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How to Choose Twist Drill Bits

Confused about drill bits? So were we. So we tested high speed steel, black oxide, cobalt and titanium bits in wood and metal, and here's what we found out.

By the DIY experts of The Family Handyman Magazine

How to Choose Twist Drill Bits

Confused about drill bits? So were we. So we tested high speed steel, black oxide, cobalt and titanium bits in wood and metal, and here's what we found out.

Drill bit test results

I headed into my highly sophisticated drill analysis laboratory (my garage) and scientifically tested four types of 3/8-in. twist bits: a $2.75 high-speed steel bit, a $6 “black oxide” bit, a $7 cobalt bit and a $9.50 titanium bit. Using each bit in a drill press, I drilled 75 holes in pine, 40 holes in oak, 20 holes in aluminum tubing, 20 holes in medium-density fiberboard and five holes in 3/16-in. mild steel.

All of them finished the test without dulling appreciably. The high-speed steel bit was a little choppy on the last 20 holes in the pine, and all the bits except the titanium one tended to wander and bore oversized holes in the aluminum. But if you're a less-than-160-hole-drilling do-it-yourselfer, working mainly in wood, you can get by with any of them. As one carpenter put it, “In my book it doesn't really matter—I usually lose them or snap them in two before they have a chance to dull.”

To complete the test, I drilled holes in the steel with each until they dulled and became useless. The score? The high-speed steel bit was shot after 20 holes. The cobalt and black oxide bits were still boring after 25 additional holes, but with substantial effort on my part. The titanium bit just kept drilling an endless line of perfect holes—my arm gave out before the bit did.

Note: A bit's composition isn't the sole determinant in how well it bores through metal. In general, bits with “flatter” tips drill quicker, last longer and have less “walk” than those with “pointier” tips.

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Comments from DIY Community Members

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February 22, 5:35 PM [GMT -5]

As others have said, there are other variable to be taken into consideration. One thing I noticed in your picture is that the bit on the right has a "slower spiral" than the others. This refers to the angle of attack of the cutting edge at the tip, and is visible as the amount of flute rotation per inch of drill. Faster spiral drills are good with soft metals like Aluminum, which create a "stringy" chip that tends to clog the drill when cutting. Different coatings are also good for different things. For example, aluminum cuts better with no coating. For thin materials, 135 degree drills get into the material faster, so they seem to cut faster. They also have a faceted grind for better centering. But conventional 118 degree drills with no facets center better if you like to use pilot holes.

March 13, 1:02 AM [GMT -5]

The coating (titanium) is only microns thick, it is put on as a vapor coating. If you look at the shank of a titaniun coated drill you will see that on most of them that the shank is not coated. You would have a tough time feeling ridge at the edge of the plating.

March 13, 12:06 AM [GMT -5]

After spending more than 30 years as a Tool & Diemaker I agree 100% with the results of your intensive testing. I also agree with the usually lose them or break them saying.

September 13, 7:59 AM [GMT -5]

I have a question concerning the titanium bits you used and this concerns the basic material the bits were made with. This shows some ignorance on my part because I am unaware of just how they make all bits. The material used to make titanium bits, is it made of 100% titanium or is there a titanium coating on the bit and if so how thick is it? I have often seen ads stating that the bit is titanium coated. This question really applies to the all other types of bits tested.

September 05, 8:01 PM [GMT -5]

When cutting into wood and engineered wood and laminates the drill performance is a function of the tip material, tip design, and flukes, all of which can vary widely. For the fastest drilling and the greatest number of holes before sharpening the best drill bits have a tungsten carbide tip and flukes that are wider than the area between them which provides fast cuttings removal with any material.

Cobalt, tungsten, high speed steel (M2, M3, M42), or tungsten carbide (more that a dozen grades commonly used for shop tools) makes a big difference in materials such as mild steel, stainless steel, and fiberglass or FRP, and fiber cement board (Hardie, etc.), but this is not a factor with wood or engineered wood products. Unfortunately the tester did not understand this and add tungsten carbide tipped drills to his test.

Equally important is drill speed and the use of a cutting fluid. With stainless steel for example the higher the drill speed the more the metal is tempered and as it becomes harder the drill's performance decreases dramatically, which is why with stainless the drill speed should be half of that used with mild steel.

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