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Why would you choose an expansive bit over other drill bits?

Why would you choose an expansive bit over other drill bits?

Shop for Expansive bits

Example of an expansive drill bit The question in this case is more appropriately, “why would you choose an expansive bit over another set of drill bits?” as that is where the expansive bit’s real strength lies. Read on!


Image to show that owning an expansive bit can be as good as owning a set of other drill bits

Always be prepared

Expansive bits can be set to bore holes of a huge variety of widths, as small as 16mm (5/8“) and as large as 150mm (6”). This means that you would have less need to purchase other wood boring bits, unless you needed one that was smaller than 16mm (5/8“).

Image to show that buying an expansive bit can save money in comparison to buying a set of drill bits This saves the DIYer from having to buy a set of wood boring bits, and therefore saves both money and space.


An illustration of tear out caused by a drill bit with a guide screw such as an expansive bit


Due to the way the bit’s screw tip and spurs are constructed, there is likely to be tear out on exit. This means that, as the bit leaves the wood, it will tear through the wood fibres, creating unsightly splinters. However, this can be avoided by stopping drilling as soon as the guide screw breaks through the reverse side of the workpiece and completing the hole from the other side.

For a step-by-step guide, see: How to use an expansive bit?

Image showing that expansive bits can sometimes bore holes that are wider or narrower than intended


Even if the cutter is set to the right length on the measurement gauge as accurately as possible, it is not unheard of for expansive bits to cut slightly larger holes.

Image to illustrate that accuracy is a vital part of joinery While this is unlikely to cause a major problem in most woodworking projects, joinery relies on accuracy and large amounts of work can be ruined through drilling inaccurate holes.
DIYer having some problems getting an expansive bit to bore a hole smoothly

Not easy to control

Because of the asymmetric design of the expansive bit, with one long outrigger protruding from the centre with a much smaller primary cutter that is not always located opposite, it can be difficult to keep the bit moving. This can make for a jerky, undesirable experience thanks to the friction caused by dragging the outrigger spur and lip through the wood fibre, which can cause damage to the wood.

Image showing that you may have to spend some money on a screwdriver or socket wrench if you buy an expansive bit

Need tools for adjuster screw

Even though you save money on drill bits by buying a set, some of that money will have to go on buying a screwdriver or socket wrench so that the lock screw can be activated.

An image of a screwdriver, which is used to adjust an expansive bit and may be a necessary purchase unless you already own one Depending on whether or not you already have a screwdriver in your toolbox, this might influence your decision on whether or not to buy an expansive bit.
Wonkee Donkee advises DIYers to buy an expansive bit if they need to drill holes that will be concealed or do not need to be neat

Wonkee Donkee Tools