In no time, you can restore dull brad point and Forstner-style bits so that they'll drill clean, precise holes faster than ever.
When it comes to drilling accurate holes, I wouldn't give up mv brad point and Forstner bits. The problem is they don't stay sharp forever. But the good news is it only take a few minutes to restore them.
Unlike twist bits, which can be sharpened on a ^ grinder, you'll need to sharpen brad point and Forstner bits by hand. But don't worry, the process is pretty straightforward and easy to master.
DIAMOND FlltS. One way to make the task even easier is to use the right tools. 1 find that diamond needle files cut fast and smooth. What makes them better than ordinary needle files is that these files have industrial diamonds embedded in the steel blade instead of cut teeth. The hard diamond particles stay sharp for a long time and won't clog with filings.
All you really need are three files — flat, half-round, and triangular — for sharpening bits. To find out where to get them, turn to sources on page 48. Once you have the files, you're ready to get started.
Forstner bits are perfect for drilling flat-bottomed holes. But a dull bit causes the rim to overheat, which can draw the temper out of the steel. Getting a Forstner bit back into shape involves two steps — first honing the cutting bevel and then the rim.
BEVEL Before you can start filing, you need a way to hold the bit securely. To do this, I cut a V-groove in a block of wood and clamped the bit between this block and a small flat piece of wood in a machinist's vise.
Now you can begin filing. In the middle photo at *=-left, you'll notice there's a notch in the rim just behind the bevel. This provides clearance for the file. You want to tilt the file to match the established angle and take just enough strokes to create a clean, sharp edge.
A grooved block holds the bit securely. The top is beveled to guide the file for sharpening.
To sharpen the cutting ■ lips of a Forstner bit, stroke across the bevel with a flat diamond file. Be sure to take the same number of strokes on each cutting face.
Hone the rim of the bit with a round edge file. Draw the file along the curve of the rim to sharpen the edge. Again, use the same number of strokes on each side.
When filing the bevel, I count the number of strokes I make. This way, when I file the other bevel, I use the same number of strokes. This will keep the bit balanced and cutting smoothly, file the ramp. Before moving on to the rim, file a few strokes along the ramp on the other side of the bevel. This will remove any burrs that develop while sharpening.
finally, the rim. The second step is to sharpen the outer rim. You can see how to do this in the lower photo on the opposite page.
To hone this edge, 1 pick up a half-round file. Since there isn't clearance to file across the edge, I draw the file along the inside edge of the rim in a sweeping motion. After a few strokes, you should be able to feel a sharp edge forming.
Not all Forstner-style bits have a smooth, continuous rim. To learn how to sharpen these "multi-spur" bits, take a look at the box below.
Forstner bits are great for drilling larger holes, but for drilling clean small holes, a brad point bit does the trick. The technique for sharpening these bits depends on the type of brad point bit you have.
You see, there are two basic types of bit. Newer types of brad point bits blend the spurs and lips into a W-shaped tip (main photo on the opposite page). Traditional brad point bits have flat cutting lips and distinct outside spurs.
beveuo slocks, Tire key to getting these bits razor sharp is guiding the file to match the cutting angle that matches the bit angle on the bits. To do this, I cut an angle on one end of the V-block I use to hold the bits.
For new-style bits, you'll need to cut a compound angle. 1 tilted the blade on the table saw to match the bevel angle on the bit (my bit measured 75°). Then 1 set the miter gauge for the angle from the centerpoint to the tip of the spur (10s).
The main photo on the opposite page shows the setup for filing. The block is positioned just below the tip of the bit, The idea is to hold the file parallel to the top of the block.
filing. Now, file across the cutting edge of the bit. You'll know the edge is sharp when it turns from dull gray to bright silver. And as before, take the same number of strokes on each bevel.
traditional-styli bits. The process for sharpening a traditional brad point bit is a little different. For this type of bit, your guide block only needs to match the bevel angle on the cutting lips (upper photo).
After filing the lips, the last step is to hone the inside edge of the spurs. It'll only take a few strokes to put on a fresh edge, as shown in the lower photo. ES
After honing the lips, use a triangular file to sharpen the back edge of each tooth. This shapes the tooth and helps clear chips.
Next, sharpen the face of each tooth. Angle the file to match the factory grind. Then take even strokes for a smooth cut.
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