About Darex
Technical FAQ
Why Sharpen


Technical FAQ's 

Why does the sharpening tube move?  Is it supposed to move? 

The sharpening tube is a critical part of the sharpening mechanism and helps insure that you will not have negative relief when you sharpen.  You do not want to influence the sharpening tube, either up or down.  While sharpening and rotating the chuck in the sharpening port, apply light pressure straight into the port, along the axis of the port. 


The sharpening tube should have a stiff spring action to it.  The bump located on the top of the sharpening tube is the upper cam-follower.  The sharpening tube fits into the compound, which is the black plastic around the sharpening port.  Located on the lower portion of the compound is a large lip containing the lower cam-follower.  The chuck has a cam-liplocated on the base of the chuck body, containing a swing-cam adjoining it.  As the chuck is rotated clockwise in the sharpening tube, the swing-camrests on the lower cam-followerusing the follower as a guide to swing the drill bit into the sharpening wheel.  The upper cam-followeris moving in and out as it follows the cam-lip, allowing the drill bit to move toward the sharpening wheel at precisely the right time to remove material gradually, from the cutting edge to the trailing edge.  This movement and gradual in-feed creates the radial grind needed for a drill bit. 

return to top of page

I sharpened my drill bit, but it doesn't seem to cut very well. Why is the trailing edge of the bit higher than the cutting edge? 

You are probably experiencing the most common problem arising from drill bit sharpening; a condition called negative relief.  This occurs when the material taken off the trailing edge of the bit surface (also called the heel), is insufficient, and the trailing edge is at the same level or higher than the cutting edge.  The sharpening wheel creates a flat cutting surface on the point of the bit, but this must be "trimmed" in order for the cutting surface on the bit to work correctly. 

Negative relief can be caused by a defective sharpening tube, the type of drill bit being sharpened (see the next FAQ), a dirty chuck (see 2nd FAQ following this one), or by incorrect technique. 

The Drill Doctor is designed to automatically take the correct amount of material off the heel of the bit, for a perfectly sharpened bit every time.  Try sharpening again.  Loosen the chuck and re-align the bit.  If you haven't already, be sure you watch the video that came with your Drill Doctor. Also, make sure you are applying equal pressure throughout the rotation of the chuck, especially on the low spots on the cam, so that the chuck stays in contact with all cam follower surfaces as it is rotated in Port #3. 

It is also possible that the sharpening tube on your Drill Doctor is not working properly.  The sharpening tube is the black plastic tube in which you rotate the chuck while sharpening in Port #3.  Locate the bump at the top of the sharpening tube, and try pressing in on it.  This is the upper cam follower and should have a stiff spring action to it. 

return to top of page

What should I know about sharpening specialty drill bits?
Slow Spiral Raised Margin
Raised Margin
Fast Spiral

First, visually check for the alignment, without sharpening the bit. 

Align a bit in the chuck for a standard 118° drill bit.  Hold the chuck with the drill bit in it.  Notice the two flats on the chuck (see diagram below). Draw an imaginary line from the middle of the flat up into the drill bit.  The line should end up on the heel of the drill bit.  This procedure will hold true for drill bit diameters of 3/32" through ½ inch. 

If the line does not intersect the heel, then the alignment tube must be adjusted.  Should the line fall to the right of the heel, move the alignment tube #1, slightly below the standard setting.  If the alignment setting is moved too far, then the chisel point will turn diagonally, from cutting edge to cutting edge.  If the line falls to the left of the heel, move the alignment tube #1 slightly above the standard setting.  Check the alignment again and adjust accordingly. 

Raised Chuck

return to top of page

The bit seems to "back up"into the chuck as I sharpen - the chuck doesn't hold it firmly. 

Try this: Insert a drill bit into the chuck and tighten it as you normally would.  Now holding only the chuck, press the tip of the drill bit against a hard surface, like a piece of scrap wood on your workbench.  Apply about 25 lbs. of pressure.  Does the drill bit slide back into the chuck under pressure? 

If so, this is probably due to a build-up of sharpening dust inside the chuck.  Unscrew the chuck body from the chuck knob.  Using compressed air, a small brush or rag, remove all sharpening dust particles from the chuck knob pusher and jaws (the pusher is the piece holding the jaws and springs).  Now reinstall the chuck body onto the knob.  As you reassemble, make sure that the chuck jaws are in the jaw grooves, and that the jaws stay straight as the chuck body is threaded back onto the knob. 

return to top of page

How many times should I turn the chuck while sharpening? 

This depends on the diameter of the bit you are sharpening. 

It is crucial that you turn the chuck in Port #3 an even number of times to ensure that the bit is sharpened evenly. If you turn the chuck an odd number of times, the bit will not be evenly sharpened.  One turn means turning the chuck 180° It takes two turns for the entire drill bit to contact the sharpening surface once. 

Use this chart to determine the number of turns for various sizes of drill bits:
Bit Size 
Number of Turns 
    ¾" 50 or 60 
36 or 40 
16 or 20 
    ¼"  8 or 10 
2 or 4 

return to top of page

How hard should I push the chuck in while sharpening? 

Use a light and consistent pressure. Be sure to apply this light pressure when the chuck is in the lower part of the cam.  Keep all cam follower surfaces in contact. 

return to top of page

What is the difference between the 118° and the 135° sharpening angle? Which angle should I use? 

The 118° standard (non-split) general-purpose high-speed drills are used for drilling soft or mild materials such as cold rolled steel, aluminum, and wood.  A 118° drill point provides good results, but may cause"walking" at the drill point.  Commonly, a pilot hole is drilled before using a standard drill bit. 

The 135° split-point, heavy-duty, high-speed steel drills feature a heavy web construction for extra rigidity.  Use this angle with hard steels, stainless steel, titanium and other hard materials.  The 135°split-point eliminates "walking" and reduces thrust.  It also produces smaller chips that won't clog up the hole.  Ideal for hand and portable drills where bushings can't be used.  There is no need to pre-drill a pilot hole with the use of a 135°split-point drill bit. 

return to top of page

Why would I want to use a split-point bit, and how do I split the point? 

Splitting the point gives you a drill bit that is self-centering.  You split the point right after you sharpen the bit. 

To split the point, align the drill bit on the split-point setting.  Sharpen as you normally would, but do not remove the bit from the chuck.  Next, align the flats on the chuck with the flats on the splitting tube, and insert the chuck into Port #4 (the split-port). Pivot the chuck into the sharpening wheel for a "one count" (one turn).  This splits half the point.  Now carefully pull the chuck out of the split-port, just enough to rotate it 180°, and pivot the chuck into the sharpening wheel again, to split the other half of the point. 

Now remove the chuck and inspect the point. Depending on the size of the drill bit, it may be necessary to repeat the splitting steps until the drill point is split to the middle. 

NOTE: It's usually better to grind off not enough, rather than too much.  If the drill point is over-split, leave the bit in the chuck and try re-sharpening the bit in the sharpening tube (Port #3) to correct the over-split.  If this doesn't work, you should realign the drill bit and resharpen. 

return to top of page

I can't seem to change the sharpening angle from 118° to 135°. The loop handle won't budge. 

We use a powerful spring in this mechanism to make sure the angle is accurate.  Unfortunately, this also makes it a little tough to change angles. Try this: insert the chuck, without a bit in it, into Port #3 (the sharpening port).  With one hand on the chuck for leverage, you should be able to pull out the loop handle with the other hand and change the setting. 

return to top of page

Why can't I sharpen a small diameter bit properly? 

Small diameter drill bits (1/4 inch or less) require a little more care in the alignment process.  With small diameter bits, the chuck jaws turn the bit as you tighten the chuck, thus misaligning the bit.  Set the alignment lever to desired setting (standard or split-point), align the drill bit and tighten the chuck knob.  Before going to port #3, view the chuck through the back (knob end), to ensure that the chuck jaws are all meeting the drill bit at a 90°angle.  If the jaws are wrapping around the bit, loosen chuck knob slightly, until jaws are straight. 

Also, too many rotations on small diameter bits will result in a negative rake angle.  For example, with a 3/32" bit, rotate the chuck 2 or 4 times; with a 1/8" bit, rotate the chuck 4 or 6 times; etc. 

return to top of page

Why is the drill bit not centered in the chuck? 

Prior to aligning the bit, the drill bit should have a "slip-fit" in the chuck.  With the drill bit in the chuck, turn the chuck knob clockwise (CW).  This will close the chuck jaws onto the drill bit. Turn the chuck knob until it stops then loosen the chuck jaws slightly by turning the chuck knob (CCW).  At this stage, the drill bit should have a "slip-fit" and will slide in or out and rotate freely within the chuck. 

return to top of page

Why is the point of my drill bit flat? 

First, check the chuck to ensure that the chuck jaws are in the jaw grooves.  Second, during the alignment process, the pawls may have been gripping "ON" the flutes of the drill bit.  Re-align the drill bit making sure that the pawls are located "IN" the narrowest section of the flutes. 

return to top of page

Why is the chisel point of my drill bit turning after I sharpen the bit? 

A turned chisel point indicates that the drill bit has not been sharpened enough (not continue to rotate chuck in sharpening port) or that the drill bit has too much relief.  Relief is the amount of clearance between the cutting edge and trailing edge of the drill bit.  To correct too much relief on the drill bit, you will need to make an adjustment in the alignment.  Example: If the alignment was set on the standard drill bit setting, move the alignment tube clockwise (CW), halfway between the standard and split-point setting.  Align the drill bit as usual and sharpen. 

return to top of page

Can I sharpen a broken drill bit? 

Yes, you can.  To prevent the sharpening wheel from wearing out prematurely, it is recommended that you use a bench grinder to put the basic shape back on the tip of the bit.  Then, use the Drill Doctor to finish and sharpen the drill bit. 

return to top of page

Century Distributors PO Box 54-195 Mana, Wellington, New Zealand
Ph: 0064 4 567 1405  Fax: 0064 4 567 1406