Drill bits are used for both wood and metal drilling purposes. Drill bits can be used when it is used long period. So sharpening a drill bit is a must. So many drill bits are available in the market. Among them, wood drill bits are the most available drill bits. This guide will help you to sharpen Twist bits, Spade bits, Brad Point bits, Spur bits, and Forstner bits. So let’s keep reading on!
Guide For Sharpening Drill Bits
Small, inexpensive bits should be discarded and replaced while dull. Larger, more costly bits should be sharpened. And though a professional sharpener can do the job for you, you can easily do the job yourself.
- To restore the cutting edges of twist and spade bits. Use a grinding wheel with a tool rest and a few simple accessories.
- A jig sets the correct angles for a twist bit, and a drill gauge checks the angles and lip lengths of the sharpened bit; a stop collar that sets a bit firmly against the tool rest enables you to grind the wings of a spade bit symmetrically.
- Always store your bits in partitioned boxes or canvas rolls, and clean them regularly to retard the dulling process.
- Fine sandpaper and an emery cloth will remove rust and wood sap. To clean the twist of a bit, dip a short length of manila rope in kerosene.
- Then in powdered pumice (available at drugstores). and wrap it around the flutes; to clean the screw point of an auger bit, use a piece of stiff paper
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Sharpening A Twist Bit
About Twist Bits
Two ridges called “lands” spiral around the central shaft, or web, of a twist bit. At the cutting end, the lands are ground to meet at an angle of 118° (82° on some special wood bits), forming two flats, called point surfaces, that converge along a center chisel edge.
The front edge of each point surface, called the cutting lip, is slightly higher than the back edge, or heel.
The clearance between the two allows the body of the bit to follow easily behind the lips as they cut away wood; the shavings move along the spirals of the lands and out of the hole.
The cutting lips are naturally the first parts of the bit to dull—the edges of the lips become slightly rounded, their clearance above the heels decreases and the bit binds and overheats.
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How To Sharpen Twist Bits?
- Step 01 – Holding the bit between the index finger and thumb of one hand, set it on the grinder’s tool rest and advance it toward the wheel until your index finger contacts the tool rest.
- Step 02 – Tilt the shaft of the bit down and to the left so that one of the cutting edges, or lips, is square to the wheel (above).
- Step 03 – Rotate the bit clockwise to grind the lip evenly.
- Step 04 – Periodically check the angle of the cutting edge, and try to maintain the angle at about 60°.
- Step 05 – Repeat for the second cutting edge. Wipe bits occasionally with oil to prevent rust.
- Step 06 – Use a T-bevel and a pencil to draw a line across the tool rest of the grinding wheel at an angle to the face of the wheel that is half of the correct angle for the bit tip—for most twist bits, set the T-bevel to 59°; for special wood bits, to 41°.
- Step 07 – To the left of this line, at’/4-inch intervals, lay out several parallel lines at an angle 12° less than the first—usually this will be a 47° angle.
- Step 08 – Use a C clamp to secure a small block of wood to the tool rest, at the right of and flush with the 59° line.
- Step 09 – For twist bits smaller than 1/8 inch, omit the parallel lines but adjust the tool rest so that the back edge is 12° lower than the front edge.
Grinding Twist Drill Bit
- Wearing safety goggles or a face mask, start the motor and let the grinding wheel run until it reaches a steady speed.
- Hold the shank of the twist bit in your right hand and use your left to position the bit against the guide block with one cutting lip perfectly horizontal.
- Slowly move the bit forward until it makes contact with the wheel, then simultaneously rotate the shank of the bit clockwise and swing the entire bit parallel to the 47° lines.
- Time the movements so that when the bit reaches the 47° position you have rolled from the cutting lip to the heel of a point surface.
- Position the bit with the other cutting lip horizontal and grind the second point surface in the same way. Alternate the passes between the point surfaces, grinding each equally until the bit is sharp.
- After every two or three passes, stop to cool the bit.
- Position a bit smaller than 1/8 inch in the same way, but do not swing or rotate the bit.
Set the bit in the lip corner of a drill gauge to compare the lengths of the cutting lips, then turn the bit slightly to check the clearance at the heels (inset). If the lips or clearances are unequal. regrind the bit.
Sharpening A Spade Bit
About Spade Bit
This flat-bladed bit has a point, or spur, that bites into the wood and steadies the bit on the center while winglike cutting lips chisel the hole.
The edges of the lips and the spur are beveled at an angle of 8°; on most spade bits the lips are perpendicular to the axis of the bit, but in some, they are set at an angle.
On a dull spade bit the bevels are slightly rounded and the cutting lips slightly unequal and out of line.
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How To Sharpen Spade Bit
- Step 01 – Set the tool rest at an angle of 8° to the horizontal, with the higher end facing the grinding wheel, and tighten a stop collar on the shank of a spade bit so that when the stop bears against the edge of the rest, the bit’s cutting lips will bear against the wheel face.
- Step 02 – Hold the bit flat on the tool rest and apply a cutting lip, bevel facing down, to the wheel face.
- Step 03 – When one lip has been ground, flip the bit to grind the other lip. To grind the bevels at the edges of the spur, swing the bit at about 90° and guide it against the wheel freehand (inset).
- Step 04 – Flip the bit to grind the opposite spur edge, taking care to grind both edges equally so that the spur remains centered.
- Step 05 – Remove burrs on the spurs and lips with one or two light strokes of a whetstone on the flat faces.
Filing Cutting Edge
- Secure the bit in a bench vise and use a smooth single-cut mill file to touch up the two cutting edges. File on the push stroke (above), tilting the handle down slightly to match the angle of the cutting edges; between 5° and 10° is typical.
- Then touch up the cutting edges on either side of the point the same way (inset), taking care not to alter its taper.
- Do not remove too much metal at the base of the point, as this will weaken the bit.
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Sharpening A Brad Point Bit
Filing Chip Lifters
- Clamp the bit upright in a bench vise and file the inside faces of the two chip lifters as you would those of a Forstner bit.
- For a brad-point bit, however, use a triangular needle file (right), honing until each cutting edge is sharp and each chip lifter is flat.
- Use the needle file to hone the inside faces of the bit’s two cutting spurs. Hold the tool with both hands and file towards the brad-point until each spur is sharp (right).
Multi Spurs Bits
- Secure the bit upright in a bench vise and use a triangular file to hone the leading edge, or face, of each spur (above). File with each push stroke, towards the bit’s brad point, tilting the handle of the file down slightly.
- Then file the trailing edge, or back, of each spur the same way.
- File all the spurs by the same amount so that they remain at the same height. Make sure you do not over-file the cutting spurs; they are designed to be 1/32 inch longer than the chip lifters.
Sharpening Fortner Bits
Inside Bevel Sharpening
- To touch up a Forstner bit, true the top edge of the bit’s rim with a file, removing any nicks.
- If the beveled edges of the cutting spurs inside the rim are uneven, grind them using an electric drill fitted with a rotary grinding attachment.
- Secure the bit in a bench vise as shown and grind the edges until they are all uniform (right).
Chip Lifters Sharpening
- Use a single-cut mill file to lightly file the inside faces of the cutters.
- Hold the file flat against one of the cutters—also known as chip lifters—and make a few strokes along the surface (above).
- Repeat with the other cutter. Finish the job by honing the beveled edges inside the rim with a slipstone.