Labour introducing shifting scale that makes sparks fly (5,4)

'sparks fly' is the definition.
The answer and definition can be both man-made objects as well as being singular nouns.
Maybe there's an association between them I don't understand?

'labour introducing shifting scale' is the wordplay.
'labour' becomes 'toil' (synonyms).
'introducing' is an insertion indicator (some letters introduced or inserted into others).
'shifting' indicates anagramming the letters.
'scale' with letters rearranged gives 'eslac'.
'toil' enclosing 'eslac' is 'TESLA COIL'.

'that makes' is the link.

Can you help me to learn more?