Sharpening drills with a tool grinder

I use one in my end mill sharpener but it's a cup with a ring of grit attached to it, basically the same construction as with most diamond wheels.

Mount them onto a mini lathe carcass.

So do you grind a flat, angled relief that way? Or do you rotate the bit somehow and generate a curved relief?

I think the relief has to be flat, and narrowed by hand-grinding the back relief. End mills drill well enough with a narrow flat relief. I rough out slots by plunging to avoid dulling the edge flutes which are harder for me to resharpen.

I suspect they will be good enough for controlled machine drilling but might dig in excessively freehand.

jsw

Types of drill bit relief have actually been studied, but I haven't looked at that stuff for around 30 years. Somewhere I even wrote an article about points and reliefs for production drilling, and it was a pretty long one.

I'm beginning to hate getting old. d8-)

I apologize for starting a string of misused terms.. I should've used land (or flank) instead of "flute" in my posts (flute is where there is no metal).

Anyway.. what you're describing here is the 4-facet grinding technique.. which I mentioned in my first reply. Drill points don't absolutely need to be ground with conical relief angles, and for many purposes, different grinds are more effective.

The use of carbide seems to be becoming excessive, as if it should be acceptable as the best cutting tool material for any purpose.. it's not. HSS cutting tools are the most cost effective for most home shop uses and small shop operations. Learning to sharpen HSS cutting tools apparently seems to be too challenging for some folks that don't realize that it's not difficult. If they can't have a "drill-doctor" solution for resharpening cutting tools, many folks seem to think carbide will be the ultimate solution.

When the misguided carbide user is faced with throwing away or resharpening expensive cutting tools, then they realize that resharpening can be even more expensive than HSS.. so instead of being the ultimate solution, carbide often becomes the beginning of a new set of problems.

I think that many, if not most, small shops would agree with you. Carbide inserts are one thing. But solid carbide is something that doesn't often make sense in a home shop. Even small job shops usually send solid cutters out to the specialty cutter-grinding shops.

I'm not a fan of offhand grinding of HSS drill bits, but it can be done by almost anyone with a little practice. If you don't mind oversize holes, they work fine in most jobs.

Grinding carbide is much more of an ordeal, whether you struggle through with silicon carbide or you spend money on diamond. You really need to have all the angles right.

If you are going to hand grind drill bits you should get one of these or something similar to get the angle and drill tips even. There are cheaper ones available.

John

Yeah, they're handy, and I've used one. I just use my little General fixture now, and it's not bad. I wanted to make a Quorn at one time but I could never get that much time together when I had my milling machine.

I have a Sellers drill grinder for the larger drills and it works fine. The small ones under a quarter inch aren't worth screwing with unless it's the last one in the draw. I just got about of ton of larger drills up to three inch dia. that I have to sort out and inventory. I got the shelves up but that is about as far as I got. At least most of the drills are marked for size with a white paint marking pen.

John

As I say, I use it to rough out broken bits before I finish them on the Drill Doctor. Saves a lot of wear on the DD's wheel. Gerry :-)} London, Canada

This sounds very much like what is commonly called a "split point".

How big are your carbide drills? Most that I have are tiny things for printed circuit work -- and those which I have examined with magnification are certainly split points.

Enjoy, DoN.

Those ar 1/2" diameter.

I have only 6-7 or so of carbide drills, and many times that number of HSS drills. This answers Wild Bill's point. I am not some kind of a carbide freak when it comes to drilling. It is the opposite. I want to sharpen the carbide drills, mostly because a) they are expensive and b) they are easy to grind, having only two flat surfaces per flute.

O.K. Big enough to let you get good measurements on the angles of the flats.

Well ... "easy to grind" -- in shape, perhaps. However, without diamond grinding wheels, it is difficult to do on a normal grindstone. even the green ones don't do that good a job on carbide.

But yes -- they are worth while resharpening assuming you have things for which they are a benefit. Your drill press is likely not fast enough to benefit from the carbide -- but if you are drilling things which are abrasive -- to include things like glass-epoxy printed circuit boards -- yes the carbide bits are a real win.

As an example, back when I was making printed circuit boards (before it was cheaper to send off files to a company and have them make them, complete with plated-through holes), a single-sided G-10 board with about four 16-pin DIP layouts and a few resistors and caps would burn a #70 HSS drill bit in a sensitive drill press to a needle shape (leaving furry holes through the board. But a solid carbide #70 bit could go through many such boards -- with the most common failure mode being a slight twitch in the board while the bit was in it. Solid carbide bits certainly do *not* like side forces. ("Plink!" -- end of bit. )

The real trick in doing spilt points is getting the back grinds to meet in just the right place in the center of the bit. If you can set up a tool to do this for you -- you are well ahead of the game.

Good Luck, DoN.

Reminds me of the time my boss grabbed one of my carbide PC bits and said 'lemmee show ya how to sharpen these'.

"Whoa, gee I dunno, Al..." PLINK!

The expression on his face was worth it. :)

--Winston

I used to be much better at grinding drill points freehand when my vision was better.. down to about 3/16".. and split-points weren't difficult to attain after examining some real industrial drills.

Drilling in general isn't very accurate, but it's still the most effective cutting tool for fast metal removal, which is why maintaining sharp drills is of importance to the HSM. Many drill users are still worried about destroying drills with heat when resharpening, which can impede their concentration.

I presently have a TDR-SRD model 80M and a couple of other fixtures, and they can all be a bit fiddly when trying to go thru a batch of different sizes or lengths.

Carbide tipped circular saw teeth are great (and inexpensive), but they are at least sharp when new.. and provide a very good service life in wood. A lot of carbide metal cutting edges don't even have a well-defined edge, and my lightweight machines generally don't perform well with typical carbide tooling.. although surface finishes equivalent to a cactus aren't a problem. Those surfaces give the Loctite something to grab onto.

And what kind of stone was he trying to do it on -- the usual gray stone which comes with most bench grinders? Even a green one?

Yes -- a tiny solid carbide bit really needs to be held in a fixture instead of hand held. Just too much chance of breaking it.

Enjoy, DoN.

Generic gray stone. Works fine for turning broken PCB bits into scriber tips.

Oh Yeah. Al found that out, for sure.

--Winston