Long Series Drills

Also referred to as twist or jobber drills, long series drill bits have long been a staple of a well-stocked toolkit. Available as single bits or as a long series drill set, they are often made from high-speed steel or high-speed cobalt and are coated for prolonged product life.

However, their length can work against them somewhat, with the tasks in which they're used expounding the problem of breakages. Long series drill bits aren't as rigid as their shorter counterparts, and if not held straight they can wander and break. In these cases, a centre punch can help to keep you on track, and to prevent drilling too deeply, a depth stop is an ideal accessory to keep those hole depths accurate.

Cromwell is proud to stock a wide choice of long series drill bits from reliable brands like Guhring®, Dormer® and our own brand, Sherwood®.

When are long drill bits used?

Long series drill bits are used specifically for adding depth to a hole or drilling in a space that's difficult to reach. Used by builders and electricians to cut through walls and ceilings to thread cables, long drill bits have their set place in a trade toolkit.

Long drill bit types

Long series drill bits are differentiated according to the material they're made from. The two most commonly found are HSS (high-speed steel) and HSCO (high-speed cobalt).

There are, however, a wide choice of finishes or surface treatments available, (outlined below) which offer various benefits according to the job type. All types of long series drill bits must conform to BS 328-1:1993 standard.

• Blue oxide   -   Protects against corrosion

• Black oxide   -   Adds a thickness to steel and protects against corrosion and friction

• Titanium Nitride   -   (TiN) resists wear and reduces friction for a prolonged tool life

• Titanium Aluminium Nitride   -   (TiAN) high hardness finish for cutting harder materials and alloys

• Titanium Carbon Nitride   -   (TiCN) is suitable for cutting harder materials and high and low alloys

• Bright   -   Uncoated and ideal for drilling wood, PVC and soft metals

Considerations when choosing a long drill bit

Material - it's important that you use the right tool for the right job. Choose your drill bit according to the material you'll be drilling into to ensure the best results.

Length- Choose the length of your drill bit or set it according to the depth of the holes you'll be needing.

Precision - Some drill bits give cleaner results than others. Decide on the finish you want before committing to a product.

Long series sets - A collection of long series drills contained in a storage case.

Long drill bit jargon buster

There are lots of technical terms used when describing a jobber drill. We want to make it easy for you to find just what you're looking for, so we've put together a list of definitions of the most common terms.

• Parabolic - a flute shape that enables efficient chip removal to allow greater drilling depths in one pass

• Morse taper - is a bit mounting shape that allows for secure mounting onto the spindle of a driver

• Threaded shank - this type of drill bit works in conjunction with a threaded adapter on a handheld drill

• Weldon shank - a drill bit with flat edges on the shank to ensure a secure hold

• Ball nose - mainly used for die sinking, this type of drill bit features a rounded tip

• Slot drills - where the tip of a drill bit appears flat, with two cutting edges on either side

• Spur - the centralised tip of the drill bit


Can I protect my HSS long series drill bit from breaking?

To a point, yes, regular maintenance helps to prolong the life of any tool. Keep long drill bits clean, store them properly and try using cutting oil on metal surfaces to smooth the way.

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