Off hand grinding drill bits

That isn't Tubal Cain!

Tubal Cain (Tom D. Walshaw) died in 1998. The YouTube chap is shamelessly passing himself off :-|

Mark Rand RTFM

te:

But then again Tom walshaw wasn't Tubal Cain either, he was also passing himself off.

Goes every new generation need a Tubal Cain ?

John S.

Never used a jig, so I can't comment on that. But his technique looks good. It's not quite what I do, but it looks like it should work well.

Yes, I'd think so. But ... I think his explanation sucks a bit, here:

Yep.

I think that maybe the initial tilt you mentioned above *is* the 10-12 degrees he's talking about - the rotating action just grinds the rest of the end well out of the way. It takes quite a bit of grinding to get rid of all the unwanted material. The rotating action will not produce a flat surface with a consistent angle anyhow.

Or at least that's how I do it.

Worth a try, indeed. Big drill bits are expensive and are not hard to sharpen by hand. I also entirely agree with his "throw the small ones away once they are blunt".

One caveat, to watch when you first start grinding - the wheel or belt can grab the bit and hurl it around if you don't hold it firmly enough. On the other hand, you don't want a death grip either, if it's sticking you want to be holding it loosely enough that the movement in your hand frees it - firm but loose, it takes a little bit of practice to get the feel of it, but that's all.

I also use the lip of the grinder as a steady, while he's doing it almost in mid-air. He's better at it than I am though!

Maybe wear leather gloves and apron (plus the always eye protection), at least when first starting out? Nah, perhaps not gloves, just a full face shield.

-- Peter Fairbrother

Ah, right-o.

After a bit more head-scratching plus looking with an eye glass at a brand new drill pressed to a flat plate, I think I'm beginning to see what this is seeking to achieve. The drill cuts in a (very) shallow helix as it advances into the work, so if you didn't grind "the rest of the end well out of the way" it would rub against the bottom of the hole. A new drill seems to come with this part of the face not flat either.

Nah, gloves just defeat any sense of feel, but eye protection makes sense.

Alan

Some new large drills, and some cheaper new smaller drills, are ground with only two flats, but quite a few new drills are ground on four surfaces.

The first two surfaces are much the same, the second two are flat and do two things at once - first of all they get rid of the excess at the back edge of the triangle, lessening the depth of the cutting edge, and second the flats are continued so they each remove a quarter of the chisel point.

This results in a single point, not a chisel, at the very center of the drill bit, and the chisel also gets some cutting edges.

This means that it will cut directly into materials without a pilot hole, much easier and better than the older two-p. It may be the reason behind the new-ish US-ish enthusiasm for not step drilling larger holes, but just drilling them all at once.

I think this is called split point sharpening. If you have a drill sharpened this way it should be easy enough to understand this, if not it may well be beyond my ability to describe!!

I can't grind split points, certainly not by hand, so for larger bits I use the old method of two flats plus a rotate to get rid of the excess (shortening the depth of the cutting edge, thereby reducing drag), and use a small drill first. I don't worry about the chisel point, as I'm not going to use it.

There is also the bullet point sharpening method, which is another one which is best left to the manufacturers, but for small drills it stops the drill wandering - not quite as good as a center or spotting drill, but not bad, and they are cheap and disposable.

-- Peter Fairbrother

"Tubal Cain" is probably getting usable drill points from his procedure but not if the procedure is followed as he describes it..

All the cutting action of a drill point is within a few thou back from the cutting edge. The rest of the metal is shaped to provide mechanical support to that edge and to avoid fouling the freshly cut surface (clearance).

Considering the cutting edge alone - this cuts a spiral into the workpiece as it feeds into the work. This limits the acceptable feed rate. If the feed rate is ever high enough for angle of this spiral to reach the cutting edge angle the cutting clearance drops to zero and the drill cannot cut properly - only push metal out of the way.

For the same feed per rev, larger drills generate a smaller spiral angle and can tolerate a smaller (stronger) cutting angle typically 10 deg. Smaller drills need steeper angles. One manufacturer recommends:-

over 18mm 6 to 12 deg

10 - 18 8 to 12 deg 6 - 10 10 to 14 deg 1-6 12 to 18 deg

I actually tried it yesterday and wasn't impressed. for a start the bump / join in the belt causes it to move and create a flat you don't want, usually on the cutting edge and it drags the drill down so you get a negative angle.

After a couple of goes I got a passable grind which cut.

Ironically I can do better with one of those jigs he was hitting with a hammer,

I do grind drill bits on the belt sander but with the cutting edge vertical and then push and twist. For anyone wanting to try this it may pay to make a Vee grooved 'launching ramp' shape in wood to support the drill.

John S.

PS. If he's the original Tubal Cain does this mean God is American ?

Probably as they claim the first for everything. Only thing they do have a first for is loosing wars, they have never won one yet, even the Italians have won more. They even lost their own civil war

In article , Peter Fairbrother writes

Peter,

I think you may be talking about two quite different methods, four facet and split point. The former has the 4 facets meeting at a pyramidal point, and as the facets are planes the shape can be ground on the face of a wheel with simple holders. The split point has two undercuts which need to be cut with a sharp corner of a wheel.

The four facet has one of the disadvantages of the conventional shape, in that the centre does not cut, it blasts its way in through plastic deformation, but it does have two advantages: it is self-centring, and it is perhaps the easiest shape to produce on a T&C grinder or a bench grinder with a simple sliding angle rest. No special jigs are required. The split point style does actually cut in the centre, but is harder to produce; it probably comes into its own above 10mm or so (at which size it gets easier to produce).

David

I actually tried it yesterday and wasn't impressed. for a start the bump / join in the belt causes it to move and create a flat you don't want, usually on the cutting edge and it drags the drill down so you get a negative angle.

After a couple of goes I got a passable grind which cut.

Ironically I can do better with one of those jigs he was hitting with a hammer,

I do grind drill bits on the belt sander but with the cutting edge vertical and then push and twist. For anyone wanting to try this it may pay to make a Vee grooved 'launching ramp' shape in wood to support the drill.

John S.

PS. If he's the original Tubal Cain does this mean God is American ?

Probably as they claim the first for everything. Only thing they do have a first for is loosing wars, they have never won one yet, even the Italians have won more. They even lost their own civil war

Genesis 4:22 says that Tubal-cain was the "forger of all instruments of bronze and iron" (ESV) or an "instructer of every artificer in brass and iron" (KJV).

So he must be a really old bugger...doesn't mention a belt sander though.

On Thu, 28 Oct 2010 14:37:09 +0100, snipped-for-privacy@yahoo.com wrote: snip

I must admit to the "grind two cutting edges, then grind some clearance" method. Works for me.

His comments on the grinding jig are rubbish. Set up CORRECTLY this type of jig can produce a good balanced cutting edge on drills large and small. My tips would be

1 Set the jig up to grind towards the top of the wheel at near 12 o'clock. This ensures that the grinding action is at 90 degrees to the cutting edge. 2 Dump the bit of tin that supposedly touches the helix edge of the drill. Whilst this allows you to create a definite 180 degrees between cutting edges, the cutting edge can only be "vertical" at zero clearance from the wheel. As the drill overhang is increased the cut edge alignment changes because the bit of tin touches further down the helix. 3 So position the drill so that the cutting edge is vertical by eye. 4 Adjust the overhang in line with the jig instructions but be ready to adjust to generate the correct chisel edge angle and therefore clearance. 5 Take small cuts.

If anyone has one of these jigs and has had problems in the past, the above may help (or not!). In my mind the jig is best used when one has a number of drills (of the same or similar size) that need sharpening.

My jig now about 45 years old (cannot remember what I paid for it) is not used often but has been useful over the years.

Richard

What I have found the jig useful for is getting back into the swing of freehand grinding, Often after a long spell of not grinding any drills the first few come out crap, grab the jig, do a couple and you seem to get the hand, eye and wrist movements back again.

One thing i have noticed with the modern jigs is the base is recessed and it looks as if it was designed to sit on the inner recess which is a different angle from the base.

I linished mine flat and followed the recessed shape and it sees to work OK.

John S.

I much prefer to use the side of a cup or straight wheel for light drill point grinding. It's so much easier to eyeball the correct angle than when trying to use the periphery of a straight wheel.

Strictly speaking I should always use a cup wheel but it's much easier to use the wheel that's already mounted and that's usually the straight wheel. This sounds a bit cavalier and I'm sure that there will be lots of dire warnings but there is at least some method in my madness.

I use straight vitrified bond aluminium oxide wheels typically A60KV. The internal structure of an A60KV cup or straight wheel is identical. As initially manufactured the vitrified bond material covers much of the abrasive grains on both the sides and periphery of the wheel.. This surface is unsuitable for grinding so straight wheels are supplied with the periphery dressed true, cup wheels with the face dressed true.

If the side of a straight wheel dressed in this manners it is every bit as strong and good as a cup wheel. The only important difference is the support given to the other side of the wheel by the grinder flange. Mounting instructions for cup wheels specify that the flange should be large enough to provide support at least up to the inner radius of the cup i.e the inner radius of the grinding area. If straight wheels are mounted, dressed and used in this manner there is no essential difference in the resulting stresses in the wheel.

Health and Safety enthusiasts will no doubt point out that generic manufacturers instructions forbid side grinding on straight wheels. This I accept. This note simply decribes methods I have used for many years without problem.

Jim.

When I said

I was naively thinking the moniker on the vid was unique and specific to the deceased UK author. It seems there are charlatans everywhere. As penance I've looked up "Drills, Taps and Dies" in the Workshop Practice Series by the "real" Tubal Cain. He thought those Potts-type jigs are good, to the extent that he deprecated off-hand drill sharpening for any sort of precision work.

He mentioned, in passing, the need to twist the drill with a wrist action as well as swinging it vertically if you intend to reproduce off-hand the "correct" offset conical tip, rather than a simple cylinder. John-S also hinted that he does this, but he seems to be in a minority (along with Richard Shute). I thought my jig was taking this simpler approach until I saw this

which points out that the swing axis is inclined towards the grind wheel. I suspect this may be mimicking the wrist twisting of the skilled off-hand grinder, but it will need someone who is a lot more of a clever clogs than I at Euclidian geometry to work that one out.

One last point. Richard Edwards said

and that's what Gadgetbuilder says too. My jig, which is a "Fig 9" made by Picador looks the same but the idiot sheet says to set the cutting edges to "five minutes to five o'clock". Anyone care to comment on the significance of that?

At the end of the day you've encouraged me to have a go at off-hand drill sharpening myself. While creating a new point on a really knackered drill is still a distant goal, I've found it fairly easy to touch up the edges of a just-past-it example. So thanks for that, everyone.

Alan

Snip

Your link

a further link to "drill point geometry" This article is in my mind well worth a read and may have been missed by some not interested in the drill grinding fixture.

Richard