Drill bits for metal work.

[fried1765]

A set Cobalt bits will stay sharp a little longer and get you through some of the harder metal. Look for a split point drill, it will cut a little freer. Larger diameter drills require lower rpm and high pressure. Small diameter drills will need higher rpms.

If you're using your bits in a hand drill, then you probably won't notice a difference between the high quality and cheap stuff. But if you're using them in a drill press or a mill, quality is the difference between 20 holes and a 1000 holes.

I´ve never used a Drill Dr, so I can't comment on how well they work, but having sharpened tens of thousands of drills in my life, I would say that sharpening drills is worth it if you are consuming a lot - but that's only the case if you don't wear them down too much before you sharpen them.

Cobalt bits are a BIG part of the solution!
Be CAREFUL though!
Many discount sellers will claim to have Cobalt or Titanium bits, but they are only coated bits (typically from China).
SOLID Cobalt bits are the best bits!

 

[marchanna]

Just to clarify. Cobalt is an additive in the steel chemistry, you won't find a solid cobalt bit. Titanium or TiN, TiCN, etc, are coatings that are gold or black in colour, and improve wear resistance. Sometimes these coatings are too thin or poor quality to actually have a benefit.

Solid Carbide drills however, are generally a super high performance drill. But there is a downfall with them also, they are very brittle. If you drop them on a concrete floor, they will break or chip. They should only be used in a controlled situation, such as a drill press or mill. Also, carbide drills are very expensive - expect to pay $20 - $30 or even more for a single 1/2" bit. A jobber drill set will likely cost several hundred dollars. Carbide drills are usually reserved for volume production and not regular job shop stuff.

Good brand names for Carbide drills are:
Guhring
Sandvik
Sumitomo
Kennametal
Mitsubishi
Kyocera

I'm quite happy with the Dewalt cobalt drills I bought and would recommend them.

 

[N80]

Thanks again guys. I am guilty of trying to drill too fast with larger bits. Will keep it slower in the future.

 

[/pine]

FWIW...It's a fairly common practice when drilling larger holes to start with smaller bits...i.e., for a 3/4" hole I usually start with a 1/4" or 3/8" bit...then a 1/2" then a 3/4"...

 

[mcfarmall]

Use High Speed Steel drill bits. Most people won't need HSS+Cobalt unless they are drilling stainless steel or some of the exotic alloys like Inconel, Titanium, Hastelloy, Waspalloy, etc.. Use cutting fluid either a synthetic water soluble type or petroleum based.

Also the general guide line "Go slow" is not a hard and fast rule. Going slow in certain alloys will cause them to work harden and then they will be impossible to drill. Use the starting point of 4X cutting speed divided by the diameter of the cutting tool to get your RPM. A general guideline is 500 RPM for low carbon steel with a 1/2" drill bit. As the bit gets smaller, RPM's go up, as the bit gets larger, RPM's go down.

 

[N80]

FWIW...It's a fairly common practice when drilling larger holes to start with smaller bits...i.e., for a 3/4" hole I usually start with a 1/4" or 3/8" bit...then a 1/2" then a 3/4"...

I always do that.

 

[LD1]

About any bit you get from industrial supply places are going to be good. Think grainger, MSC, mcmaster carr, Fastenal, Bowman, etc etc.

Hertle, PTD (precision twist drill) C-L (chicago latrobe), Cleveland twist, U-B are all a few good brands.

FWIW...It's a fairly common practice when drilling larger holes to start with smaller bits...i.e., for a 3/4" hole I usually start with a 1/4" or 3/8" bit...then a 1/2" then a 3/4"...

Maybe common practice among novice's that dont know what they are doing.

The WORST thing you can do on a drill bit is just this. It puts all the load on the outer corners of the drill bit....and the outer corners also have the steepest lead angle. It makes them really grabby and really likely to chip the cutting edges.

I HATE when I have to oversize a hole a little bit. Like going from 1/2 to 5/8 or 3/4. Just hate it. I cannot believe people willingly do this.

Drill bits UNDER 1/2" are usually split point bits. NO pilot needed. NO stepping up sizes.

Drillbits OVER 1/2" are typically a chisel point. And nothing more than a pilot equal to the web thickness (width of the chisel point) is all thats needed. Usually around 1/4" works well.

Forget stepping up sizes unless you enjoy buying bits to replace the damaged ones, or enjoy the drill being ripped from your hands

 

[/pine]

About any bit you get from industrial supply places are going to be good. Think grainger, MSC, mcmaster carr, Fastenal, Bowman, etc etc.

Hertle, PTD (precision twist drill) C-L (chicago latrobe), Cleveland twist, U-B are all a few good brands.



Maybe common practice among novice's that dont know what they are doing.

The WORST thing you can do on a drill bit is just this. It puts all the load on the outer corners of the drill bit....and the outer corners also have the steepest lead angle. It makes them really grabby and really likely to chip the cutting edges.

I HATE when I have to oversize a hole a little bit. Like going from 1/2 to 5/8 or 3/4. Just hate it. I cannot believe people willingly do this.

Drill bits UNDER 1/2" are usually split point bits. NO pilot needed. NO stepping up sizes.

Drillbits OVER 1/2" are typically a chisel point. And nothing more than a pilot equal to the web thickness (width of the chisel point) is all thats needed. Usually around 1/4" works well.

Forget stepping up sizes unless you enjoy buying bits to replace the damaged ones, or enjoy the drill being ripped from your hands

FYI...excuse me mr omnipotent (whom I've noticed does not seem to know the difference between "weather" and "whether")...but I have been using the same bits for many years using the method described...

As the drill size increases, both the size of the web and the width of the chisel edge increase (Figure 6-34). The chisel edge of drill does not have a sharp cutting action, scraping rather than cutting occurs. In larger drills, this creates a considerable strain on the machine. To eliminate this strain when drilling a large hole, a pilot hole is drilled first (Figure 6-34) and then followed with the larger drill. A drill whose diameter is wider than the web thickness of the large drill is used for the pilot hole. This hole should be drilled accurately as the larger drill will follow the small hole.

General Drilling Operations | Smithy - Detroit Machine Tools

 

[dmccarty]

...

Solid Carbide drills however, are generally a super high performance drill. But there is a downfall with them also, they are very brittle. If you drop them on a concrete floor, they will break or chip.
...

The logging company who bought our timber years ago was owned by two men who I will call Too Short and Too Tall. The names have nothing to do with their height. :confused3::shocked::laughing::laughing::laughing:

The foreman on the job ran the huge machine that cut down the trees. The teeth on the cutter were made of carbide so they would stay sharp for a long period of time.:thumbsup:

The foreman's problem was Too Tall and Too Short.

The Too Tall boss would tell the foreman to cut closer to the ground to maximize log length and thus revenue.

The Too Short boss would tell the foreman to cut farther up the tree so that the carbide cutter teeth would not hit a rock which would require replacing and thus increase expenses.

You could tell from the stumps which boss man had been on site when a tree was cut. Some stumps were just about ground level and others were a half foot above grade. :laughing::laughing::laughing:

The foreman was never right on his cutting length. :laughing::laughing::laughing:

Later,
Dan

 

[marchanna]

There's more than one way to skin a cat . . .

The old drill catalogues used to contain tables in the back for drill type, drill size, material being drilled, and speeds and feeds. They would get you 90% there, 90% of the time. For a production process, experience + trial & error, gets you the rest of the way to optimize a balance of performance versus cutter life.

Generally, if you're pre-drilling a hole to rough it out first, you are going to follow it with a core drill, not a standard 2 flute twist drill. Also, it is generally more desirable to drill with a single tool into solid billet or cast, then if necessary burnish or ream. It all depends on what you're doing.

I am guilty myself of piloting then chasing with a larger 2 flute twist drill, but I do this expecting that I will likely ruin the larger drill - usually because of chatter.