The AM Forum

We all use dull drill bits from time to time.

Twenty years ago I once pushed so hard on a drill
with a dull bit,  that the bit broke and then ripped into the
fleshy part between the thumb and index finger. I drilled
my own hand with a jagged bit!  What a nasty torn up cut.  
It took 10 stitches and lots of blood.

I recently learned how to sharpen drill bits effectively.  
I thought I knew how a few years ago, but it was hit and
miss. Now they come out FB.  It's such a joy to get an old
and favorite dull bit working like new!  Snapping a good bit
and repairing it like new is a rush. In the distant past, I used
to throw away the dull and broken bits not knowing any better.
All sizes can be repaied and sharpened.

I've been to machione shops where they've had 1" bits that
were sharpened so many times that they were 2" long stubs!  

No, I don't want to cop out and buy a $300 drill bit sharpener.
I notice the REAL men sharpen them by hand... :D

Anyway, are there any machinists, or guys who know the finer
details to sharpening bits on a sander or grinder?

Some of my questions would be:

1) Why do some have a flat cutting taper, while others have
a sharp angle at the tip?

2) Please describe what a proper taper should look like when
finished.

3) What are some of the techniques used?

4) etc, etc.

Please consider doing a two page article for beginners!

Thanks!

73,
Tom, K1JJ

Tom

You need to form an angle of  114° in the drill, you can doit easy with some practice, use a simple grinder, in the sharpen process turn the bit in a shorth half circle for each side. and keep the drill in a 5 to 6°, respect to the axis of the grinder.
for the right angle, you can use a gauge, ask in some good tool shop.

start with at least 1/4" drill, and keep on mind the way of the drills turns. the grinder stone must have a flat surface.

this angles works great for any metal or hard material
 and of course USE AN EYE PROTECTION!Regards!

Pedro

Unless you are drilling polycarbonate.  Then you want the bit dull.  If it isn't dull it then chuck it in a drill that has a very speed.  otherwise Pedro is correct.

Drill Doctor !!!

Easy, quick and accurate geometry everytime.
This is no infommercial. the thing really works.

Hey Tom,  Paul Harvey is always advertising the Drill Doctor on his news show and it's not anything near $300.  I've been contemplating buying one but will probably wait until I get a round tuit.  

The World Champion Procrastinator, Eric - WB2CAU

Is that some kind of drill sharpener?

Where do you find one and how much do they cost?

I once knew an old gentleman who could sharpen them by hand, just eyeballing it.  He told me it was so simple.  He tried to show me, but I never could get the hang of it.  Sometimes I could get them to come out right, but usually, even though they LOOKED ok, they wouldn't drill a hole in hot butter.

His technique involved putting the drill against a grinding wheel at a certain angle, and swinging it while rotating between his forefinger and thumb.

I once passed up what looked like a high quality sharpener (the thing looked complicated, with a lot of hinges and pivots, and appeared  to be from the 1920's) at a hamfest because the guy wanted a few bucks more for it than I was willing to pay.  I  have kicked myself ever since.

Yep, that's how it's done, Don.

I had a machinist show me once and then Bob/KBW did a few
weeks ago.

You roll it between your thumb and forefinger at a sharp angle
[like 114 degrees as Pedro says]  with the grinding wheel
against the direction of the bit. Just like when sharpening a
knife edge.  Do 1/2 turn and one side at a time.

It took me lots of tries to get the hang of it. As you said,
sometimes it looks good but sucks.  I found that the angle
needs to be sharper than you think.

Best way is to have a machinist show you and let you do a
few while he watches.  The big bits are easier than the small
bits. But even the small ones come out good with practice.

If the bit squeaks, it is dull.

I still wonder why some bits have a shallow taper while
others are sharp angled. ie, can a shallow tapered bit be
reground to be a sharp taper and still work? Is a shallow
taper for certain types of work?  What is the meaning of life?

BTW, I use a sander, not a grinding wheel. Seems to give
more control. It is a unit that sits on the table with a large 14"
~120? grit disk.

I understand the commercial drill bit sharpeners work well.
Maybe we can hear more about them.  


T

http://www.drilldr.com/

Vu ..... the thing that impressed me most was the ability to restore broken bits quickly. Once you get familiar with the collet workings you can resharpen a whole drill box in about 20 minutes. It even worked on my carbide masonry bits.

The drill doctors are on sale at Sears right now. How opportune....

Larry

As I interpret info from the web site, they sharpen 3/32" to 1/2" sizes, or 1/2" to 3/4" sizes, or both.  What about smaller sizes?  I normally use numbered drills rather than fractional inch sizes, and mostly #18 and smaller.  Will the drill doctor sharpen those smaller sizes?

Unfortunatly, for us visually impared Old Farts, that's it.... 3/32 "
It does do the number bits down to  #42. I did get a #43 thru it with ...... sufficient results.

Beyond that the cams that control the backoff angle would have to be modified or the cutting edge may not have sufficient strength. But once you get to #43 and up the work, most likely, will be in material where strength isn't the issue. Heat dissapation from the cutting edge becomes more a problem.

That Dr. Drill [HA!] video has a good demonstration of how
to do it manually, by hand, on a grinder.

Though, the Drill Meister looks worth the money.

For the smaller than 3/32" bits, just learn to do them by hand
and you're covered.  I did a few <1/8" ones the other day and
it takes literally seconds to sharpen once you get the hang of it.

Have a cup of water next to the grinder to quickly dip after each
pass. Otherwise they get red hot and will probably lose their temper.
[you don't  want a POed bit]

T

Yes, thats how I do it Don. It just takes a little practice. Its a bit easier with a belt sander because of the flat surface. Never tried a "Drill Doctor". Its a good skill for a the typical cheapskate ham (like me) to learn.  I will look at the "Doctor" website though and see what thats all about...........Larry

Sharpening Drill bits take alot of experience to get them to come out right.
Basically you need to use a fine wheel so the drill doesn't "bounce" all over the place. Rough wheel first to get the big chips, really dull point close to finish.
Some people make it look real easy, a proper point in a machine shop is important to get the proper size holes. Thats right, you can make the drill cut bigger if not done correctly or on purpose ;D
   Usually at home, as long as the drill cuts, thats good enough :D
The wheel needs to have a fairly sharp corner so you can "Thin out" the center web, if not, you cannot penetrate the metal with the point. Some drill have thicker webs then others.
I sharpened 1000's of drills in my life but its so much easier to watch someone do it then by reading about it.
Anyways, try it, you'll get better the more you do.
The drill Doctor works & is good for those with no skills, patience or time but you need to keep the little grinding wheel inside up to "snuff" to get the right drill geometry.
GL.....
Rich WA2RQY/4

I learned to sharpen  bits from the "old hands" when I was an apprentice sheet metal worker.....by hand and, by eyeball.    I also learned to make "holedrills" by sharpening a regular bit like the one pictured....They are for drilling nice round holes in thin metal...works very well and you don't get the 8-10 sided type hole from chattering a regular bit thru  thin sheet metal....very handy for radio work..Of course now we have the unibits or step drills which make very round holes in sheet metal

This is a handy tool to have for those of us using the eyeball method of sharpening....It helps you keep the 2 flutes equal length and provides you with the proper  angle.....Especially good for larger sizes

The Drill point guide is a great suggestion for big drills but you will most likely need a loupe for smaller drills.
Correct angle & equal length of flutes might be better for a machine shop but most home users will be lucky to get the drills to cut if done by hand.
The smaller the drill, the finer & better the wheel needs to be(nessessary for thinning web).
For drills 3/16"-1/4", I used a diamond wheel, but again, this was available to me in the shop.
Oh, if you have a real nice coupla wheels on your bench grinder for sharpening, don't let you neighbor sharpen his lawn mower blade on them, the wheels will be useless after that unless you have a nice wheel dresser. I don't mean a star wheel dresser either :o
Put those junky wheels on for rough grinding jobs ;)
7tree.....
Rich WA2RQY/4

You said- REAL men sharpen them by hand, you are correct, so I dont understand why so many came back and suggested such limp things as the drill doctor etc.

I had an old buzzard at work that used to be a tool machinist and he showed me how he lines up and checks the bit after grinding.

He forms a circle with his index finger and thumb. Then puts the tip of the drill behind this circle. This seemed to somehow highlight the features of the drill bit.
I guess its a bit like that artist thing where they from a square with their hands to see what it will look like though the camera.
It seems it provides some focus on the object.
I did ask him but he gave me a short grumpy answer that did mean much.
He learnt it during his apprenticeship.
Does any know this technique and what in particular to look for?

Do 'em by hand...just make them look like a new one...look closely.

First get the cutting edge flat across the stone, then rotate it CW as you swing the shank under and in just a bit.  Do the other side the same, paying attention to keeping it symmetrical.

If you really need to get the angle right, sweat solder two hex nuts together on the flats, it will give you a 120 degrees angle gage.  Just about perfect for bit tips.

73DG

As a Fitter & Turner by trade the first thing we had to learn was drill & tool sharpening, by hand.
There are 2 angles to consider with a drill. The cutting angle should be 118 for steel, 100 for brass and 90 for wood. The second angle is the clearance which should be 12 - 15 deg.
The cutting edges must be the same length or the drill will cut oversize. Reducing the web thickness is only done on large drills and it reduces the force needed to push the drill through the material. It is not required if a pilot hole is drilled first. If the pilot hole is larger than the web thickness the drill will wander.
Large dia. drills are often deliberately made short to stop flexing along their length which causes vibration and results in an oversize hole. The vibration can also cause a high pitched scream.

The correct speed for a drill is 4 x cutting speed / dia.
The CS for Alum. is 250, Brass is 200, Cast iron is 120, Mild steel is 110 feet/min.

I have never worried about the shape of the drill bit tips to match the material.  I use the same drills to cut wood, brass, aluminium and steel and they all seem to work equally well with all the materials without any problem.

I prefer numbered size bits to fractional inch bits, and have a little set that goes from about #50 to #1 or whatever the largest numbered size is, a little smaller than a quarter inch. From that size up, I use fractional inch sizes, 1/4, 3/8, 1/2, etc.

It's nice to be able to measure the size hole I want to drill and find a bit that is exactly that size.  My numbered drills in the set are kept in an "index" holder that indicates the numbered size and decimal fraction diameter in inches for each drill. It also shows which drill to use for each popular screw size (4-40, 6-32, 8-32, 10-24, 10-32, etc) both for tapping threads and for passing straight through, so I don't have to stop look up in a book or chart to determine what size drill to use for a certain screw size.

For wood and sheet metal screws, I measure the diameter of the shank at the smallest part, right in the valley between threads, and drill a pilot hole about 80% the measured diameter.

I can sharpen larger size drills, but don't have much luck with the tiny ones, like #40 and up.

"You need to form an angle of  114° in the drill, you can doit easy with some practice, use a simple grinder, in the sharpen process turn the bit in a shorth half circle for each side. and keep the drill in a 5 to 6°, respect to the axis of the grinder."

It seems a small home made jig could help to help with holding the bit at the correct angles?

Methinks some are too caught up on gadgetry. :P 

To begin with, putting a good edge on anything is a matter of technique, discipline, and practice.  A lot like playing an instument, driving a car, or running a HB rig. 8)

If you have a bunch of defunct bits, practice on them.  What do you have to lose?  All you need is a decent grinder and an acquired knack.  Try them on a piece of scrap and see what prevails.

When and if you come upon the correct style of manipulation, your self confidence will ratchet up a notch! :D

73DG

73DG

Noticed that no one has mentioned web thinning... as you sharpen a drill the web gets wider and the downward force required becomes greater... web thinning allows a machine shop to use a drill bit down to the tang...

http://its.fvtc.edu/machshop1/bench/Webthinning.htm

A belt sander is useful for sharpening drills but to thin a web you would need a grinder...

To check that 114 degree angle, take two hex nuts and hold them together between your thumb and index finger on one of their flat edges. Use the resulting angle on the top or bottom to "gauge" the sharpening progress on your bit.

I already said that several posts back....

73DG

VK7ZL had good comments as were the comments regarding the spur bit for thin metals earlier.
Good (Twist )drill sharpening is best done on specialized machinery . Different point angles, relief angles etc apply very strongly for different uses. While this may not be as apparent for most of the stuff put together by ham radio people proper machine sharpening does indeed make a huge difference in output , tool life and quality over the long haul.The right tool for the job ! The brad point, or tip and spur bit,already mentiond used with a pilot hole provides a fairly good hole in thin metals and wood. These are available store bought but are often shop made from plain twist drills. When drilling grabby metals like brass , the cutting edge of the drill is blunted a bit to avoid the drill hogging and self feeding.( It doesn't take much, A hand whetstone works well on most small drills )
 Most twist drills have flute webs that become thicker as you move away from the tip. This makes effective sharpening of shortened drills increasingly difficult.
  Still, hand grinding and making up of special purpose drills takes place. However for good , productive work within the normal range of sizes we use, machine sharpened drills are hard to beat.
  The right cutting fluids are often overlooked in importance. Most drilling and tapping operations are greatly improved by the application of the correct fluids or compounds.

 BTW: Hole punches are a good alternative to drilling when possible.

How about sharpening hole punches?

I have an old Greenlee 2.75" punch that I've used for 30 years to pop out those common, old buzzard  3" round meter holes.  It's gotten to the point where I needed an extension pipe to make it turn and cut through. Dull, after going thru countless steel and aluminum panels..

I brought it to a metal shop and they waved it off, saying it was difficult to sharpen without ruining it. A friend tried to sharpen it and it appears to be ruined - doesn't cut thru anymore... sigh. I guess once a little metal is removed from one of two halves, the tight fit is gone and it doesn't work well.


This is the one - goes for about $220 now. I paid $40 back in 1972... :-)
http://www.all-spec.com/products/730BB234.html


Anyone have ideas on this?  

T

Tom, you need a good-sized flat wheel to start with.  Take the open end cup part and run it flat against the side of the wheel for enough time to bring up a new surface only.

Then take the punch part and run each shearing edge to the same extent.  Keep the minimal grinding such that the point formed by the two edges is centered.

You will notice that edge is perfectly straight on each side.  If the punch has been ground in any other area, it is probably ruined.

I have many of them and all are still going strong after years of use with this technique.   It also really helps to keep the pull screw lubed with a bit of light oil while using.

73DG

Why pay more ?
This nifty set comes with an ironclad 30 day guarantee:

http://www.harborfreight.com/knockout-punch-kit-91201.html

 :o   ;D

  The male side (punch) and the female side (die) have very little life for sharpening. There is usuall a relief or slight taper to the ID of the die . Some punches have a relief on the OD as well. The set is designed with a clearance between the two, depending upon the material type and thickness. Sharpening should be done only sparingly. If you would like to send the set to me I could probably reweld and grind them to near new spec.

http://amfone.net/Amforum/index.php?topic=26458.0