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How to use an expansive bit?

Shop for Expansive bits

Image showing that expansive bits could be described as having similarities with both spade bits and auger bits Expansive bits are, in many ways, a cross between auger bits and spade bits in the way they work. Their spurs cut around the edge of a bore hole while their cutting lips prise material from inside, clearing the way for the bit to progress downwards.
DIYer working hard to get an expansive bit to bore a hole in a wooden workpiece One of the main differences is that expansive bits take a little bit of elbow grease to use effectively. For this reason, the method for using an expansive bit seeks to minimise the amount of necessary effort as far as possible.
Drilling a test hole with an expansive bit on a piece of scrap wood to test its accuracy If you are working on a project that relies on precision, it may be worth testing your drill bit’s accuracy first by drilling a few test holes.

For more information, see: What sizes of expansive bit are available?

Example of a hand brace, into which an expansive bit can be mounted

Step 1 – Attach bit to brace

With your expansive bit set to the width of your choice, secure it in the chuck of a large drill brace.

Image to advise DIYers to work slowly with their expansive bits

Step 2 – Bore slowly

Boring is a slow process… especially in this case! Working slowly means that you will find the bit resisting the wood less as you turn the brace, and therefore less force will be required.

DIYer turning over a workpiece after drilling far enough through with an expansive bit that the guide screw breaks the surface

Step 3 – Drill until guide screw breaks the surface

Continue drilling, checking the reverse side of the workpiece regularly to see when the guide screw breaks through. As soon as it does, remove the expansive bit and flip the workpiece over.

An illustration of tear out caused by a drill bit with a guide screw such as an expansive bit Stopping before the bit breaks fully through the workpiece prevents tear out that would be caused by the outrigger spur.
An electrician drilling through a wall, which could be done with an expansive bit If you are drilling through plasterboard and can’t access the other side, you can ignore this step and continue to drill until the hole is completed. As the reverse side of the plasterboard can’t be seen, tear out is not an issue.
Image showing an expansive bit boring a hole and leaving noticeable spur marks around the perimeter

Step 4 – Complete the hole

Insert the guide screw into the hole it originally made in the surface and complete boring the hole, remembering to continue drilling slowly.

What is the alternative to a drill brace

Image of a cordless drill driver, which can accommodate an expansive bit if it has a hexagonal shank You can also use expansive bits with electrically powered drivers.
Diagram showing how to use a cordless drill driver at a slow speed in order to avoid creating problems when boring with an expansive bit Use your drill driver at a slow speed if you are using an expansive bit to prevent the bit from digging into the workpiece and straining the motor, overheating or generally causing disaster! If you are using a drill press, you can manually set it to the lowest number of revolutions per minute. If you are using a cordless drill driver, you can use the speed setting, or apply only light pressure to the trigger, depending on the model you are using.