cobalt high speed drill bits

[CobraChevelle]

tired of burning up cheap china drill bits. And yes I am using cutting oil.

looking @ buying a 29pc cobalt drill bit set. I have sold these to people for drilling stainless and they seem to like them.

My question is these seem to work best @ 1500 rpm or higher. Now some of my drills are high amp but low rpms like 700. How will this work? will these be a waste of money?

 

[neophyte]

Cobalt drill bits are for high heat, hard material, drilling situations. Different types of stainless steel, and other specialty alloys may require different drill bit materials, drill bit finishes, and flute geometries.

The main advantage to Cobalt steel is hardness and the ability to retain the hardness despite the drill bit getting very hot in use. The main disadvantage is the Cobalt steel is more brittle than some other types of high speed steel. Most cobalt steel drill bits also use a thicker web geometry that won't clear chips as well.

A lot of people swear by the USA made Magnum drill bits that Norseman sells. The Magnum bits aren't cobalt steel, they're made out of M7 high Molybdenum steel, that is tougher and harder than the regular HSS good drill bits are usually made from. The Magnum bits also use a more open flute geometry that allows for better chip ejection. If you're drilling with a drill press, and items firmly clamped the cobalt might be a good choice. If you're drilling freehand you might be better off with the Magnum bits.

This is a description concerning the drilling performance in stainless, between Cobalt and the M7 Magnum bits.

"Work hardening grades of stainless are the 300 series with the exception of 303, which is free machining. Free machining grades include the 400 series in addition to type 303. A quick way to identify work hardening vs. free machining stainless is to observe the chip formation. Work hardening chips break up during the drilling process, while free machining chips are long and stringy."

 

[doan]

tired of burning up cheap china drill bits. And yes I am using cutting oil.

looking @ buying a 29pc cobalt drill bit set. I have sold these to people for drilling stainless and they seem to like them.

My question is these seem to work best @ 1500 rpm or higher. Now some of my drills are high amp but low rpms like 700. How will this work? will these be a waste of money?

Northern has a nice cobalt set on sale for $100 now, 80 if you have a coupon.

Discussion in hot deals: www.garagejournal.com/forum/showthread.php?t=287810

I got a set, best drills I've ever used in metal.

 

[BFHtime]

I have found that drilling hard items works better with slow speeds, and plenty of cooling. Cooling with cutting oil or just about any spray lube, or even used oil. Thicker oils have a tendency to pull the chips away, assembly lube for example. Fast enough not to stall is, is fast enough, anything more with increase friction. Keep steady pressure, while applying plenty of cooling cutting oil.

 

[ez-duzit]

tired of burning up cheap china drill bits....
these seem to work best @ 1500 rpm or higher. Now some of my drills are high amp but low rpms like 700. How will this work? will these be a waste of money?

You should know better than to buy Chinese drill bits.

1500 rpm? Says who?

There is an optimum speed for each material being drilled and therefore an optimum rpm for each drill bit size.

High speed steel cuts common steel at ~100 feet/min. So optimum drill motor speed is 4x100/.5=800 rpm for a 1/2" drill. 4x100/.125=3200 rpm for a 1/8" drill. (note: 4 is just a factor)

Or you can look it up in this chart.
https://www.fnal.gov/pub/takefive/pdfs/Drill_Press_Speed_Chart.pdf

Cobalt for hard metal like stainless.

The life of your drill bits is governed by running time (if you don't break or chip them). If you use an improper low-rpm drill motor with your smallest bits, they will need more frequent resharpening.

If you're drilling steel and stainless, use a drill press.

 

[leg17]

You should know better than to buy Chinese drill bits.

1500 rpm? Says who?

There is an optimum speed for each material being drilled and therefore an optimum rpm for each drill bit size.

High speed steel cuts common steel at ~100 feet/min. So optimum drill motor speed is 4x100/.5=800 rpm for a 1/2" drill. 4x100/.125=3200 rpm for a 1/8" drill. (note: 4 is just a factor)

Or you can look it up in this chart.
https://www.fnal.gov/pub/takefive/pdfs/Drill_Press_Speed_Chart.pdf

Cobalt for hard metal like stainless.

The life of your drill bits is governed by running time (if you don't break or chip them). If you use an improper low-rpm drill motor with your smallest bits, they will need more frequent resharpening.

If you're drilling steel and stainless, use a drill press.

For less than ideal machine shop situations, you may want to start at about half of the ideal RPM and work your way up.

IF IT CHIPS, YOU'RE TOO SLOW.
IF IT BURNS, YOU'RE TOO FAST.

 

[ez-duzit]

And, with stainless, once you start the chip going, keep it going--don't let up the pressure and try to restart.

 

[PT Doc]

I second the Norseman brand. They produce any set you could want, with great quality, value and Huot indexes. Patrick at ISC suppy has been a great guy to deal with for the group buys that we had last year.

If there is enough interest, we would do it again for the gj community.

 

[404]

In addition to the good advice above regarding the surface feet per minute (sfm), One MUST force a feed rate from the very start.
If the drill is allowed to rub over the SS for even a moment, the SS under the bit work hardens in a thin layer on the surface directly under the bit. This work hardened layer may be near the hardness of the drill bit.

Same problem happens if the drill is paused in an existing hole while turning. The material will work harden.

So either be making a chip, or have the drill out of the hole.

I would say if a drill bit chips the feed rate is too high. With enough machine behind a drill bit one can drill in slow motion.

 

[PT Doc]

Good point 404 made. I feel that newcomers to drilling with drill presses are not feeding hard enough. They rub the bit and wonder why it won't cut. Just feed the thing and make chips.muse some cutting fluid and life will be good.

 

[Adam.C]

Beware. I think I recall seeing chinese bits advertised as cobalt, but were some low grade steel instead. A set of real M-42 bits should cost upwards of $200.

Chinese bits are so terrible, I don't think I would go from them to US made M-42. Instead, start with US made HSS sharpened 135 split point. Buy only the U.S. made bits from an industrial supply house such as Enco, MSC, Grainger, or McMaster. These will cost about $50. Forget big box store drill bits.

The keys to successful drilling are having the right bits, right feeds and speeds and having SHARP drill bits. Even some woods dull drill bits. Another alternative ISO get yourself an expensive drill doctor and buy good quality drills second hand and sharpen them yourself. You will need the sharpener eventually anyway.

Disposable drills never work well on metals and really aren't even economical.

 

[LordPsychon]

In addition to the good advice above regarding the surface feet per minute (sfm), One MUST force a feed rate from the very start.
If the drill is allowed to rub over the SS for even a moment, the SS under the bit work hardens in a thin layer on the surface directly under the bit. This work hardened layer may be near the hardness of the drill bit.

Same problem happens if the drill is paused in an existing hole while turning. The material will work harden.

So either be making a chip, or have the drill out of the hole.

I would say if a drill bit chips the feed rate is too high. With enough machine behind a drill bit one can drill in slow motion.

It's probably also advisable to use a decent drill press versus a cheap one - better chucks = better grip. The travel length of the quill and spindle may play a role but this is more suspicion than knowledge.

 

[Adam.C]

It's probably also advisable to use a decent drill press versus a cheap one - better chucks = better grip. The travel length of the quill and spindle may play a role but this is more suspicion than knowledge.

You are correct to a point. Chinese drill presses have notoriously bad spindles. This leads to oversized holes, out of square holes, especially when the spindle is out of square with the table, and holes out of round.

One thing you can do is tune your drill press, shimming the head as necessary to make it square with the table. Always a good idea to center punch the work to help the drill find center.

High quality drill chucks, in addition to gripping better, add less slop or runout.