Screw Machine Drills vs Cobalt Screw Machine Drills

[Patrice Lemée]

I need to order a bunch of drills and I was wondering if it is worth the money to get the cobalt ones. This is not a coating I believe, but Cobalt HSS.

Screw Machine Drills: HSS - 118° POINT – Ground polished flutes – Precision Twist Drill Co. USA
Cobalt Screw Machine Drills: Cobalt HSS - 135° SPLIT POINT - Precision Twist Drill Co. USA

The Cobalt ones are about twice the price of the regular ones. Of course we are not talking a lot of money individually, up to maybe 3$ more for the larger ones, but on the entire order (around 50 drills) it is still a bit of difference.

Just wondered what do you guys think?

Thanks

 

[Busto]

Patrice get the Cobalt....they are not HSS....I buy my small drills by the dozen because its not worth the time to resharpen. Cobalt will outperform HSS 3:1. I have some Cobalt #7's that are pilots for
1/4-20 bolt holes that I've been using and sharpening for a couple of years. Cobalt will work on tempered steel as in a tang that was hardened and drawn but HSS will just sit and burn up.

 

[Patrice Lemée]

Thanks Busto, I'll go with cobalt then.
You say hardened steel? How do they compare to carbide?

 

[Don Hanson III]

Cobalt Screw Machine Drills: Cobalt HSS - 135° SPLIT POINT - Precision Twist Drill Co. USA

These are what I use and have used for over 15 years.

 

[Busto]

Thanks Busto, I'll go with cobalt then.
You say hardened steel? How do they compare to carbide?

They are just a tick below carbide. The real difference is that with hardened depending on RC # cobalt run slow with plenty of lube will work and not chip like carbide. I have only a couple
of carbide bits real small 3/32" but do most everything with the Cobalt. If you temper back back to blue or peacock on your tang cobalt will have no problem.

Mike

 

[JG Custom Metal Works]

Just as an addendum to the info already given, you might look at getting a Drill Doctor(if you don't already have a method of resharpening bits). I got one a while back from an estate sale for $15 and it's been a godsend. I've restored a ton of old bits and they make nice long spiral shavings.

 

[Busto]

Just as an addendum to the info already given, you might look at getting a Drill Doctor(if you don't already have a method of resharpening bits). I got one a while back from an estate sale for $15 and it's been a godsend. I've restored a ton of old bits and they make nice long spiral shavings.

I've been a machinist for 30 years and my first job was to sharpen the "Old Man's" drill bits on a grinder....I mean like 2 weeks straight of sharpening bits...He figured if I stuck it out he would train me on everything else....to this day I hand sharpen all my big bits on a tool grinder or with my KMG belts....I just toss the small Numericals (49's/50's etc) Guess I did an ok job on his bits huh?!!!!

 

[Patrice Lemée]

Thanks guys, exactly what I needed. :thumbup: If it's good enough for Busto, a 30 year machinist, and Don, well it sure is good enough for the me.

Busto, I needed something for the blade itself and from what you tell me, I am still better off with carbide there because of the high HC. I'll still get a few for the tang though.

About the Drill Doctor, I do have one of those. Not a great fan. They are hot or miss from what I have gathered. Mine does ok on the lip but not the clearance angle. Doesn't even grind one. I do it myself on the grinder after using it to cut the lip.
I also started practicing doing it all by hand but without anybody to show me hands on, it's taking a bit more time to get the hang of it. But I am slowly getting there, I do a good job maybe 2 times out of 3.

Thanks again for the recommendation, I will order only cobalt drills from now on.

 

[ridges]

Thanks Busto, I'll go with cobalt then.
You say hardened steel? How do they compare to carbide?

In my experience they don't.

Cobalts are great, massively superior to plain HSS bits which struggle with even annealed high alloy steels but they are nothing compared to carbides. I tempered some O1 to blue and drilled it with a brand new cobalt bit and it took forever and the drill bit was pretty chewed up after. Carbide on the other hand will cut 65rc like it's butter.

 

[Nathan the Machinist]

A 135 degree point has less edge in the cut and generates less chatter. Those drills tend to have a thicker core for higher stiffness. The split point can penetrate harder materials and reduces work hardening and heat.

A short cobalt HSS 135 degree split point drill is the best drill for difficult materials like knife steels.

That said, for all my fancy machines and cutters and techniques, I still use the humble 118 jobber drill in production in knife steels and run them hard and cut many feet of hole in some nasty stuff with them. If you're cutting annealed material, any quality drill will usualy work okay.

 

[Busto]

Nathan's right on the money short 135's are the ticket....Agreed that Carbide will cut hardened steel better and is the reason I have small carbides for doing bolsters on hardened Stainless.

Patrice its not a bad idea to have one or two carbides just in case after heat treat you need to drill the blade....I've been there myself....

Mike

 

[Patrice Lemée]

Ridges, I'll definitely get some carbide for high HC.

Nathan, pretty sure you could use a wet noodle and still do a good job of it. Being a Hack myself, I need all the help I can get. So I'll definitely get some of those 135° cobalt screw drills. Keep the jobber for the really soft stuff and practice shortening drills by hand.

Mike, believe me I've been there myself too and will surely be again, hence the handful of carbide drills in my order. Looks like what started as “I need a few drills” will turn into a 600$+ order.

Thanks again guys.

 

[Methuselah]

A 135 degree point has less edge in the cut and generates less chatter. Those drills tend to have a thicker core for higher stiffness. The split point can penetrate harder materials and reduces work hardening and heat.

A short cobalt HSS 135 degree split point drill is the best drill for difficult materials like knife steels.

That said, for all my fancy machines and cutters and techniques, I still use the humble 118 jobber drill in production in knife steels and run them hard and cut many feet of hole in some nasty stuff with them. If you're cutting annealed material, any quality drill will usualy work okay.

what a great quote

 

[Methuselah]

A 135 degree point has less edge in the cut and generates less chatter. Those drills tend to have a thicker core for higher stiffness. The split point can penetrate harder materials and reduces work hardening and heat.

A short cobalt HSS 135 degree split point drill is the best drill for difficult materials like knife steels.

That said, for all my fancy machines and cutters and techniques, I still use the humble 118 jobber drill in production in knife steels and run them hard and cut many feet of hole in some nasty stuff with them. If you're cutting annealed material, any quality drill will usualy work okay.

what a great quote , i'm talk ing about the man on fire quote.

 

[mike-E]

I've been a machinist for 30 years and my first job was to sharpen the "Old Man's" drill bits on a grinder....I mean like 2 weeks straight of sharpening bits...He figured if I stuck it out he would train me on everything else....to this day I hand sharpen all my big bits on a tool grinder or with my KMG belts....I just toss the small Numericals (49's/50's etc) Guess I did an ok job on his bits huh?!!!!

this is exactly how i started out. hand ground them all on a big pedestal from 1/4'' all the way to 4'' drills that were chopped off after being broken. to this day i dont even use the big drill pointer in our shop, it's too slow.