View Full Version : drill sharpening

plunger

04-06-2011, 05:02 PM

Is there a rule of thumb as to how small a drill is that can be sharpened by hand on a bench grinder. I always thought 6mm was kind of the limit but I sharpened a 4mm drill tonight because I needed to finish a job. It seems that as the drill gets smaller it gets harder to put on clearance.I saw somewhere that a guy made a jig for small drills and used an oil stone instead

Please I come from a civilized country so dont talk to me in fractions or thousands as I just dont understand them :)

.Regards eugene

Walter

04-06-2011, 06:13 PM

I'd offer some insight, but I'm afraid my uncivilized speech would only serve to confuse one such as yourself.

But, let me offer this, so as to ease your suffering when dealing with the less civilized

to convert metric to inch, multiply by .03937

to convert inch to metric multiply by 25.4

cheers

sasquatch

04-06-2011, 06:35 PM

Plunger,, yes somewere there is an article about a guy using a jig and an oil stone to sharpen small drills,,, i have seen it, sorry i cannot remember now were it was. Hopefully someone here will come up with that article.

plunger

04-06-2011, 07:17 PM

Thanks walter I knew the 25.4 conversion but not the .03937 one so it just shows how usefull a sight like this can be. Now do you want to throw a figure at me as to how small a drill is that can be sucsessfully sharpened on a bench grinder. Then I get to use your formula to bring it to a respectible and understandable measurement:)

Thanks walter I knew the 25.4 conversion but not the .03937

Probably because it does not work. I don't where it originally came from but if you use 0.03937 you will end up with an inaccurate figure

metric figure divided by 25.4 = imperial figure

eg 25.4mm divided by 25.4 = 1 inch

12.7 divided by 25.4 = 0.5 inches

-------------------

12.7 X 0.03937 = 0.499999

mechanicalmagic

04-06-2011, 07:27 PM

My rule of thumb:

If I can see it, and hold it, I'll try to sharpen it.

I use a head magnifier, and sharpen down to ~2mm without other aids. Smaller requires a pin vise, and usually I use a single facit. I have sharpened 0.5mm diameter drills by hand. (With a little trial and error.)

DJ

PeteF

04-06-2011, 07:31 PM

I can't answer your first question as I don't sharpen drills freehand, but for the second, this is one site that may help those who were wondering about repointing very small bits. Personally, I use 2 mm a lot and I just thrown them out when they get blunt. A bit wasteful I guess and maybe I should one day look at something like this jig, as the results he's getting look excellent in the photographs. John has a good site and he describes things well.

http://www.gadgetbuilder.com/DrillSharp.html

Pete

lynnl

04-06-2011, 08:02 PM

The .03937 looks suspiciously like the inches per meter value, 39.37, that I learned as a kid. I guess it was a close aproximation. I'd never really checked that out.

Oh well, guess I should've grown up in a civilized country. :rolleyes:

mochinist

04-06-2011, 08:14 PM

Probably because it does not work. I don't where it originally came from but if you use 0.03937 you will end up with an inaccurate figure

metric figure divided by 25.4 = imperial figure

eg 25.4mm divided by 25.4 = 1 inch

12.7 divided by 25.4 = 0.5 inches

-------------------

12.7 X 0.03937 = 0.499999can you measure .000001" ?

where it came from 1mm/25.4=0.0393700787401575

1000mm/25.4=39.37007874015748 "

1000mm*.03937=39.37"

so yeah your figure may be a little inaccurate, but unless you are plotting a course to the moon, you will probably be fine for most hobby sized measurements.

I prefer using 25.4 because it is faster to type.:p

can you measure .000001" ?

That is not the point, the point is 0.03937 is wrong..

mochinist

04-06-2011, 08:30 PM

That is not the point, the point is 0.03937 is wrong..but close enough...if you're uncivilized anyways;)

Dale Lusby

04-06-2011, 08:47 PM

Am I missing something? Using your example 12.7 x .03937=0.4999999999 which is close enough to half inch to not be wrong in my book. All he is referring to is the reciprocal of using 25.4 which is 1/25.4 = .0393700784 to be exact. I can't offer much help as I have a Darex to sharpen my drills which will do 1/16" which unless my my math is wrong is 1.5mm.

NzOldun

04-07-2011, 01:27 AM

Is there a rule of thumb as to how small a drill is that can be sharpened by hand on a bench grinder. I always thought 6mm was kind of the limit but I sharpened a 4mm drill tonight because I needed to finish a job. It seems that as the drill gets smaller it gets harder to put on clearance.I saw somewhere that a guy made a jig for small drills and used an oil stone instead

Please I come from a civilized country so dont talk to me in fractions or thousands as I just dont understand them :)

.Regards eugene

With care (and maybe a magnifying headband) you should be able to get down to 1 mm! Anything smaller, its easier and cheaper to buy them by the (dozen) packet.

NzOldun

Walter

04-07-2011, 05:46 AM

.03937 was the way I was taught when I moved to a shop that ran metric prints regularly. I've avoided the metric system because it's not what I was taught in school.

I look at something and can judge yards, feet, inches and fractions easily. Converting to decimals is almost completely automatic.

I honestly never questioned .03937, but after looking at it i can see the discrepancy. I am not, and never will be a math wiz but the reality is that something doesn't jive.

1/25.4=.03937

.03937x25.4=0.999998

As for small drill bits, I don't personally sharpen anything I can't see well, meaning anything under 1/8 inch gets the Darex. When I worked for the knife company, we used thousands upon thousands of bits 3mm and under, those always got sent out for sharpening. We weren't equipped to do mass fixes like that.

Plunger, and others; without excuses I was in a bad mood and looking to pick a fight. My apologies to all for that. I'll try not to let it happen again.

Allan Waterfall

04-07-2011, 06:19 AM

That is not the point, the point is 0.03937 is wrong..

My Lathe is imperial but I mostly turn to metric dimensions,so When I'm nearly down to finish size I use 0.03937 times the amount oversize to know how far to turn the dial infeed.

eg...

Need 6mm and measure 6.14mm.

Multiply 0.14 by 0.03937 gives....0.0055118"

Divide 0.0055 by 2 and that's the infeed on an imperial dial.

Allan

Black Forest

04-07-2011, 06:30 AM

I recently needed a hydraulic hose. It did not need to be to the mm in exact length. It was not too long as in my hands held apart about shoulder width.

So I go to my friendly hydraulic hose shop and tell him I need a hydraulic hose. He asks how long and what size and what connectors. I tell him the diameter and connectors and then hold my hands up and say "about this long". He shakes his head and tells me to hold my hands up again and then he measures between my hands. While he is measuring he comments about how he can't understand how the Americans could put a man on the moon. Ha Ha Ha.

So for my purposes 0.03937 works fine!

plunger

04-07-2011, 07:08 AM

Hell I am a genuine homeshop hacker .My tape measure is the most used measuring tool in my workshop so all these noughts after the dots is more than accurate for my needs. Walter I am just pulling the piss out of you guys who use such a complicated system. A bit of light hearted fun. I am from africa and some may not think its the most civilized continent to live on. But at least we dont have tornadoes or earthquakes or any natural disasters for that matter.

i never thought about using something like an optic visor to sharpen a drill .I just find that on the small drills it gets hard to get a positive rake clearance. It seems to become a negative rake.

GKman

04-07-2011, 07:27 AM

Black Forest,

Your hose maker sounds like my steel sales clerks. I don't go often but I swear that it is a different guy every time. Anyway they stock in 20' (6 3/32 meters ) lengths and I ask them to cut my order in half so it will fit in my truck. They reach for their tape measure which of course they have laid down somewhere and start looking. I balance the length over my finger or fist to find the center and show them where to cut. They continue to look for the lost tape measure, I guess they don't believe in black magic.

jep24601

04-07-2011, 04:17 PM

Inches to millimeters multiply by 25.4

Millimeters to inches divide by 25.4

Nothing innacurate there.

Tobias-B

04-07-2011, 06:30 PM

That is not the point, the point is 0.03937 is wrong..

...by that logic, everything I've ever measured, cut or drilled is wrong, too...

:D

t

1 centremetre = 0.394 inches. 1 cm = 10 mm. 1 mm = .0394 inches.

mm x .0394 = inches.

Inches divided by .0394 = mm.

25.4 x 1nches = mm.

mm divided by 25.4 = inches.

Don't know which is the more accurate but the results are close, find 25.4 the easiest to use and remember.

Dan Dubeau

04-07-2011, 08:09 PM

My Lathe is imperial but I mostly turn to metric dimensions,so When I'm nearly down to finish size I use 0.03937 times the amount oversize to know how far to turn the dial infeed.

eg...

Need 6mm and measure 6.14mm.

Multiply 0.14 by 0.03937 gives....0.0055118"

Divide 0.0055 by 2 and that's the infeed on an imperial dial.

Allan

With my digital I wind it out to the target dimension in metric, then zero it. Then switch over to imperial, and measure how much is left to come off. Bigger than an inch (only have an 0-1 digital, rest of mic's are inch) then I convert to inches from the start and do it the old fashioned way.

As for drills, like said above, I sharpen them until I can't see them. the smaller ones get replaced. The smallest hole I typically drill on a regular basis is for a 4-40 tap. My sharpening job on a (is it #29 for a 4-40? going off memory) probably not perfect but it works much better than a dull drill.

Paul Alciatore

04-12-2011, 01:47 PM

The two conversion factors, 25.4 mm/inch and 0.03937 inches/mm are reciporcals of each other, but not exactly. 1/25.4 = 0.03937 and 1/0.03937 = 25.4 but not exactly in either case.

The 25.4 is an exact number because the international definition of the inch is EXACTLY 25.4 mm. This is exact. Only the mm or the meter actually is defined in terms of a real world standard. It was not always so, in the past the inch was defined in various ways including body parts and seeds. But at present it is only defined in terms of the meter.

I said not exactly, the more exact conversion is 1/25.4 = 0.03937007874015748031496062992..... I assume it is a repeating decimal but I don't know the length of the repeating string. The error between that and the 0.03937 approximation is about 0.129%. In other words, for a 1 meter length, the error would be about 0.0000787" (about 79 millionths of an incy) or 0.002mm. To put this in perspective, my shop blocks are only about twice this accurate but the longest one is only 4" (about 102mm) which is about 1/10 of a meter. Multiplying up by a factor of 10, says that the conversion is about five times more accurate than my shop blocks. Unless I have greatly misjudged this board, no one here really needs to be concerned about this error. I would bet great sums of money (US or Euros) that no one here personally owns any means of measuring such a small error over such a large distance (1 m).

Point is, use whichever you want and don't worry about it.

As to the original question, I would guess that the smallest that could be hand sharpened with a grinding wheel would depend on the wheel to some extent. A fine grit wheel would be needed. I would guess around 1/32" or perhaps 1/64". That would be about 0.5 mm. But it would probably be hit and miss. Several tries.

Anything under 1/8" or 3mm, I buy the set and when one wears out, I buy a pack of 5 or 10 so I have spares on hand.

I would love to have a set-up that would allow me to put split points on small drills (1mm/1/16" and significantly less) but that is just a dream at present.

Juergenwt

04-12-2011, 04:36 PM

Don't you love the people who make those wonderful prints in metric having dim's like 6.3500127? I used to sent those back asking "high or low side"?

Ron of Va

04-12-2011, 05:21 PM

Back to the question about sharpening small drill bits. I will give a go down to about 1/16 of an inch. I use a magnifying head band, but the real trick (for me) to the small bits is just turning the grinder on, and turning it off when it gets up to about 50-100 rpm’s. Sharpen while the wheel coasts down to an almost stop. Otherwise the bit will disappear into grinding dust before your eyes.

The larger the bit the faster you can spin the grinding wheel without destroying the drill bit.

As far as technique, I have a 59 degree line marked on my grinder support (half of 118º) as a guide.

alchymist

04-12-2011, 07:25 PM

1 centremetre = 0.394 inches. 1 cm = 10 mm. 1 mm = .0394 inches.

mm x .0394 = inches.

Inches divided by .0394 = mm.

25.4 x 1nches = mm.

mm divided by 25.4 = inches.

Don't know which is the more accurate but the results are close, find 25.4 the easiest to use and remember.

If you are really concerned about accuracy - check that little cheap calculator you're using -

Simple test- divide 22 by 7; then multiply the results by 7. If the answer is 22, OK. But I'll bet many calculators out there will give 21.9999 as a result.

So, 0.03937 it is - close enough.

loose nut

04-12-2011, 08:05 PM

Please I come from a civilized country so dont talk to me in fractions or thousands as I just dont understand them :)

.Regards eugene

Maybe those "civilized" countries should have better educational systems so you could understand simple concepts like fractions and "thous".

Jim Hubbell

04-12-2011, 11:21 PM

My HP 15C comes back to 22! 22/7 is a plenty close figure for Pi.

Brett Hurt

04-13-2011, 06:09 AM

The Brooks Cutter Grinder book or blue print Brett

J Tiers

04-13-2011, 08:33 AM

I am a happy bearded barbarian whose preferred clothing is bear skin, but I will tolerate certain other types if they are all I can loot from the civilized people........

As for drill sizes that can be sharpened, I suppose the limit is somewhere in the 0.5mm range as a practical matter, but you would never use a bench grinder for that. I sharpen the small stuff with a fine stone by hand, it only takes a few strokes, but we barbarians are not that fussy.

The biggest problem in sharpening is the grit size.. it needs to be smaller than the object being sharpened so that there is some randomizing of the scratches that are made as the small rocks plow off bits from the drill, which the civilized call sharpening. And so the grit does not knock the top off the item sharpened (as I like to do to noisy civilized folk when sacking a city, it reduces the screaming a lot).

probably 2 or 3 mm is minimum for the average large bench grinder with 150 or 200mm wheel. If you have a dental size grinder, smaller is possible, but you need to be able to hold it , and see the orientation.... we barbarians don't have the patience to fuss, if the drill is dull, we will probably just stick it in your eye and go find a better one.

As for the conversion, whoever said 0.03937 is "wrong" needs remedial math.... as Paul pointed out, the next two figures are zeros, so if you need that much precision, you will have to go and get some dial calipers so you can interpolate between the marks and get that precise....

We barbarians are perfectly happy with 4 place accuracy, anyone who squalls about the next 4 places being important will probably get slit from their guggle to their zatch and thrown out to the wolves.

baldysm

04-13-2011, 11:46 AM

Gotta say that .03937 is correct, but not accurate.

As with anything in the shop, accurate is a relative term. A 5 place decimal is accurate enough for anything any of us will do in a home shop for certain, and also in industry unless you are making something akin to gauge blocks.

I have heard on NPR, that a 30 place decimal is sufficient to measure the diameter of the universe to the nearest atom.

http://www.lowes.com/pd_129477-13261-DDXPK_0__?productId=1010327&Ntt=drill+doctor&pl=1¤tURL=%2Fpl__0__s%3FNtt%3Ddrill%2Bdoctor

My answer for everything less than 1/2".

NzOldun

04-14-2011, 04:06 AM

If you are really concerned about accuracy - check that little cheap calculator you're using -

Simple test- divide 22 by 7; then multiply the results by 7. If the answer is 22, OK. But I'll bet many calculators out there will give 21.9999 as a result.

So, 0.03937 it is - close enough.

Better still feed in 45, then press sin, tan, cos, then arc cos, arc tan, arc sin.

I've seen some of the 'el cheepo' calculators come back more than 5 degrees out. My HP 33s comes back with 44.999631173 (all proper engineers use HP calculators - right? :). Maybe we all need to go back to the slide rule (I know I have my old one laying around somewhere!!

NzOldun

J Tiers

04-14-2011, 08:50 AM

Better still feed in 45, then press sin, tan, cos, then arc cos, arc tan, arc sin.

I've seen some of the 'el cheepo' calculators come back more than 5 degrees out. My HP 33s comes back with 44.999631173 (all proper engineers use HP calculators - right? :). Maybe we all need to go back to the slide rule (I know I have my old one laying around somewhere!!

NzOldun

A Ti-30Xa comes back with 44.99963117..........

"proper" engineering calculators?

I would tend to agree that HP , and specifically the 41, 41CV, are indeed the only acceptable engineering calculators...... I have one.....

But, since the unreliable SOB quit working after only 25 years, and one cannot buy them (or anything like them, and in fact, HP no longer even exists), I have started using the TI-30 type, which are demonstrably inferior (I know that MUST be somehow provable), but can sometimes provide the right answer.

They produce answers close enough for a barbarian, but are somehow lacking in the shiny bling we barbarians love.

I have noticed a difference between calculators and drills.... When you rub a calculator on a rock, it does not get sharper. This is puzzling..... I need to go burn the toes of some civilized citizen until he tells me why that is.

dalee100

04-14-2011, 11:05 AM

Hi,

My $1 no name Dollar Store calculator comes back with 44.99963117.

/forever a crude Barbarian

dalee

plunger

04-14-2011, 12:59 PM

I wasnt trying to offend you barbarians .But this is my point apart from trying to figure out how small a drill one can sharpen. Being from a civilized country(s africa) and not having to deal with your crappy measuring system means I can do all my calculations on my fingers without even having to own a calculator. What is even more convenient is I can do halves as well ( The only real advantage of having chopped my finger off)

Thanks for all the advice guys

Regards Eugene

J Tiers

04-14-2011, 11:20 PM

I wasnt trying to offend you barbarians .But this is my point apart from trying to figure out how small a drill one can sharpen. Being from a civilized country(s africa) and not having to deal with your crappy measuring system means I can do all my calculations on my fingers without even having to own a calculator.

Ah, I misunderstood..... it is mm you do not like......... that is what I use.......... And I thought you were talking about a different system.....

No matter, barbarians grab "enough", we don't need to measure. "Enough" is about as much as we can carry, if it looks valuable.............

Forrest Addy

04-15-2011, 12:34 AM

Personally I use the atto-parsec as a length standard. That's about 2.4308 muscular inches or 61.74 pansy millimeters. Atto-parsecs make about as much sense as any other standard in the absense of platimum-irridium barley kernels from the middle of the ear.

Black Forest

04-15-2011, 01:10 AM

You all are on drugs and alcohol in a big way!!!

darryl

04-15-2011, 02:01 AM

Once you get down to roughly .3429 mm, it becomes a bit difficult to sharpen drill bits.

Now shame on you all for reaching for the calculator- everybody in the civilized world knows that's a #80. Now go have a drink- I am. Southern Comfort, mm :)

loose nut

04-15-2011, 11:39 AM

I wasnt trying to offend you barbarians .But this is my point apart from trying to figure out how small a drill one can sharpen. Being from a civilized country(s africa) and not having to deal with your crappy measuring system means I can do all my calculations on my fingers without even having to own a calculator. What is even more convenient is I can do halves as well ( The only real advantage of having chopped my finger off)

Thanks for all the advice guys

Regards Eugene

People who use the metric system can't help but offend us barbarians.

shifasaw

04-17-2011, 09:27 PM

hi friends i have build tyer bandsaw machine i would like to know what is the air fill inside the tyer and my machine main axcel getting broken why ? and i have used toyota hiace van axcel after reduse diameter its get broken please give me solution for this thanks

Mayhem

04-20-2011, 10:17 AM

Better still feed in 45, then press sin, tan, cos, then arc cos, arc tan, arc sin.

I've seen some of the 'el cheepo' calculators come back more than 5 degrees out. My HP 33s comes back with 44.999631173 (all proper engineers use HP calculators - right? :). Maybe we all need to go back to the slide rule (I know I have my old one laying around somewhere!!

NzOldun

Tried this on the calculator that comes with Windows and it returned 45 each time.

dvbydt

04-20-2011, 12:29 PM

Before the days of CNC grinding, I asked a dormer rep. how they sharpened small drills. He said young eyes, a magnifier, fine grit aluminium oxide wheel and a stroboscope to make the wheel stop. Try it if you have one, it's magic!

I've been metricatred for years, I am happy with the system and won't budge an inch from that view.

Ian

Black_Moons

04-20-2011, 04:30 PM

Tried this on the calculator that comes with Windows and it returned 45 each time.

Wheres the arc X buttons? Are they the CosH etc buttons? if so I don't seem to be using them right..

MarcAG

04-20-2011, 09:40 PM

Yes, that's right, get any one of "'three classic HP calculators: the HP 12c, HP 12c Platinum, and HP 15C" for your iPhone.

Can't stop ?progress? can we.

Yep, I live in metric Canada, schooled metric. I work in metric, my clients work mostly in ft-in, and my home shop stuff (wood and metal working) is imperial.

I can't seem to find any 8ft X 50.8mm X 101.6mm lumber!

Oh ya!!.. that's cause they aint actually really 2"X4"...

I'm confused...