Can drill bits be re-sharpened?

[fast ronnie]

Done it for many years, but I worked in one shop that didn't allow sharpening as the boss said it took too long. I quit there after a year because of some shenanigans they pulled with me. Penny wise, dollar foolish.

[smokeywolf]

During my apprenticeship I ran the toolroom. I've sharpened thousands of drills. Used to be able to split the point on a 3/32".

Some folks catch on to drill sharpening and some don't. If you go through a lot of drills a Darex or a "Drill Doctor" might be a good investment. Someone suggested internet videos; a very good idea.

Only brands I'll spend money on are Cleveland, Union, Chicago Latrobe, Precision Twist Drill, Guhring and a couple of others. Nitrided (TiN or TiAN) drills are nice, but unless you're machining stainless or titanium they may not be cost effective.

[Bulldogger]

I lucked into a good deal on a Drill Dr years ago at e liquidation sale. Have had good results with it, except when I pushed the bit too hard when drilling and lost the temper. I'm getting better at doing it right. I am not in the workshop enough!
BDGR

[oldred]

side webs would wear on them also making it a taper drill if you didn't take enough off.

That's an often overlooked point that has left many folks wondering why their freshly sharpened drills will seem to start out Ok but then stop and refuse to drill. I have seen it many times, a sharp lip with the proper angle and reliefs but with the side flutes chipped/worn which makes the point a smaller diameter than the rest of the drill. That problem is often seen with Drill Dr type tools since they tend to do more of a touch up type sharpening rather than removing a lot of material, this leaves a nice sharp new looking tip but if those flutes are worn back or chipped then no matter how sharp the tip the thing is not going to drill. The main part of the drill simply can not fit into the material if the tip is drilling a smaller diameter hole than the rest of the drill! Sometimes the drill needs to be ground back quite a ways to get full flute diameter even though the tip itself may look perfect after just a light touch, in fact some abused drills should just be tossed if an inspection reveals chipped, gouged or excessive side wear.

[EMC45]

Watch you angles and heat (temper) and a grinder will do.

[Willbird]

Hand sharpening drills is indeed a worthwhile skill to learn. Also how to make a flat bottom drill by hand grinding for when you want or need one. Bigger stuff, say much over half inch if there is a belt sander handy it will do a nice job with same technique.

If you grab a 0-1 micrometer and measure a drill to the .001, then hand grind it you can judge how well you centered it by measuring the drilled hole dia. The best drill grinders I have ever used look like this..



One can take a drill that measures .375, sharpen it using that style drill grinder, and usually the drill hole will not accept a .377 gage pin, maybe not even accept a .376. There are a million other drill grinders but where they fail is having an adj for centering that always seems to be just a touch off, a drill tip .002 off center will drill a hole .004 bigger than the drill.

One shop I worked in had drills that some of them started out literally 18" long, and had been sharpened and shortened down to 6". Well a drill is tapered on the OD, a 18" long drill of a decent dia (say 1") might have .005 taper. The web also gets much thicker the further back you go. So those shortened drills sucked. The crib guy would try to grind them intentionally off center so as to make a 1" hole...they would until the drill tip broke through, then the last 1/8" or more of the hole would end up drill dia, or undersize .

Bill

[country gent]

On some of the drills from the plastics plant we set up a cut off wheel in the surface grinder and took 1/4" - 1/2" of then started over. That was quicker than grinding form back that far. The fiber glasses and some plastics were really abrasive on those drills.

One other overlooked benefit of sharpened drills is the shorter drills are stiffer for a given size and don't wander as much. I have an 18" 5/16" full flute bit that's like a spaghetti noodle in a drill chuck, a 5/16 jobbers length 3" length is much stiffer and a hand ground 5/16 spot drill 1 1/2"length is very stiff

[bob208]

if you can use short drills get screw machine drills. the are 1/3 shorter then the common jobber length.

[Traffer]

Done it for many years, but I worked in one shop that didn't allow sharpening as the boss said it took too long. I quit there after a year because of some shenanigans they pulled with me. Penny wise, dollar foolish.

Any shop where the boss won't let you do basic maintenance like sharpening drill bits is not a decent place to work. That guy will end up with bitter workers. Eventually some of those bitter workers will sabotage his shop. Then he will really have some extra expenses to deal with.

[country gent]

Costs to much to sharpen drills ????? We had 2 cutter grinders per shift and 2 cnc cutter grinders in the tool room to maintain production tooling. drills, reamers, and other cutters were sharpened in house. lot of the new tooling came thru the tool room first for a "touch up" before going to production. These guys were very good. Also had 3 manual cutter grinders ( Norton if memory serves). about the only thing not sharpened was the carbide inserts.
In the tool room we had twist drills to 3" dia and spade drills to 6" these bigger drills were $400.00-$500.00 when new to not sharpen was foolish. On bigger drills we not only sharpened the drills but replaced worn morse tapers and tangs. The spade drills were great when sharp and would really make a chip.

[smokeywolf]

Back in the '90s I had a connection who worked for a defense contractor. Many of their end mills were not permitted to be re-sharpened. When I ran the Studio Machine Shop at Sony/Columbia, my friend would stop by once or twice a year with a box of dull end mills. Didn't have a dedicated cutter grinder in the shop, so I'd send them out to be sharpened at $7.00 to $17.00 ea. Would end up with $800 worth of end mills for about $200.

[bstone5]

Purchased a Darex many years ago and have sharpened thousands of drill. The Darex model I have has been discontinued and therefore purchased some spare parts when Darex notified me the mode was being discontinued.
Still will sharpen by hand when in a hurry.

[Traffer]

Basically anything that has been sharpened can be sharpened. The more you sharpen stuff the better you get (like anything else). The difficulty comes in keeping things symmetrical ... all blades on the same cutting plane. It's relatively simple with a twist drill with two flutes and therefore two cutting blades. It starts getting difficult when you have multiple cutting surfaces like most hand or chucking reamers. Those are nearly impossible to sharpen without machinery. Curved blades also present a challenge. Things like router bits with ogive curves etc. I have been practicing grinding bits to make bullet ogive points. I use them for cutting point forming dies and bullet molds. I use twist drill bits for that purpose. I have also learned to sharpen end mills and make crude end mills and specialty bits from twist drills. I don't use end mills on milling machines. I just use them to make blind holes with square bottoms. It's all about practice. When you can get drill bits and end mills very cheap, why not use them to practice sharpening skills. Especially if you purchase dull or broken ones. There is very little to lose and much to be gained. The same principle applies to the dremel type grinding wheels. Since the diamond coated wheels only cost pennies. The combination of grinding a 50 cent drill bit with a 20 cent diamond wheel is a no brainer. That is if you have the time and desire to learn. I have posted several videos of grinding specialty bits with dremel tools but no one seems to be interested so I deleted most of them. If I were to advise someone about sharpening drill bits or anything else for that matter, I would tell them to "Study the angles" that you have to duplicate. Once you learn basic grinding skills it is all about the angles. People limit themselves way too much. When you have in your mind that something takes a genius or rocket scientist with expensive tools you are hurting yourself. I would rather fail miserably trying to do something out of my league than stay away from doing things because they seem difficult.

[Drm50]

Anything much smaller than 1/8" is hard for me to see. I've sharpened them on a grinder since my
old man taught me as a kid. I got a Dr Doctor for Christmas but haven't used it yet. Some drill bits
are not worth sharpening, made in China.

[stu1ritter]

I'm a retired Mercedes-Benz mechanic and I always sharpened drill bits by hand. Was taught how many years ago. A friend gave me a drill doctor as a present, I tried a few bits and realized the hand is never quite as accurate as the machine, close, but not quite. I spent a day going through all my drill bits with the Drill Doc and was quite satisfied with the results. Nice little machine and it does take a light touch.

Stu

[Willbird]

Basically anything that has been sharpened can be sharpened. The more you sharpen stuff the better you get (like anything else). The difficulty comes in keeping things symmetrical ... all blades on the same cutting plane. It's relatively simple with a twist drill with two flutes and therefore two cutting blades. It starts getting difficult when you have multiple cutting surfaces like most hand or chucking reamers. Those are nearly impossible to sharpen without machinery. Curved blades also present a challenge. Things like router bits with ogive curves etc. I have been practicing grinding bits to make bullet ogive points. I use them for cutting point forming dies and bullet molds. I use twist drill bits for that purpose. I have also learned to sharpen end mills and make crude end mills and specialty bits from twist drills. I don't use end mills on milling machines. I just use them to make blind holes with square bottoms. It's all about practice. When you can get drill bits and end mills very cheap, why not use them to practice sharpening skills. Especially if you purchase dull or broken ones. There is very little to lose and much to be gained. The same principle applies to the dremel type grinding wheels. Since the diamond coated wheels only cost pennies. The combination of grinding a 50 cent drill bit with a 20 cent diamond wheel is a no brainer. That is if you have the time and desire to learn. I have posted several videos of grinding specialty bits with dremel tools but no one seems to be interested so I deleted most of them. If I were to advise someone about sharpening drill bits or anything else for that matter, I would tell them to "Study the angles" that you have to duplicate. Once you learn basic grinding skills it is all about the angles. People limit themselves way too much. When you have in your mind that something takes a genius or rocket scientist with expensive tools you are hurting yourself. I would rather fail miserably trying to do something out of my league than stay away from doing things because they seem difficult.

My very first full time job out of Vocational High School was in a tool and cutter grinding shop. If I would have PAID every day to be there it would still have been worth it . Some basic stuff I picked up way back in 1981.

On HSS tooling, for the most part a 7 degree primary and a 15 degree secondary relief angle will work for almost anything.
For carbide tooling a 5 degree primary and a 10 degree secondary will work for almost anything.
You can spin grind or OD grind a form onto a tool, might be a radius or a taper...then blacken the OD with a sharpie marker and back it off until only a "hair land" remains of the original OD grind. This technically is called a margin...and the margin width you need will vary with the tool, a straight flute reamer for example will have a bigger margin, a morse taper reamer may only have a hair land...if it is too narrow it will dig in and grab, if it is too wide it will not cut.

You may ask "how do I verify that I am getting a 7 degree primary relief angle" ?? Well 1 degree of fall in 1" is .016"...pretty much. So we would grind a 1/16" wide primary, then measure the fall in 1/16" with a dial indicator as we rotate the cutter (for an od relief)...and if we see .007" fall in 1/16" we are very close to 7 degrees.

TECHNICALLY the degrees of primary relief on a cutter is varied (more degrees relief on a smaller cutter) with diameter BUT 7 primary and 15 secondary actually works quite well.

If you are re grinding an endmill you want to end up with what they called a "walking cutter"....the cutting tips will be taller and the center will be lower. If you take a steel plate, and a sheet of paper, and lay the paper on the plate, then press the end of an endmill down, and rotate backwards a bit, you will see how the cutter is relieved...it is easy with the flute shape to think you have some dish but in reality the center is higher, that will leave a really bad finish .

Hand grinding cutters if nothing else is a way to easily remove a lot of material, if the end of the tool was badly damaged, if you know how to grind a drill you can snag it off by hand to get rid of the ruined metal, then put it in the drill grinder. Most drill grinders if you remove much stock you have to re position the cutter due to the helix of the flutes.

Chucking and other reamers often have the flutes spaced in an intentionally irregular fashion to help alleviate chatter...so if you re sharpen them even in a machine you need to reference from the flutes, trying to use say an even 6 index on a 6 flute tool will not work.

The really killer way to grind a tool is called "form relief"....the cutting edge is not a primary, and secondary, and maybe a third relief, it is all one smooth intentional curve...but it is really difficult to to to begin with, and even more difficult to re sharpen...but a twist drill actually DOES have a form relieved end grind, it was worthwhile enough to devote the time to develop ways to generate and duplicate it . Another example of a form relief is the single flute chamfering tools.

If your drill grinder was broken, or you have a huge drill, you CAN put the 7 degree primary and 15 degree secondary on the end of it, then hand grind the rest of the relief and it will work really nice .

One more tip to check the reliefs on the end of a tool, if you were grinding say a 45 degree chamfer tool, or even a form tool for a swaging die, if you find a hole in something to sit the tool into, you can make sure you actually have an OD relief and nothing is touching, it is pretty easy to think you have enough relief but something is actually dragging way back behind your primary and secondary.

Bill

[smokeywolf]

A lot of very good information there Bill. Thanks for that very nice write-up. Most of us old timers who spent half our lives in machine shops know this stuff, but a lot of home/hobby machinists don't.

[Willbird]

A lot of very good information there Bill. Thanks for that very nice write-up. Most of us old timers who spent half our lives in machine shops know this stuff, but a lot of home/hobby machinists don't.

yes most of us can look at a tool and say "that will not work" . I grabbed a router bit one day at work and said "nope that will not work"...co worker says "why" ?? I said "because it has no OD relief"...it had about 1/16" of round OD ground margin on a 1/2" cutter. The tool is used to cut out the window opening in a steel skin entry door. he says "I think it looks OK".....so I said "OK go ahead and give it a shot" . As you or would both know looking at the tool it did not work .

[smokeywolf]

yes most of us can look at a tool and say "that will not work" . I grabbed a router bit one day at work and said "nope that will not work"...co worker says "why" ?? I said "because it has no OD relief"...it had about 1/16" of round OD ground margin on a 1/2" cutter. The tool is used to cut out the window opening in a steel skin entry door. he says "I think it looks OK".....so I said "OK go ahead and give it a shot" . As you or would both know looking at the tool it did not work .

Have to have sufficient relief so that as the cutter is advanced it doesn't heel.

[wrench man]

The drill bits I sharpen on a bench grinder usually don't cut much better than before I sharpen them??, I have a Drill Doctor with both chucks for up to 3/4", bits sharpened on it will make two curly Q's until they pop out the other side of the material!

I can sharpen lathe bits, Carbide or HSS on the bench grinder and make 20' long curly Q's on steel, cast iron makes nice chips and is smooth as a baby's but!