Carbidetipped drill bits for finishing up a problem drilling operation

I'm an auto mechanic here in Pennsy & was drilling through steel a while back, on a car I was repairing, & encountered, about halfway through the material, a squealing/ringing sound. The bit kept turning, but stopped progressing. One of the guys, who had been a metal fabricator, told me that the squealing sound indicated metal that was too hard for the bit in question & that I was screwed. I finished the job somehow & figured that I had run the bit too fast, applied too much pressure, or maybe the bit was on its last legs to begin with.

2 days ago I was drilling frozen bolts out of an exhaust pipe flange with a brand new Snap On cobalt. I ran the drill slow, kept it cool, & didn't use too much pressure. About halfway through I heard the dreaded squealing sound again & the bit continued to turn, but basically stopped progressing. I got through with a carbide burr, but the result was a butchered hole, since I guess the burrs aren't as "precise" as a fluted twist drill bit.

So I wanna get some carbide tipped bits. Checked out a 29 Pc set online, 1/16" to 1/2", with 1/64" increments. 5 bills. Oh, Mama! So I decided on just 6 bits: 1/8", 5/32", 3/16", 1/4", 5/16", & 3/8".

I can't decide if I want 118 degree or 135 degree split point. I always use a pilot hole, so maybe the split point, whose advantage is that it stays centered, might be unnecessary. Also, I gather that the 118 degree bits require less pressure on the hand drill to cut, what with their more "pointed" angle--I'm 60, & my arm gets tired quick pushing on that drill!

Any thoughts re 118 vs 135?

the stop in progression your speaking of is work hardening. the drill probly rubbed from lack of pressure and hardened the material. drills like good stready feed.

135 is nice but if you dont have a speed/feed chart get one of them too

remileblanc said:

the stop in progression your speaking of is work hardening. the drill probly rubbed from lack of pressure and hardened the material. drills like good stready feed.

Click to expand...

Yup. +1
You need to watch the chips being removed. If you're not getting the right amount of material removal, you can end up heating the steel you're cutting to, causing it to get hardened and burnished.
In this case, you were probably not pushing hard enough, and were drilling in an alloy that hardens. If you push hard enough, you will remove chips as you're heating the surface, but you'll keep cutting through the hardened area.

Anyway, you're much better off investing in a Drill Doctor, than in carbide tipped bits.

Are you using any sort of cutting fluid? Tapping fluid works, rapidtap, etc.

And ditto what was said above, try need a steady feed that makes a nice chip, otherwise they dull out from rubbing, not cutting.

Go 118. Carbide bits are too damn expensive to be un-resharpenable (you can resharpen 135's by hand, but it takes a LOT more skill), plus the shallower corner angle on the 118 will be more resistant to chipping.

135's cut easier and drill more precise holes, but they also break/chip more easily when drilling through uneven surfaces or multiple layers of different thicknesses. The 135's cutting edge is thinner, and the angle at the outside cutting edge is sharper, so more brone to breakage.

Thanks for everyone's responses! I'm starting to understand that proper drill work is more an art than a science, especially with a hand drill. I can see now how giving steady pressure gets rid of material before it can heat/harden. Maybe I'll have better luck in this area from here on.

You learn something new every day, & if you don't it's a wasted day!