Introduction: How to Sharpen Used and Dull Drill Bits (By Hand!!)
Have you tried to drill something recently and noticed your bits aren't cutting like they used to? Maybe some of your bits are so bad, you can't even get through wood or soft metals anymore without creating a plume of smoke and high shrieking squeaks. Well before you head over to the hardware store to buy yourself a brand new box of drill bits, try this simple technique first and save yourself a lot of time and money!
Follow these steps and you can transform your used, dull, chipped, broken, or otherwise useless drill bit, into a prime hole blasting instrument.
Sharpening bits is a tricky task. When I started my job as a machinist nine years ago, my trainer was skeptical about using any kind of automatic machine or fixture to re-sharpen our drill bits. In fact, you’ll notice that most of those fixturing devices or machines cost a lot of money, and very rarely do they ever give you something close to a factory sharpen (unless of course you fork out enough to buy an industrial sharpener). So what’s going to be demonstrated here is a kind of lost art—sharpening by hand on a belt sander or bench grinder.
Now, I’m not saying that after this tutorial, you’ll be able to achieve a perfectly sharp drill bit, but it will get you through the next job until you get enough practice to really put an edge on your cutting tools. My trainer and I have gotten so good, in fact, that whenever we’re given those cheap HSS China bits (that pretty much everyone has in their garage), we’ll pull them right out of the box and sharpen them before their first use.
So without further adieu, here's what you’ll need:
- A dull or chipped drill bit
- A bench grinder or belt sander
WARNING! Your hands will be very close to the sharpening device, and dangerously at risk with losing some skin. DO NOT wear gloves as they can actually get caught into the sharpening device and pull you in. Be mindful and deliberate about where you position yourself on the sharpening device. And you should probably wear safety glasses too.
Step 1: Know Your Drill Bit
There are many features on a drill bit that can be defined. For speed sake, were only worried about 3 basic features on the bit: the lip, land, and chisel.
The "lip" is what does the actual cutting. The two lips on the twist drill should be symmetric if an equal cutting is to be done while drilling. If one lip is favored while sharpening, it will become bigger than the other and most of the cutting will be performed on one side of the bit. This is bad as it makes non-straight holes.
The "land" or "landing" is what follows the lip and will support the sharp edge while the bit is cutting. The landing must be angled in such a way that it leaves clearance between the part you are trying to drill and the lip. However, too much angle subtracts support from the lip, and will cause the bit to chip more often, especially on the corners.
The "chisel" is the line which is created when the landing from both sides of the twist drill intersect. In truth, this area does no cutting motion. Don't think of it as a true chisel. In fact, while the drill is turning and being forced down into your work-piece, the chisel smears the wood or metal you are drilling into the lips. For this reason, it is especially important to create a very small chisel.
Step 2: Uderstand Why Drills Chip and Dull
In order for you to know how to better sharpen your bit, you should know why you're even doing this.
Chipped bits are caused because the landing force behind them cant support the forces exerted by the drilling operation. So make sure your landing has a curved shape to it. Curved shapes add support to the lip.
Dull bits are caused when either the chisel is having trouble smearing the material to the lip and needs to be re-defined on the face of the bit. Or, the lip is rolling over and needs to be re-sharpened so that it pushes directly into the work-piece.
Step 3: Prepare Your Bit
Run a file across any burrs that bay be on the shank of the drill bit. If anything were to go wrong, and the bit were to slip in your fingers, you wouldn't want these nasty burrs cutting into your skin.
Step 4: Choose Your Sharpening Tool
Either a bench grinder or a belt sander will work for sharpening bits. Just make sure that the guards on either one of these machines is less than 1/8" away from the belt or wheel so that your bit doesn't get caught between the guard!
Step 5: Practice Holding the Bit
Start in a comfortable position with your hand against the machine support and take the drill bit into both hands. Hold the bit at a 60 degree angle to the face of the belt sander. Place the end of the landing so that it is directly against the belt. Use steps 5-7 to move the bit across the belt into the finish position. Notice in these two pictures how little difference there is between the start and finish sharpening positions. Steps 5-7 are simultaneous steps to get you to that finish position but notice how the only hand that moves is the left hand. The right hand stays stationary, with only the fingers guiding the drill bit.
Step 6: Cut the Landing
Cut the landing by raising the left hand while applying pressure to the sharpening device.
Step 7: Shape the Chisel
By moving the left hand towards the right, you will create the chisel angle. Practice a few times until the chisel angle is 45 degrees from the lip.
Step 8: Shape the Landing
By rotating or rolling the bit counter clockwise, you will create a rounded landing that gives more support to the lip.
Step 9: Combine Cutting, Shaping, and Rotating
Combine all three movements while sharpening to make the perfect cut on the drill face.
Repeat this step a couple of times and rotate the drill bit 180 degrees in your hand to sharpen the other lip.
WARNING: this procedure will heat up the drill bit face. Have a cup of cool water by your belt sander or bench grinder to dip the tip of the drill bit into to cool it off. If its too hot to handle, then you are probably weakening the integrity of the steel that your bit is made of. So keep it cool.
Step 10: Repetition
It may take a couple dozen times to get the two lips of the drill bit symmetric. That's normal and requires a lot of patience. But keep on trying! Often rotate which side of the bit you are working on so that you don't favor one side over the other. Always make deliberate cuts, don't try to "feather" a sharp tip by pressing the drill bit lightly into the sander or grinder. This almost always leads to uneven lips or will cause you to roll your lip so that it no longer cuts.
If you've practiced a little with your bit, and have been able to successfully roll and shape your landing and chisel, you are ready to start drilling! Go ahead and try out your bit in a drill press or hand drill. If drilling is still difficult , look at your chisel and landing angles to make sure you've got enough relief. If you see chips only coming off one side of the bit, make sure the two lips are symmetric across the center-line of the drill bit. If you see chips come off of the bit on both sides of the drill bit, your good to go!
Thank you for ready this how-to on sharpening your own bit!
Step 11: A Final Word
If you happened to have purchased these really nice cobalt chromium split drill bits, I've got some bad news for you. That split through the chisel has made drilling a lot nicer for you, but its very unlikely you'll get a good sharpen out of these bits by hand. You really need a machine that can go back and cut the relief on the back side of the landing to reduce your chisel size. Not relieving the chisel just makes too much smearing of the material during drilling and is practically impossible to get through most metals.