How to sharpen drill bits

September 24, 2009, 2:44 pm betterhomesgardens

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The most common drill bits used at home are twist, spade and masonry bits.


All of these bits go blunt as their cutting edge rounds over. Then they don't bore properly, and they get hot and smoky as they try to burn their way through the timber or metal. But instead of buying new bits for each new job - many cost over $10 - try sharpening them yourself. Here's how.

1. Filing spade bits The simplest bits to sharpen are spade bits. Mount the bit in a vice, with the flat, bevelled cutting edge sloping down towards you. File at an upward angle towards the edge equally on both sides. Do the same for the spur. After a few passes of the file, the bit will cut like new.

2. Grinding spade bits The same technique can be used on a bench grinder. Gently hold the bevelled cutting edge against the wheel to take a small amount off the surface. When using a bench grinder, avoid holding the bit against the wheel for a long time as it will heat up quickly and change colour. This means the steel has lost its temper and will blunt again quickly. Have a container of water handy to cool the bit.

3. Grinding twist bits The traditional and arguably the best way to sharpen twist bits is also with a bench grinder, but it does require practice. However, perseverance pays off because ultimately you will be much faster and the grinder is always there, ready to go. The trick is to copy the angle of the old machine-ground surface. As you grind, rotate the bit away from the edge to form a curved surface that leaves the cutting edge higher than the rest of the grind. Repeat for the other side, making sure both sides are even. As with the spade bit, keep the bit cool by frequently dipping it in water.

4. Sharpening machines There are several sharpening machines to help you keep your bits sharp. The entry level model is the Vanguard Drill Bit Sharpener at about $12. It fits onto your drill, and the bit is fed against a grinding wheel inside the unit. The next step up is the Multi Sharp Drill Sharpener, which is held in a vice and attached to a power drill. It has wheels for both steel and tungsten carbide masonry bits, and a guide to get the angles perfect. It is a little fiddly to get going but will sharpen twist, spade, dowel and masonry bits and costs $48.90. The most expensive unit, at $79, is the Ozito DIY Multi Function Sharpener, which is bench mounted and has its own motor. It features a clamping device for accurate setting of twist bits and also has chisel, plane, knife and scissor-sharpening functions.

5. Using the Multi Sharp Drill Sharpener Use the handy guide to clamp the drill into the holder, then feed the bit against the grinding wheel. Rotate drill holder between the stops to grind the point of the bit without going too far.

6. Using the Ozito DIY Multi Function Sharpener Fit the bit into the clamp, set the length and tighten. Start the machine and rotate the bit holder from side to side, using light finger pressure to sharpen the bit

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