the saw in a friendly nature comes when the saw seems to leap at the call for supper.
As if to prove saws knew what supper meant,
Leaped out at the boy’s hand, or seemed to leap—
"Leap" is a happy-sounding word in general. I know what the text is indicating. Occasionally, a saw will bind or bite in the wood, and the saw and/or wood will jerk or jump. It can be dangerous for the operator, and it is never a good thing. That's why it's odd that the narrator chooses the leaping image. A friend would leap for joy with the boy, and that is what the line seems to indicate; however, within a few lines, we learn that the saw's leap caused the boy great trauma. The other thing to notice is that the saw is made to be a living entity that can do things like leap. A tool is an inanimate object that a user manipulates—it can perform no action without a user. Yet in this poem the saw is presented as a helper for the boy. It's not an enemy preventing him from doing his work; it's a friend helping him do a man's work.