On Tuesday, July 14, 2015 at 8:51:06 AM UTC-7, Cydrome Leader wrote:
jon_banquer wrote:
On Monday, July 13, 2015 at 3:46:47 PM UTC-7, Cydrome Leader wrote:
jon_banquer wrote:
On Monday, July 13, 2015 at 12:18:02 PM UTC-7, Cydrome Leader wrote:
Ned Simmons wrote:
On Mon, 13 Jul 2015 16:59:44 +0000 (UTC), Cydrome Leader
wrote:



I suspect it has something to do with the angles they bits are cut. The
cobalt stuff from a good hardware store is usually 135 degrees. I seem to
wear the tips out real quick, large or small. Never really figured out
why.


Are you wearing the edges or chipping them? Common high speed steel
(M2) is tougher than cobalt high speed steel (M42). M42 is more wear
resistant and has higher heat tolerance. The edges on M42 drills will
chip much more easily than common HSS drills, so I don't personally
think they're a good choice for general use in hand drills.

It's wear. The tips go dull and seem worn as If I drilled into a brick or
something.

What RPM are you running the drill at?

various speeds- I've had this happen by hand with 1/4" bits and well as in
a Cameron drill press- so the bit in that must have been around 3/32" in
that case. Not enough feed pressure and I'm just spinning/burning the bit?
They bits were all used on stuff like Al, brass and plastic, some steel.
It's obvious pretty quick when a drill bit is dulled, and it's always the
cobalt stuff that ends up in the dull pile.

Never had this problem with genericy black oxide or HSS bits, pretty sure
all of those that I have are 118 degree though. Why are the cobalt ones
always 135 degrees in the first place?

135 degree cobalt split point drills are self centering. 135 degree drill bits are used for drilling into hard materials. They will last much longer on hard material. I often use 135 degree split point American made cobalt stub drills if I don't want to center drill first and position tolerance is .002 or greater.

The "coating" of hot rolled steel is often very abrasive. My choice for hand drilling would be a sulpher type oil not a water soluble oil. Be careful not to use too high an RPM or to light a feed.

Cobalt drills will take more heat before the cutting edge breaks down but they will chip easier if you force them.

I centerpunch first, but maybe the flatter angle of the 135 degree bits
don't even land in the punch mark or something.

Anyways, I did order some of the ws-5050 stuff from Enco, and I'll try it
and the standard pipe thread cutting oil just for fun. Getting my saw
aligned to 90 degrees resulted in a small scrap pile to experiment on.

Good drills are expensive. USA made Cleveland and Precision Twist Drills are the drills I use most of the time. I have them in letter, fractional and number sets. They aren't cheap but they have done nothing but make me money with no hassles.