12-11-2017, 02:37 PM
If put the head on as a guide spot the end of the stud with the largest drill that will go down the hole.This will give you a centre.then drill down through with say a 5 mm drill ,if you have a helper get them to "eye up" that you a still drilling square.
Check that the drilling you have made looks central,if so ,with or without the head on drill out to 6.8mm.
If the hole is true you should have reduced the stud to a spiral down the hole.
With a plug tap try to pick up the existing thread,this is where it gets tricky,sometimes I've used a tiny chisel to pick up the start.You have to be really careful,bit at a time.
If all else fails providing you don't break the tap in it,you can helicoil it back to size
Check that the drilling you have made looks central,if so ,with or without the head on drill out to 6.8mm.
If the hole is true you should have reduced the stud to a spiral down the hole.
With a plug tap try to pick up the existing thread,this is where it gets tricky,sometimes I've used a tiny chisel to pick up the start.You have to be really careful,bit at a time.
If all else fails providing you don't break the tap in it,you can helicoil it back to size