How to sharpen a spade bit

 
     
     
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 A selection of tools that can be used for sharpening spade bits, including a drill sharpening machine, bench grinder and mill file 

There are several methods that can be deployed when sharpening a spade bit, depending on the tools that you have available, whether or not your bit has spurs, and the material from which your bit is made.

 
     
 Image reminding DIYers to avoid removing material from the edges of a spade bit 

Whichever method you use, it's important to remember that you should never remove material from the outside edges of the spade bit, or you will risk changing its diameter.

 
     
   

Method 1 - Using a file

 
 Tool steel spade bits can be sharpened with a normal mill file, but high speed steel bits require a diamond file 

Tool steel spade bits can be sharpened with a file, but if your bit is made of HSS (high speed steel) then you will need to use a diamond file for it to have any effect. If your bit has spurs, you will need to choose a file that will fit between centre point and spur - a flat Swiss file or an auger bit file should do the trick. (See Files.)

 
     
 Diagram showing that the mill file must be angled to match the bevel of the spade bit's lip 

Step 1 - Sharpen lips

Lay your file so that it's flat against the bevelled (angled) edge on one of the lips of your spade bit. Keeping the file at the same angle, sharpen it. Three or four strokes with the file should be enough. Rotate your bit 180 degrees and repeat this process with the other lip.

 
     
   Wonkee Donkee warns what might happen if the shape of the drill bit is altered 
     
 Diagram showing how the file fits between the centre point and spur on a spade bit 

If you use a file with a rectangular cross section then you will be able to sharpen the lip of your spade bit without touching the spur or centre point. This means you can avoid any accidental damage.

 
     
 Direction to sharpen the centre point of your spade bit with a mill file 

Step 2 - Sharpen centre point

One edge on each side of the triangular centre point of your spade bit should have a bevelled edge. Matching the angle of your file to the angle of this bevel, sharpen the cutting edge of the centre point, then repeat this process for the corresponding edge on the other side of the bit.

 
     
 Image showing the part of the spade bit's spurs that should be sharpened 

Step 3 - Sharpen spurs

If your spade bit has spurs, the inside edges of these should now be sharpened, once again matching the angle of your file to the angle of the bevel on each one.

 
     
 Image to illustrate how spurs on a spade bit can get stuck and grab a workpiece if they are kept too sharp 

The spurs should not need to be sharpened as often as the other parts of the bit. If they are razor sharp, there is a strong chance that they will 'grab' the workpiece. This means that they will become stuck, and cause the workpiece to try to spin free of the clamp.

 
     
   

Method 2 - Using a bench grinder

 
 Diagram showing the location of the spurs on a spade bit 

This method can be difficult if your bit has spurs, as the wheel on your bench grinder is likely to be too wide to sharpen the lip without grinding off the spur in the process.

 
     
 An example of a spade bit with no spurs 

Grinding off the spurs will not render your bit useless, although it will make it bore rougher holes. Deciding whether or not to use this method will depend on whether you will be using your spade bits on a project where neatness is important.

 
     
 Diagram showing how a bit can be ground to include an acute angle at the end of each lip that will work similarly to a spur 

If your spurs do become a casualty, you can adjust the angle of your bit against the grinding wheel, shortening the centre point, but grinding the bit's edges so that they slope towards the centre. This will allow your bit to cut almost as neatly as if it had spurs. However, you'll need to be careful to make sure that you don't grind your centre point off centre.

 
     
 A grinding wheel set at the correct angle to sharpen a spade bit without altering the bevel 

Step 1 - Grind off spurs and sharpen lips

Adjust the tool rest on your grinder (the piece of metal in front of the grinding wheel) so that it matches the bevel on the side of the spade bit you're going to be sharpening. Grind off the spurs until you can touch the lip of the bit against the wheel a few times.

 
     
 DIYer grinding the centre point of their spade bit sharp 

Step 2 - Sharpen centre point

Paying attention to the bevel on the edge of the centre point, and trying to match it, sharpen your centre point with a few touches against the grinding wheel.

 
     
 A green light to show that it's OK to use brad point bits at high speed in softwood 

Your bit is now ready to go!

 
     
   

Method 3 - Using a drill sharpening machine

 
 Image of a drill sharpening tool, which can be used to sharpen spade bits 

Some automatic drill bit sharpening machines include a function for sharpening spade bits.

 
     
 A drill sharpening machine does all of the hard work of sharpening the drill while you wait 

This is the quickest and easiest way to sharpen your spade bits, although more expensive than using a file. The machine will come with instructions that will guide you through the sharpening process, although this usually involves inserting the bit, activating the machine and then watching as the hard work is done for you!

 
     
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