tapping blind holes

[moore716]

if you look at the end of a standard tap you will see that its tapered and does not cut on the end. If you are tapping a blind hole you either need to drill it extra deep of make a bottom tap. I have access to lots of taps so this is easy for me. I use a regular tap to start the threads and then switch to a bottom tap to finish it out. To make a bottom tap just grind off the majority of the tapered uncutting end of the tap. Leave a little taper or it will not start in the hole very good. You can also grind a small slot across the end to help clear the chips. sorry I dont have any pics of the ones I've done they are at work.

Bonus Tip**Always oil the hole very well when tapping. You will get to a point when the tap gets hard to turn. To prevent snapping it off turn the tap 1/4-1/2 a turn backwords and then go fwd again. if you back out the tap slightly when it gets hard you wont break them off anymore.

[90GTVert]

Good tips. I back the tap out completely and clean it and the hole out if it's stubborn. Restart. Should be easy to get it going again as long as you've cut a few threads already.

[stepthrutuner]

Good tip on making a bottom tap from a through tap. I would add to be careful grinding the tip away, i.e., don't get it too hot so that it loses it's temper. Keep a container of water near the grinder and dip the tap in it very frequently before it even gets much past warm.