Despite their simple design, there are a few things to bear in mind when using spade bits for a woodworking project.
The first is that the central point is quite long, so you should never attempt to drill through a workpiece that is resting directly on your bench to avoid damaging it.
Make sure there is a spare piece of wood behind the one you are drilling through. Not only will this prevent damage to any of your workshop equipment, but it will also help to prevent tear out when your spade bit breaks through the reverse surface of your workpiece.
Step 1 – Marking up the workpiece
Make sure you have marked the central point of the hole you would like to drill, and that your workpiece is secured in a clamp or vice.
To make doubly sure that your drill bit stays on course, you can drill a pilot hole at the location of this mark with a 3mm (1/8″) twist bit. This is optional: the central point of your spade bit should be sharp enough that it will keep itself on course, but the pilot hole will give it a much better chance.
Step 2 – Set drilling speed
If you are using a drill driver with an adjustable speed setting, use the table below to help you determine which speed to set it to.
SPADE BIT SIZE (mm/”)
26-36mm (1 1/8-1 1/2″)
HARDWOOD SPEED, WITHOUT SPURS (rpm)
HARDWOOD SPEED, WITH SPURS (rpm)
SOFTWOOD SPEED, WITHOUT SPURS (rpm)
SOFTWOOD SPEED, WITH SPURS (rpm)
ACRYLIC SPEED, WITH SPURS ONLY (rpm)
While it is possible to use a spade bit with spurs to drill through acrylic, using a bit without spurs is not recommended.
Exceeding the recommended speed for acrylic could cause it to melt. Not applying enough pressure can do the same, as the bit may rub rather than cut. If you’re planning on drilling through acrylic with one of these bits for the first time, remember that practice makes perfect, so try boring through a spare piece of acrylic a few times first.
While 1000rpm and below may seem slow, it is still much quicker than the speed a bit would move in a hand-powered drill (which usually moves at less than 100rpm).
Step 3 – Drilling the hole
Put the tip of the drill on the mark you made, or into the pre-drilled pilot hole. If you are using a hand-held drill driver, make sure you are holding the bit square to the workpiece. You should be able to see if you’re going off square as you drill, so don’t be afraid to make adjustments if necessary.
Activate the drill and be prepared to hold it steady once it grips the wood. Spade bits generate much more torque than other wood-boring bits as they have more flat surface area to push against the wood, and it may feel as if the drill driver is trying to pull away from you. Don’t let it!
You may find that you need to apply more downward pressure than you might with other types of wood bit. This is normal, as no part of the spade bit is designed to draw it through the wood automatically (unless you are using a self-feeding spade bit – see: What are the different types of spade bit? ).
If the bit slows down and starts to stick, you are probably pushing down too hard, so release a little pressure.
If your workpiece is not clamped down, it will try to lift up once you make it all the way through and into the scrap wood behind. Lift the bit out of the hole and regularly check progress to see how far you have gone.
Step 4 – Avoiding tear out
While it may not be possible to completely avoid tear out with a spade bit, there are a few tricks you can try to make sure you get a neat exit hole if you have been unable to back your workpiece with scrap wood.
Slowing the drill bit down before it makes it all the way through the workpiece can help to minimise the amount of tear out.
Alternatively, you can stop drilling and flip the workpiece over as soon as the centre point breaks through the wood’s surface. You can then use the resulting hole as a pilot to locate your bit, and complete the hole from the other side.
Leaving the drill running at a slower speed as you withdraw it from the bore hole can also help to clean up the insides of the hole and any tear out as the sides of the bit have a second chance to scrape away any excess material. If you’re still left with a messy borehole after this, leave your drill bit running and insert and remove it again as many times as you need to leave a clean hole.