OK I am trying to drill through like 8 or 9 guage stainless - basically cold rolled double angle section ... extremely hard and pretty much work hardened to hell and back ... about 3/32's thick. OK I have lost a whole handful of drills ... I get 1/2 way through and the metal turns cherry red, and makes a screeching noise and nothing happens ... and the drill gets blunt ... Yea Its that hard ... Its hard to cut as well, hard to de burr but I managed all that ... drill is the final step ... So ... any ideas ... what drills to use ... cobalt ... titanium ... what ... Need a 5/8th dia hole ...
Cool.
Srinath.

Use A LOT of coolant and try a different speed, with thick steel you must be patient and go a little bit at a time. As for specifics I found in my machining text for High strength stainless the point should be crankshaft (a standard point would work but not as well) a Point angle of 118-135 degrees, a lip relief angle of 7-10 degrees a chisel edge angle of 120-130 and a heliw angle of 24-32 degrees...this is about the same type of bit you would use for titanium so a carbide bit would probably be the best but they are usually expensive so titanium would probably do the job... I hope this helps

good cobalt should be fine,

center punch the spot for hole, use a small diameter bit like 1/8", the cutting area is small and heat has time to spred out to colder area's of the metal, slow speed and oil helps alot too. up grade to like a 5/16 then to 1/2" and then to 5/8'  each bit is then not haveing to work as hard, its not cuting as much an area at one time and heat has a chance to move away. the big thing is taking your time.

Oh Bluknyt ... that reminds me ... I have a center punch from 1/2 inch stainless rod, sharpened to a point ... and that hardly made a scratch when I punched it ... I gotta buy a bunch of drills anyway .... cobalt it is ...
Cool.
Srinath.

Did you try a really small hole first?

Then step up the bit size 1 at a time until you get up there?

Can you fit a punch into the hole and get another starting point?

Last thing I'll say.
What about getting some dry ice and freezing it to make it more brittle.  (might help, and I mean with dry ice)

Use a good drill bit.  HSS is fine.  Union Butterfield, American twist drill, Irwin, etc.  

Spindle speed between 300 and 450 RPM.

Clamp the work to prevent chatter.

Use a backup plate to keep the metal from bending.  Any old piece of flat scrap around 1/4" thick will do.

It's probably going to take 1.5 HP to drill that.  A good drill and a good drill press will go right through it.  Use coolant if you have it.  If not motor oil will work, it's not a deep hole. (dirty field technique).  

Tip:  If a drill press is chattering or the cut is making anything more than a "hissing sound" you're not pushing hard enough!  The chips should spiral unless the bit has chipbreakers.  If the drill stalls the drill press isn't big enough.  Step drill or use a bigger drill press.  

Geep has the formula.  Also, it takes a fair amount of pressure to drill this stuff.  As soon as the bit contacts the metal, add pressure.  Otherwise, the bit will loose its edge almost imediately.

DO NOT try to remove burrs of shavings with your hand/fingers!!  The will cut you bad, man.   Surgically sharp.

OK I'll try it  ... and yea the burr ... I have rather painful cuts on 6 fingers, 5 of whihc drew blood, and I have burnt one ... Today is going to be warm and nice, and turns into wet and cold for the next 3 days ... so I have to let it all heal up ...
Cool.
Srinath.

On "American Chopper"(I know, don't laugh  :lol: ) they use a stepped drill bit to drill a lot of things. It looks sort of like a plumb bob, it starts small and steps up to a larger hole all with one bit.

Derek

The stepped drill bit that looks like a plumb bob is called a Unibit and they are made by Irwin.  They make about six different types, of which I have four,  but I believe the only two most common types are available at Home Depot, the 1/2" and 1" with 1/8" increments.  I suggest lots of cutting fluid, lots of pressure(from a drill press) and low rpms.  The Unibit is really the best way to get a good 5/8" hole in stainless unless you have an end cut mill bit.  Using regular two fluted bits will sometimes give you a triangular shaped hole if you don't remove alot of material first with smaller drill bits, but stainless is damn hard and you'll need to clamp the piece down and use a high torque drill if you go that route.  Good luck.  

All of the above, If you can get a buddy and one of those long-snout oil cans get the mate to drop oil onto the job, I have seen a pro set-up for this and they used a mixture of oil and water as coolant - lubricant, they had a continuous feed of the emulsion.

OK I used liberal amounts of 3m cutting fluid and I didn't listen to my welder ... ( he suggested faster drill speed ... I had it close to 800 rpm or more) and Yea first 1/8th then 1/4 then 3/8th then 5/8th ... worked great ... OK touch wood ... still have 2-3 sets to go ... but still on drill #1 ...
Cool.
Srinath.