Questions about some words.

The belt is only pulled [in] one side.
Why is it 'in'? Can't it be 'from' or 'on'?

Choose an [accidentally] cross rod.
What does 'accidentally' mean here?

Cut the belt [to] the correct length by cutting another cross rod and remove the [surplus] belt.
What does 'to' mean? Can't it be 'with'?
What does 'surplus' mean? Is it 'excess'?

Check that all sparks and drops of metal are [ground away].
What does 'ground away' here?

Grind off [slump] edges in welds.
What is 'slump' here?

Thank you!