Repair and grinding of capital items

Dear experts,

we are paper manufacturers, and we used to send our paper rolls (capital) for grinding frequently and also grinding/drilling machines for repair.

Is these repair or grinding work are considered as Jobwork ?

if yes,
a) is it require to intimate department before sending for grinding.

b) is it require to file any separate returns apart from gstr1 ?

please guide us.

Thanks in advance.