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When to Choose and Use Long Drill Bits

When to Choose and Use Long Drill Bits

When to Choose and Use Long Drill Bits

It would help if you considered other dimensions besides diameter. Twist drill bits are the most effective tool for drilling wood, steel, and other non-ferrous metals because of their flat cutting edges and spiral flutes. Knowing the benefits and downsides of both short and long drill bits can help you choose the right drill bits.

Types of Long Drill Bits (Length)

1. Screw Machine-Length

These shorter bits, first designed for screw machines, are typically 4 to 10 times longer than their diameter (smaller sizes are proportionally longer). They can also be used in portable drills where there is a need for limited clearance and are known as "stub-length" bits.

They have the stiffness frequently required for drilling into more rigid metals and alloys thanks to their shorter flute and longer overall length. With less runout, skating, and deflection, rigidity keeps the holes straighter. Their primary flaw is that they can only drill as far as their flutes allow, which is 214 inches for a 12-inch bit.

2. Jobber-Length

A jobber length is a perfect option when considering the size of a drill bit. It's the most appropriate length for various applications, as they are short and long enough. They are the most commonly used parts in the workshop. Jobber drill bits are ideal for drilling into soft metals and wood. Jobber drills, which have lengths between 9 and 14 times their diameters, might be sufficient for all except the deepest holes.

3. Taper-Length

Conversely, jobber-length drills of the same diameter are shorter than taper-length drills. They can drill deeper holes because of their proportionally longer flutes, which are the same size as taper-shank bits, thus their name. Since they are compatible with standard chucks and collets, you can use them in place of taper shanks in many applications. 

This gives them an affordable alternative to expensive long drill bits. Speciality high-helix taper-length drills can be used on cast alloys and non-ferrous metals to help in chip evacuation because chips from deep holes have a considerable distance to go.

Read More: Auger Bit vs Spade Bit vs Hole Saw

4. Extra Long Bits

Extra-long or extra-long drill bits, which can reach up to 18 inches, are famous for drilling through or deeply into thick workpieces or accessing difficult-to-reach components in manufacturing, building, and maintenance applications. They are frequently necessary for boring channels for running wire or cable or drilling lengthwise into roof beams or building construction.

5. Aircraft Extension Bits

Extra-long drill bits with jobber-length flutes are known as aircraft extension bits. They are employed when reach rather than hole depth is required, like when attaching the extruded aluminum panels of a hollow aeroplane wing. You can get comparable results by connecting a shorter bit to a longer drill bit extension or extender.

Extra-long drill bits are typically available in smaller diameters to keep the needed rotational power low and minimize runout and imprecision since their length makes them less stiff and steady than shorter bits. Start the hole using a more straightforward bit for maximum results and to reduce breakage, then use the extra-long drill bit to extend the pilot hole to the required depth.

Read More: Spade bit vs Auger bit vs Forstner bit


It would help if you always used the shortest, stiffest drill bit capable of reaching the required drilling depth. If ultra-precision is unnecessary, your operation may use jobber bits rather than screw machine lengths. However, there is no replacement for extra-long drill bits when deep blind holes are needed. Get the best drill bit set for your drilling operation.
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