Twist Drill Bit Information

Sep 28th 2021

Twist Drill Bit Information

Drill Bits

Labeling / Part #

There will often be labeling on the shank of a drill bit, and nearly always on the case when there is one. This labeling may provide many of the specifications if researched online.

.

.

Material

HSS (High Speed Steel)

High speed steel (often referred to as "HSS" and sometimes "HS") is the most common drill bit material. It is cost effective and works well for many general purpose applications. If the bit is coated, you may have to look at the base of the shank for the color of the material.

.

Cobalt:


Cobalt drill bits will have a brighter, almost golden color. They are not used for general purpose, but for withstanding very high drilling temperatures and hard abrasive materials.

.

Carbide:


Carbide will have a darker gray appearance when uncoated, but can look quite similar to HSS. The biggest way to tell carbide apart from other metals, is that it is extremely heavy weighing twice as much as steel. Carbide is popular for its wear resistance and toughness, as well as its ability to be manufactured into many shapes.

.

.

Coating

TiN (Titanium Nitride)

TiN is the most common coating, and can be used for many applications. It increases wear and deformation resistance and will have a golden color. There will be a difference in colors between the flutes and the very base of the shank. TiN coating is said to increase the life of an HSS drill bit by 6 times.

.

TiCN (Titanium Carbonitride)

TiCN coatings are even more wear resistant than TiN. Looking only at the flutes it may be hard to tell apart from solid carbide, but importantly there will be a difference in color between the flutes and the base of the shank. There should also be a bronze discoloration from the chemical reaction between the coated and uncoated portions of the shank.

.

TiAlN (Titanium Aluminum Nitride)

TiAlN will be a violet gray color and will be more resistant in high temperatures. There will be less of a chemical reaction between the coated & uncoated portions of the drill bit.

.

Black Oxide


Oxide coated drill bits will be black in color and have slightly longer life than HSS due to reduced friction. This may be difficult to identify as some uncoated HSS drill bits may also be black in color. They are technically not coated in black oxide, but heat treated. It is safer to advertise as uncoated if you are unsure.

.

.

Coolant Thru?

A drill bit may be coolant thru, allowing coolant to pass through the base of the shank and through the flutes in order to help control the temperature. This will be seen at the tip of the drill bit, where there will be holes that run through the entire bit and will connect to a hole the the back of the shank where to coolant enters. 

.

.

Type

Jobber Twist Drill Bit

This is the most common type and is seen many of the pictures above. It is identified as having about 8-12 times the flute length as the drilling diameter. This will look like about 3/4 of the OAL are flutes.

.

Screw Machine / Maintenance Length Twist Drill Bit


Machine drill bits (also called maintenance) will have a shorter flute length for increased rigidity and precision.

.

Counterbore Drill Bit


These drill bits will have a defined step between two drilling sizes. They must be center cutting on both steps and will produce to separate diameter holes with no taper between.

.

.

Drilling Diameter

The drilling diameter is often labeled on the shank, but can also be measured with handheld calipers. If the drill is one straight diameter, Be sure that you are measuring the outermost section on the flutes for the maximum diameter. Unlike many tooling measurements, drill bits may be sized in increments of 1/64ths so a precise measurement is needed. If no multiple of 1/64 is near your measurement, it may be a metric diameter.

.

.

Flute Length

As seen in the diagram at the top of the page, flute length is measured from where the shank ends (or the flutes begin) until the very end of the cutting edge of the bit.

.

.

Overall Length

The overall length is very simple; measure the distance between the farthest two points on the tool. This can be done with handheld calipers or even a tape measure as this does not need to be so precise.

.

.

Shank Diameter / MT #


The drill bit on the left has a straight shank diameter, while the drill bit on the right has a Morse Taper shank. Male Morse Tapers can be identified by their taper as well as the distinctive end which has two flat sections seen in the picture above.

Straight Shank diameters are often common sizes and can usually be measured by calipers. Very often will drill bits, the straight shank is the same diameter as the drilling diameter. Morse taper sizes are measured on the large end (the largest diameter on the portion of shank that tapers) with calipers or labeled, corresponding with the chart below: