Thread: Sharpening Countersink Bits

Sorry, but I think that using a grinder is a little like frying eggs with dynamite.
You won't get quite the result that you think you will.
First, the steel of the countersink is hard enough to take very little to tune it up.
Wipe the cutting edges with a black felt marker so that you can see where the metal is coming off. Now, 600 grit or 800 grit W&D paper on a hard paddle.
Do 1500 if you can get it.
I suspect (without knowing) that you have made some serious wire edges on the flutes. They will seem dull. You need to wipe the back sides of the flutes with a riffler file to ease those away.
For the price, I'd buy another to work with and fool with the wreck to figure out how to do it right the next time.

"I'd buy another to work with and fool with the wreck to figure out how to do it right the next time"

That's probably right.

Thanks

I would be treating it the same way you do router bits...... Funny that.... I just worked out that's what RV was recommending! A little wet and dry glued to a paddle pop stick to touch up the face.

Yeah. Do the flute(s).

I'm not a fan of W&D. Get some decent abrasive sheet like 3M micro-finishing or lapping film. Lasts much longer. The Sandpaper Man

Or try a diamond hone. Diamond Mini-Hone Sharpeners | DMT® - Diamond Machining Technology

I presume you mean a cross section like this?
Countersink.jpg
If so removing any metal at the edges marked with the black arrows will render the bit even less effective.
The chances are the reason the countersink is not cutting is because a small amount of metal has been worn away from the outer and the right angle corner needs to be re-established.

If you want to touch up the outside edge you must remove an equivalent amount of metal all the way around the bit.
This is quite hard to do without rolling over the two edges marked with the black arrows.

This means that only the edges marked with the red arrow should be touched. As already described there are several ways to do this. If the edges are rounded then most methods will be too slow and I have even used a dremel with a grinding wheel to apply light strokes to that face and then I use a diamond lap to finish up.

I just tried this.

Found it quite easy really.

My bit was screwed up from earlier attempts to sharpen where I hadn't removed metal all around the cylinder I'd just tried to touch up the edge. Didn't work because the cylinder remains the same diameter of course.

But this thing is only taking a bit of edge wood off a screw hole. For me that's usually softwood or mdf and I commonly use 8 and 10 gauge metric screws.

So I took to it with a sharpening stone and just went all around as best I could. Feeling the edge with my finger for sharpness. Using the bottom edge as a bit of a guide.

Worked fine. The thing's better than it has ever been.

Just thought I'd mention it. When I'm following guides like this it makes a difference to me to know whether I'm attempting something that should be hard or should be easy, something that's critical or not...

I was thinking about this a few weeks ago, and I dreamt up a technique that I want to try:

1. bore a full depth CS into some pretty hard wood, and make 3-4 of these holes.
2. put some diamond paste of different grits into the holes
3. Run the CS bit in reverse in the hole
4. wipe clean, and proceed to next finer grit hole.

I might 'speriment with it later on and see how it goes.

sounds good to me....

i can't quite understand how they're supposed to work with the constant diameter all around - where's the 'attack' for the cutting edge?

I suppose somehow it comes just from the large gap between cutting edge and trailing edge?

It took a while to learn, but the trick is to sharpen via the through hole and leave the cone alone. That creates a fresh edge at the junction without changing the relief angles etc.
Abrogard, the 'cone' section is not truly circular, (slightly elliptical) and the through hole is centred on the widest point of the ellipse. This arrangement means that the cutting face at the junction is slightly proud of the junction face on the opposite side of the through hole, regulating the cut for each revolution. The elliptical grind is obvious on the larger sized countersinks, but virtually impossible to see on the smaller units.
Any attempt to sharpen the cone reduces the amount that the cutting edge protrudes, and reduces the tool to scrap.

I sharpen the cone all the way round on a bench grinder using the side of the wheel instead of the face (have to go all the way around to ensure enough of a relief angle). Works a treat.

Sharpening anyway but through the hole will reduce the CS bit to useless scrap as has been suggested before, Google show a couple of pics where one is sharpened on a tool and cutter grinder, but a majority of us don't have one. When I bought mine this is what was on the packaging "The recommended way is to use a Dremel type tool with a fine stone and take a couple of thou approx off the leading edge, it doesn't take much to put on a new edge." A round diamond file would do the same thing.

Kryn

Originally Posted by KBs PensNmore

Sharpening anyway but through the hole will reduce the CS bit to useless scrap as has been suggested before

Not true, just takes practice to get it right

Bit grumpy tonight Kryn?c

I think this thread started with a different style of countersink bit than your describing. ( forums are cryptic at the best of time...for me anyway!) I can't say I have ever used a countersink with the hole in it but I have used most of the others. I think these guys are talking about the countersink bits with one cutaway.

In the past I have usually only touched up the inside face of these but I could imagine you can grind the outside cone. We are lucky as their are a lot of great youtube videos on hand grinding normal twist drills. They look complicated until you stumble across a few good videos that prove you can do it with a bit of practice. It's not that difficult once you shown a few pointers. I'm sure their are a few oldies out there that know how to hand grind these countersink bits!

Originally Posted by Ben Dono

Bit grumpy tonight Kryn?c

I think this thread started with a different style of countersink bit than your describing. ( forums are cryptic at the best of time...for me anyway!) I can't say I have ever used a countersink with the hole in it but I have used most of the others. I think these guys are talking about the countersink bits with one cutaway.

That's the one I'm talking about, might have misinterpreted the OP though...