Turn the tap only 1/16 of a turn in then out a couple of times to set and clean the threads before cutting another 1/16th turn. When the tap's taper is all the way in the hole and the full width having cut about 2 full turns and the progress feeling OK, then we can increase the turn to 1/4 turn in and out for each cut until the taper fully exits the other side end of the hole. Any time the cutting doesn't feel nice, easy and smooth, ....then stop and make sure such resistance is normal for the old threads conditions. |