Shopping: Real Estate |  Costumes  |  Guitars
This Issue Archived Articles Blog About Us Contact Us

Sharpening Drill Bits

Making drilling holes easier

by Julian Edgar

Click on pics to view larger images

At a glance...

  • When to sharpen
  • Point and clearance angles
  • Grinding drill bits
  • Solving problems
  • Angles for different materials
Email a friend     Print article
This article was first published in 2008.

These days, bench grinders are so incredibly cheap that every home workshop should have one. As we covered in Using Bench Grinders, there’s a host of uses for a bench grinder, including grinding welds and shaping metal. But perhaps the greatest real-world use is sharpening drill bits.

Let’s take a look at how it’s done.

Easy, huh?

Firstly, don’t assume that because it looks easy, sharpening drill bits requires no skills and no practice. Sorry to tell you, but that is simply not true.

Especially when grinding small drill bits, it’s very easy to produce ‘cutting edges’ that in fact render the drill useless for any work at all!

However, once you know how to sharpen drills (and especially what to look out for when assessing how good a job you have done), it becomes much easier.

When to Sharpen

Clearly, sharpening of drill bits is normally carried out when they have become dulled. The signs of a dulled drill bit include the need for higher than normal pressure, the generation of excessive heat, squealing, and a lack of cutting progress.

However, drill bits might also need to be re-ground to suit different materials. As they are bought, drill bits have cutting surfaces that are configured for general-purpose work – drilling steel, for example. But for optimal results on materials like plastics, rubber or very hard materials, the drill geometry is best changed from the all-purpose shape. This can be easily achieved by grinding.

Good quality drill bits are expensive – very expensive in large sizes. But once you can competently sharpen drill bits with a bench grinder, you can buy lots of your drills secondhand, massively dropping the purchase prices.


At this stage I’d like you to go to the workshop or toolbox and grab a large drill bit – one that still has the ‘factory’ sharpness and end geometry. Don’t be shy – go off and get that drill!

Click for larger image

Hold the drill vertically and rotate it until it looks like this. Note the angles that the top edges of the drill bit form to the vertical – here, each face is at 59 degrees, giving an included angle of 118 degrees. This is a typical point angle for a general purpose drill bit.

Click for larger image

Here the point angle can be seen for a large (12.5mm) drill bit.

Click for larger image

Rotate the drill bit in your fingers until you can look at the ‘ramp’ behind one of the two cutting lips. If the drill bit is held vertically, the edge of the ramp forms an angle with the short axis of about 12 – 15 degrees. This is called the clearance angle.

Click for larger image

Here it is on the 12.5mm drill bit....

Click for larger image

...and here it is highlighted.


Before grinding a drill bit you must have very clear vision of what you are doing. This means the grinder must be brightly illuminated and, if you wear glasses for close-up work, you should have them on. The grinding wheel should be of fine grit and its face should be flat and square.

The first step in sharpening a drill bit is to grind the point angle.

Click for larger image

Stand slightly to the left of the grinding wheel, feet apart. Hold the drill about a quarter of the way along from the point, using the thumb and forefinger. Rest these fingers on the grinder’s tool rest. Use the other hand to hold the drill at its shank.

Click for larger image

Hold the drill so that it is horizontal but approaches the grinding wheel at an angle of about 60 degrees. Rotate the drill so that its cutting edge is parallel and close to the wheel. The drill can then be moved forward and the point ground.

The next step is to grind the lip clearance.

Click for larger image

Use the left hand to swing the shank of the drill downwards and to the left. These movements are only slight. Remember to keep the right hand supported by the tool rest. As you move your left hand, use your right hand fingers to roll the drill clockwise about a quarter-turn and simultaneously feed the drill forward against the grinding wheel.

Practice doing these motions with the drill you just brought in from your workbench. Use the edge of the desk as the 'pretend' grind stone.

Click for larger image

The sequence of motions is: left hand down and leftwards, right hand fingers rotate drill clockwise, both hands move drill forwards. Watch the cutting edge (red arrow) and you’ll see that as you do this, it moves forward and away from the grinding wheel. However, if you rotate the drill too far, or the left hand is not moved towards the left, the opposite side cutting lip (near to the point) will come into contact with the grinding stone – not what is wanted!

Click for larger image

When the point angle and lip clearance have been ground for one face, do the other. Make sure that the point angle is symmetrical and centred.

When grinding use only light pressure and frequently pause to let the airstream cool the drill bit.


When learning to sharpen drill bits, don’t sharpen a whole bunch of drills! Instead, sharpen one drill and then try it out on a piece of scrap steel, seeing how well it actually drills holes. To be honest, many of my first attempts at sharpening drill bits resulted in drills that were worse than before they were ‘sharpened’. So you must evaluate the results of your grinding before proceeding further.

  • Visual check

Click for larger image

A properly sharpened drill bit should have equal cutting angles, equal length cutting edges and equal angle lip clearances.

  • Test Hole

Click for larger image

Drill a hole through a scrap piece of steel. The drill should not chatter, squeal or stick, and shouldn’t need excessive pressure. The swarf (chips) should be continuous and produced in two lines, and the drill bit should be a tight fit in the drilled hole (ie remove the drill from the machine and try it back in the hole).

How Accurate?

A 1941 book I have on drilling and grinding makes the following statement:

While it is worthwhile acquiring the experience in grinding twist drills by hand, it should be noted that this would not be tolerated in any engineering works where accuracy is required: the drills would be properly ground in the tool room or proper drill-grinding equipment would be available.

Therefore, if really accurate holes need to be made (eg for a small diameter tap), it is best to buy a brand new drill bit for the job.


So what if you have sharpened your drill bit and then there are problems? The next stage is to consult this table:




Swarf emerges unevenly

Drill point appears to wobble, drill press shakes

Internal shoulder at base of blind hole

Oversize or rough hole

Off-centre point angle – unequal cutting lip length or angles


Slow penetration

Squeaking or squealing

Cutting edges dull

Lip clearance insufficient behind one lip


Drill grabs

Point angle too sharp

Lip clearance too great


Another way of finding problems is to again visually examine the drill-bit, looking especially at the clearance angles. As the following diagrams show, by looking at the drill-bit end-on, the actual clearance angles can be assessed.

Click for larger image
Click for larger image
Click for larger image

Back Cut

Click for larger image

It’s not mentioned in the textbooks but many large diameter drill bits have a sharply angled back cut behind the leading lip. In my experience, such a back cut can radically improve drill performance, so when sharpening large drill bits, don’t forget that these cuts can also be ground.

Different Materials

As we said earlier, if you move away from drilling typical materials like steel, a slightly changed drill bit specification is likely to give better results.

These diagrams show the variations – note that it is primarily point angle that is altered, so the grinding movement that gives the clearance angle is largely unchanged.

Click for larger image
Click for larger image
Click for larger image
Click for larger image


Sharp drill bits that have the right shape for the job speed up the work, allow holes to be drilled with greater accuracy, and are less likely to cause accidents. But when you begin sharpening drill bits, take it slowly and carefully, checking the performance of the drill bit and ensuring that correct grinding procedures are being followed. Then, when you have the knack, sharpen all the drills in your tool box!

Interested in home workshop projects and techniques? Youíre sure then to be interested in the Home Workshop Sourcebook, available now.

Did you enjoy this article?

Please consider supporting AutoSpeed with a small contribution. More Info...

Share this Article: 

More of our most popular articles.
An extraordinary aircraft

Special Features - 1 July, 2014

The Dornier Do X

From the weird to the weirder!

Special Features - 27 June, 2000

The GM Concept Cars

Japan's first supercar

Special Features - 8 February, 2008

Toyota 2000GT

The series conclusion

DIY Tech Features - 15 May, 2012

A New Home Workshop, Part 10

Tricks and tips for lightness with strength

DIY Tech Features - 24 March, 2009

Building Ultra Light-Weight Tubular Frame Vehicles, Part 2

We could be served up far better new cars

Special Features - 30 October, 2012

Three utter failings of current cars

Form beads in aluminium, steel and stainless steel intercooler plumbing

DIY Tech Features - 11 February, 2014

Make your own tube beader

Getting planning approval

DIY Tech Features - 7 February, 2012

A New Home Workshop, Part 3

Insulating the intake manifold from the head for more power

Technical Features - 4 June, 2008

Cool Stuff - Manifold Insulators

Avoiding damaging bangs

Technical Features - 21 August, 2012

Detonation and Pre-Ignition

Copyright © 1996-2020 Web Publications Pty Limited. All Rights ReservedRSS|Privacy policy|Advertise
Consulting Services: Magento Experts|Technologies : Magento Extensions|ReadytoShip