90 degrees to the hole.... eek!
Make sure it is straight and true to the origional hole. Not crooked in any way. Go slow with a tap and always keep moderate pressure pushing it into the hole. Do not let the threads it is cutting "pull" it into the hole. That will give you a bad thread cut. Proper tap cutting oil is best, but even WD40 (ugh
) will work in a pinch. As previously said, always turn it in 1/4 to 1/2 turn and then turn it backwards a 1/2 turn to break the newly formed metal chip. If you do not do this the tap will become overwhelmed and snap off in the hole! It is not a fancy drill bit......
Good luck, and be patient!