if your hand tapping, start with a spiral point as far as you can get, then use another tap with the tip ground down to get to the bottom threads.
And use good taps, this will make all the difference in the world. One of my local suppliers specializes in hard material tooling. I just walk in, tell him what material I'm tapping and he has diffrent grade OSG taps. Said he has taps for up to 60 Rc.
Not too long ago, I had some 304 plate and needed 3/8-16 threads all the way thru. Just for fun, I tried one of my normal HSS taps that I use for MS and AL, it ripped the teeth right off the tap and barely touched the SS. Went to my supplier and bought the OSG tap, told the salesman I was cutting 304, went through like it was cutting butter, total night and day difference. I later asked the salesman what the taps were made from to make them cut hard material vs. a HSS tap, he said Vanadium.
A while back I bought some endmill holders and wasn't impressed with the 3/16" set screw in the side. So, I used a carbide endmill to open up the minor, bought a OSG tap for hardened tool steel, no problems at all. Again, HSS wouldn't touch it.
Spend a couple of bucks on the right tools and you won't have a problem. 303 isn't that tough, but that is a small thread too.
MC  |