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Twist Drills 101

by Jenny Mae Talaver January 13, 2020

Twist Drills 101

Do you work in the construction or home improvement industry? Are you a DIY renovator or woodworker? If you say yes to any of those two questions, then you need to learn about twist drills. Little as they may be, they are very crucial in any workman’s trade.

We at Rock Hard Toolz present you this comprehensive guide on Twist Drills to help you get started on mastering all tools for masonry and carpentry.

What are twist drills?

Twist drills

Twist drills are also known as twist bits. They are the most common drill bits used by workmen. They cut everything from wood to concrete. But most use them for cutting metals. They are made with M2 high-speed steel, tough enough to cut through all material you need to work on.

Twist drills are designed with two cutting edges and two to four flutes which are grooves formed in the body to provide cutting lips, to enable the removal of chips and to allow coolant or cutting fluid to reach the cutting action. You can get most cheaply in the widest selection of sizes among all drill bits.

How do twist drills work?

Twist drills cut round holes quickly and accurately in all materials. They get their name from the the helical flutes or grooves that wind around the body from the point to the neck of the drill. These flutes give a twist-like shape to the drill bit. They are built to withstand the high torque of turning, the downward pressure on the drill, and the high heat generated by friction.

To understand how twist drills work, let’s discuss their basic features and parts.

First: The point angle is located on the head of the twist drill. The angle is measured between the two main cutting edges at the top. A point angle is necessary to center the twist drill in the material. This point angle is disproportionate to the length of the main cutting edges.

Next: The twist drill always has two main cutting edges connected by a cut chisel edge. These drill the material. The length of these cutting edges determine the cutting performance of your twist drill.

Another essential feature of twist drills is the cut chisel edge. Located in the middle of the drill tip, it connects the two main cutting edges. has no cutting effect. This enters the material and exerts pressure and friction on the material.

To reduce the impact of the cut chisel edge, there is the point thinning feature at the top of the twist drill. The thinning centers the material and improves the tapping. This feature is standardised in DIN 1412 shapes, with the most common being the helical point (shape N) and split point (shape C).

Another essential feature is the helix angle (spiral angle). Otherwise known as the spiral angle, this feature guides the formation of chips in the material. The size of helix angles is disproportionate to the hardness of the material and length of chips it could remove in it. In addition to that, the smaller the helix angle, the longer the spiral of the twist drill.

Twist drills are perfect when you want a very accurate diameter hole. Say you want a press fit for a 3/16″ (.1875″ DIA) steel pin in a cabinet you are building. A #13 drill makes a .185 DIA hole, giving you a .0025 press fit for the pin. When desiring a very accurate hole it is best to drill 1/64″ undersize, and then make the final drilling with a new, or freshly sharpened, drill of the desired diameter. If drilling a large hole this could entail three drillings: drilling 1/4″ to expedite the quick sinking of the larger hole you desire, drilling 1/64″ undersize and final drilling of the desired size.

The next step to learning about twist drills is to learn about the different types of this tool and which one fits the material you want to work on.

Types of Twist Drills

Twist drills are commonly known in two types: high-speed steel drills, and carbide-tipped drills. High-speed steel twist drills are used most often for field and maintenance shop work. On the other hand, carbide-tipped metal drills get used in heavy production processes in a numerically controlled drilling machine. Other types of drills available are: carbide tipped masonry drills, solid carbide drills, TiN coated drills, parabolic drills and split point drills.

You can also differentiate them in terms of the shape of the shank. Straight shank twist drills are usually l/2-inch or smaller and into geared drill chucks. Secondly, there are tapered shank drills for the larger drills that need more strength which is provided by the taper socket chucks.

If you are buying a twist drill, remember that they range from 0.0135 (wire gage size No. 80) to 3.500 inches in diameter. Based on size, you can buy them as wire gage numbered drills, letter drills, fractional drills, or metric drills. Most common in workmen are wire gage twist drills and letter twist drills for drilling holes for tapping. You can get wire gage twist drills from No 80 (0.0135 inch) to No 1 (0.2280 inch). On the other hand, letter size twist drills range from A (0.234 inch) to Z (0.413 inch).

Fractional drills range from 1/64 to 1 3/4 inches in l/64-inch units; from 1/32 to 2 1/4 inches in 1/32-inch units, and from 1/1 6 to 3 1/2 inches in 1/16-inch units. Lastly metric twist drills come in three categories: miniature set, straight shank, and taper shank. Miniature metric drill sets range from 0.04 mm to 0.99 mm in units of 0.01 mm. Straight shank metric drills range from 0.05 mm to 20.0 mm in units from 0.02 mm to 0.05 mm depending on the size of the drill. Taper shank: drills range in size from 8 mm to 80 mm in units from 0.01 mm to 0.05 mm depending on the size of the drill.

Aside from determining the twist drill you will use based on its size and design, there are other factors to consider before you stock your toolkit with them.

How to choose the right twist drill?

The first step to choosing the right twist drill is considering the material you work on. For instance, are you drilling concrete? Choose carbide-tipped twist drills.

Next, determine the length of time you will use the drill. Certain coatings such as titanium make the bit resistant to corrosion. Thereby, making it good for specialty drilling.

Lastly, think of the type of drilling you will work on and on what temperatures the work will be conducted. You need to choose the twist drill based on the coating which can withstand a range of heat.

Conclusion

Twist drills are essential little bits in any workman’s toolkit. They drill holes in any surface or material you work on, depending on the type, size, finish and coating of the twist bit. But they are just one of the must haves for any DIYer or professional in construction or home improvement.

To know more about the tools and trade of masonry, go to Rockhard Tools. We offer you everything from product reviews to how-to guides. Rockhard Tools provides top quality masonry drill bits, jobber twist drill bits, anchors and fastening systems, hacksaw blades, jig saw blades and more.   

Jenny Mae Talaver
Jenny Mae Talaver



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