Sharpen blunt drill bits or just buy new ones?

[Afterimage]

Drill bits are getting cheaper all the time and when they get blunt I just buy new ones,but now I have a pile of blunt drill bits in a box that I'd like to recycle.
Is a re-sharpened drill bit as good as a new one?
What's the best way to sharpen a drill bit?

 

[Archie]

I think the results you get when sharpening drills depend on the quality of the drill in the first place. I've been told the cheaper ones only tend to have their tips hardened so sharpening a couple of times quite often removes the hardened area. The more expensive ones should sharpen many times.

With a bit of practice you can get good results on a bench grinder. Making sure the flat bit at the very tip remains central is the bit I always struggle with though I've not done it much. Otherwise I don't think that drill sharpeners are very expensive.

 

[Wozzaaah]

I've been told the cheaper ones only tend to have their tips hardened so sharpening a couple of times quite often removes the hardened area. The more expensive ones should sharpen many times.

You're right there archie, I once tried sharpening a snapped cheapo bit, it was useless.
I've always done them on a grinder too but with mixed results, small ones are very difficult to grind accurately but then they're peanuts to replace.

 

[Hitch]

Anything above about 4mm i resharpen.
If you buy good quality ones, they last for ages without the need for sharpening.
And when they do, i always do them freehand on a bench grinder.
That way you can grind them how you want them to suit different jobs.

 

[Archie]

That way you can grind them how you want them to suit different jobs.

Interesting. I assume you change the pitch? If so, what suits what, if you get me drift.

 

[Hitch]

Flatten the point out a bit for drilling thinner stuff.
sharper point for pistol drilling without centre punch marks...
Im sure if you ask someone that does a lot of machining, theyll explaint it.
Sometimes taking some meat of the back of the bit reduces heat, usefull for stainless.

Comes with practice, a few degress either way doesnt matter much imo.

 

[snowcat]

The point angle is different depending on the material to be drilled, theres LOADS, but most importantly are 118 degree for standard LCMS an 135 for S/S, the relief angle is dependent on the size of the drill, and the harder the material, the more relief (or the less) angle is put on, short answer is to reduce drag...

On the subject of sharpening yes I do, personally I consider cheep bits only fit for the scrap bin, this was reinforced to me once when I had one explode in the tail stock, cutting my head fingers, and missing my eye by a nats cock.......

Off hand grinders can be used to give a reasonable re-sharpen with practice, dressing wheals helps, but remember to sound!!, although larger bits 3/4">, I run to a local toolmakers after a sharpen or two for a proper regrind, It surprising how far oversize they start to drill over wise, although drilling is only ever a roughing procedure, but plenty accurate I'm sure for most forum members....

 

[Drains]

Mickj, the best way to deal with blunted or broken drill bits of any size, is to send them to me!

Sharpening bits isn't difficult, at all, even down to a mill (or two) with a fine stone and a fine touch (and a magnifying glass). They get difficult when short, as the web between the flutes gets thicker towards the shank of the bit, but there are simple techniques for dealing with that, which I can't describe in words. Maybe I could do some pics if you're interested.

Must say, I never throw away a bit that's not bent. No need at all. And if you buy bits that are any good in the first place they'll cost too much to throw away. Buy quality. Don't be a part of the throw-away, consumerist society.

 

[Archie]

although drilling is only ever a roughing procedure, but plenty accurate I'm sure for most forum members....

If there's one available, I always use the mill instead. A 12mm drill will never drill a hole 12mm round. Either that or I've been known to drill a decent sized pilot and drill with the counterbore!

 

[snowcat]

Although archie a properly ground 1/2" bit should only run 0.003" oversize IF its of decent quality and sharpend true...... Of course a reamed and bored holes should be 100%...

 

[Archie]

You've hit the nail on the head there. "Properly ground"! I remember making 16 nylon bushes at school for a project a friend and I were doing in our spare time. Drilling them on the lathe resulted in about a 0.5mm discrepancy and there were only hand reamers available. Decided they were absolute crap so I used the counterbore instead. Only thing was the counterbore only came in a couple of sizes so I had to make adjustments to the rest of the design so that I could drill everything that needed to be accurate with it! Worked out in the end, though!

Interesting about the different angles. I think I'll just stick to getting it even!!

 

[gavuk]

still use two nuts welded flat to flat, point drill towards weld,....angle between nuts is 120 degrees close enough for me,saves making darts...........

 

[Archie]

still use two nuts welded flat to flat, point drill towards weld,....angle between nuts is 120 degrees close enough for me,saves making darts...........

Cunning. I'll have to give it a go.

 

[snowcat]

You've hit the nail on the head there. "Properly ground"!

jeuss 0.5mm whats that around 0.020", I have a fealing the tailstock could have been a wee touch out to be that far out......

 

[Archie]

jeuss 0.5mm whats that around 0.020", I have a fealing the tailstock could have been a wee touch out to be that far out......

It wouldn't surprise me. I always treated that lathe really well (spent hours on it) but not everyone did. Still the counterbore gave us a fit of about 0.01 mm which was plenty good enough!

Saw your cutting on the dividing head earlier. Awesome idea. My mate and I made 16 bevel gears on the mill with one of those. NEVER again. Took us the best part of a term!!!

 

[gavuk]

used hand reamers in lathes before ,just very slow ,also thin cutting oil gives tighter hole than thick cutting paste........boreing bar for real accurate (bearing fit)every time ,in my experience

 

[Afterimage]

Sharpening bits isn't difficult, at all, even down to a mill (or two) with a fine stone and a fine touch (and a magnifying glass). They get difficult when short, as the web between the flutes gets thicker towards the shank of the bit, but there are simple techniques for dealing with that, which I can't describe in words. Maybe I could do some pics if you're interested.

If you could give me a brief tutorial on drill bit sharpening I'd be very grateful,I'm all for recycling and saving the planet - especially if it helps to save some money too!

 

[Luke]

I have found this post useful for learning how to sharpen drill bits.

I'd like to learn more though

 

[Wozzaaah]

A couple of things I've found when resharpening bits is that it's quite easy to get the cutting edges uneven so the point is off-centre making it drill oversize holes. Also it's obviously important to make sure that the face slopes down away from the cutting edge fully, it's very easy to sharpen a bit and actually grind a slight slope towards the edge therefore rendering it pretty useless.
I like Gav's idea of the two nuts as an angle guide .

 

[gavuk]

a few years ago a co i worked for had a drill powered sharpener,,,worked ok ,but was time consuming due to drill being primary power source,small stones used,and drills being held in collets,so it was fiddly,,,,,has anyone tried the attachments (draper style)that attach to toolrest on bench grinder?often wondered if they where easy/fast to use ,angles would be ok these are set using protractor scale,what about clearace and rake,used something similar for slotdrill/end mills which worked well ,how about drill attachments?????