Annular cutter

As an annular cutter cuts only on the periphery of the hole to be made, it has to remove much less material as compared to conventional drill bits which cut and remove the complete material of the hole. Annular cutters are considered to be 3 to 4 times faster than conventional drill bits. Also while using a twist drill bit or metal hole saw one has to do pre-drilling and step-drilling operations for bigger diameter holes, whereas an annular cutter requires no pre-drilling and step-drilling. It is a one-shot drilling operation.

The annular cutters have fewer teeth and less wear, therefore with an annular cutter holes can be made at higher or faster cutting speed and a faster feed rate of the drilling machine.[5]

Because annular cutters do not have to drill/cut through the complete work piece, they require less thrust and thus less energy to drill through material.[6]

The hole made using an annular cutter is more finished, precise and accurate.[6]

Due to the unique geometry of the annular cutters, making holes at awkward angles is also very easy.[6]

The cooling of annular cutters is internal. The internal lubrication is provided through a hole with the help of a pilot pin. Internal lubrication makes the annular cutter faster and more efficient for deep hole drilling.[6]

As the annular cutters require very low RPM (from min 50 RPM), these cutters can be easily used with light duty drilling machines or portable magnetic base drilling machines.[6]

Annular cutters biggest advantage is the variety of sizes. Annular cutters start from 12 mm diameter up to 150 mm diameter and more if required. Various cutting depth (length) of annular cutters can be sourced depending upon the requirement.[6]

HSS annular cutter can be easily re-sharpened on a grinding machine and can be re-used for drilling. Re-grinding can be done until the desired cutting length is available on the annular cutter.[6][5]

HSS core drills are made from high-speed steel material. These are most popular core drills or annular cutters in market. HSS core drills are cheaper for smaller diameter i.e. 40 mm. The biggest advantage of HSS core drill is its ability to re-sharpen. Unlike TCT core drills, HSS core drills re-sharpened and used with good efficiency until the desirable length is remaining. HSS core drills have longer service life, high heat resistance: the characteristics of HSS core drills is that drilling with these core drills can be done without the use of excessive force.

The HSS Standard core drills are made from M2 steel. These core drills are one of the most popular core drills in western countries due to its cost and resharpening advantage. The Standard HSS core drills are used to drill Mild and Structural steel, Aluminium, Stainless steel of lower BHN., etc.

The HSS Cobalt are core drills made from M42 Steel. These core drills have 8% Cobalt in HSS. These core drills are harder than the Standard HSS core drills which gives better performance to drill harder material. A high percentage of Cobalt in HSS makes it faster, stronger and durable.[9] Cobalt HSS core drills are used to drill materials like Structural Steel, Stainless Steel, Cast iron, etc.

The HSS core drills with Hard Coating are core drills with a coating on it, generally TiN Coating. This make the core drills more resistant to heat, longer tool life and even removal of chips. These core drills are gaining lot of popularity over the Standard HSS core drills these days. These core drills are used Structural steel, Stainless steel, etc.[7]

Tungsten carbide tipped (TCT) core drills have tungsten carbide on their tips, a very hard material suitable for cutting through tougher materials. TCT core drills are more expensive than HSS core drills but are faster and more efficient making larger holes. TCT core drills are cheaper for bigger diameter i.e. above 41 mm. Tip breakage is more likely than with HSS core bits, and TCT bits may not be resharpened.

A Standard TCT core drill has tungsten carbide tips. These types of core drills are now available in vast range of diameter, for up to 150 mm. These are popularly used core drills on magnetic core drilling machines. These core drills are popularly used to drill materials like railway tracks, structural steel, stainless steel, cast iron, etc.

The TCT core drills with Hard Coating are core drills with a coating on it, generally TiN Coating. This make the core drills more resistant to heat, longer tool life and even removal of chips just like the advantage of HSS core drill. The biggest advantage of hard coated core drills is that these cutters are very good for cutting larger diameters on hard material. These core drills are popularly used to drill materials like corroded or weathered material, structural and stainless steel.

"Weldon shank" annular cutters have 2 flats and this is the traditional method adopted by many of the popular magnetic drill manufacturers. "Weldon shank" annular cutters fix in the chuck by tightening grub screws in the two flat areas.

"Universal shank" annular cutters has one flat and three quick connect grooves. This is also a popular method for using annular cutters into mag drills quickly, without any strain of tightening grub screws. mostly "universal shank cutters" can be used in "weldon -shank machines, where as weldon-shank annular cutters can't use in "one-touch" machines without the help of an extra adapter. while using "universal shank cutters" into "weldon shank" machines, the tightening area (flat area) is only one, which is also not 100% sufficient to tighten the both screws.

HSS core drills are cheaper than the TCT core drills for smaller diameters up to 40 mm, while TCT core drills are cheaper than HSS for diameters above 41 mm.

Once the HSS cutter loses its sharpness, it can be re-ground on a grinding machine and can be used again. While, re-grinding the TCT core drill is possible but very difficult and time consuming.

The chances of defect in TCT core drills is more because the tungsten carbide tips are glued on the core drill and when the core drill falls down or crashes on the material, the chances tip breakage is more. HSS cutter on the other hand are completely made out of one material.

TCT cutter biggest advantage is speed and ease in which it may cut harder materials. Especially for larger diameter TCT core drills are very successful. While HSS core drills are good when drilling not very hard material and for small diameter hole sizes.

The teeth on TCT core drills are harder than HSS, allowing them to cut more difficult materials.

The conventional twist drill has only two cutting edges, while an annular cutter or core drill has multiple cutting edges which helps to drill with much less horsepower and efforts.[12]

The conventional twist drill being solid and having only cutting point has to cut or remove the complete material of the hole to be made. While with annular cutters or core drills having multiple edges and being hollow cuts only on the periphery of the hole to be made.[5]

As core drill has to cut less material as compared to twist drill, the time required is also too less. A core drill is considered to be 3 to 4 times faster than twist drills.

A single core drill makes 5 to 10 times more holes then a twist drill, plus core drills can be again reground to make another 1500 holes, thus saving a lot of tool cost.

Unlike twist drills, core drills even for larger diameters do not require any pre-drilling or step-drilling.

Example: To make a 50 mm diameter hole with twist drill, one has to start making a pre-drilling of 10 mm, than 15 mm than 20 mm, ...up to 50 mm slowly increasing the size of holes. While with core drill one can drill directly 50 mm in one-shot.[12][5]

One of the biggest advantages of core drills over twist drill is burr-free holes and smooth holes, resulting in less scrap and wastage of material.[12][13]