Originally Posted by sailvayu
The trick is water. Keep a steady stream of water on the bit to keep it cool. Never let it get hot. Oil burns off too fast. You will be able to do all the chain plates with 1 bit it might need resharpening a couple of times but you will only need the one. I have done this and I know it works. You can also cut stainless with a saber saw keeping a stream of water on it. Don't believe me try a test piece you will be amazed it cuts and drills just like carbon steel. Slower speeds help too keep the heat down it is all in not letting the cutting tip get hot at all.
Finally, someone got it right. As a Machinist of 45+ years I can tell you it's not a fun drilling SS, especially the 303/304's. I dread 347 and some other aircraft stuff.
But any way, colbalt drill bits are best. Carbide is too expensive and has to be total controlled at hi speed to keep from chipping them.
The secret is a slow speed and continuos pressure until it's about to break thru, then ease off for the final pass. The object is to not get the metal hot. It's called work hardening. The heat causes the carbon to transfer from the bit to the metal making the metal as hard or harder then the bit itself. SS is one of the worse metals for this due to it's bond. It's a catch 22. The hotter it get the harder it gets, the harder it gets the hotter it gets.
I use what is called a spray mist, a mixture of a coolant and a jet of air. Submersed in water is OK too just not easy to control on drill presses and knee mills.
The drill angle on colbalt drills is 135º with a split point that can not be resharpened properly/accurately by hand w/o diamond wheels.
If you can not see the flutes of the drill plainly as it turns, then it's going too fast. If it starts to squeal then it's getting dull and you need to get another drill and run it even slower.
But remember "continuos pressure" to the last little bit. When the drill breaks thru it creates more heat then during actual drilling.
Pilot holes are recommended if one can not put enough pressure to keep a chip flowing. Trying to hand drill anything over 3/8" dia., I'd recommend a pilot drill of 1/8". A 1/2" drill by hand I'd pilot with a 1/4" drill bit. Trying to drill anything over 1/2" could be hard on the wrist.
A 3/4" by hand I'd pilot it twice. And even then could be rough if it grabs.
Remember keep the cool chips flowing.