Thread: Sharpening Countersink Bits

Originally Posted by Ben Dono

Off topic though... I have been told the countersinks with a single hole in them are primarily for deburing holes... Is that right? I could not justify spending the $60 to find out!..

They are available in sets of different flavours, at home I have a 60deg taper set that are for deburing, and a 90deg taper set for countersinking. Have used the 90deg style for both deburing and countersinking for 12 years in a variety of materials from timber, MDF, through to aliminium, mild and stainless steel bar and tube for holes from 1.5mm to 19mm diameter. A hell of a lot of this was with visible metal furniture components either for chrome plating (steel) or mirror polishing. Surprisingly, the mirror polished stuff is drilled and countersunk after polishing, as polishing last tends to make the rim of the countersink elliptical.

In our trade experience, through holes are the only countersink for metal that will not chatter in the hole and leave an uneven surface and finish.

The kind I am talking about - the only one I have - fits that diagram supplied earlier in the thread.

It is a cylinder machined to a point at one end and with a shaft machined at the other end to fit in the drill chuck.

Then there's a section cutaway from the tip of the point straight down along the long axis of the thing.

Doing that gives you a cutting edge at one side of the cutaway, along the incline leading to the tip, and a trailing edge at the other side.

Only way to sharpen that cutting edge is to take material off all around the cone.

Given that earlier post saying the cone is elliptical rather than perfectly circular then not so much material has to come off, maybe, because, of course, the elliptical shape gives some clearance behind the cutting edge.

But it's probably so little that its practically necessary to remove material all around.

I can't see that it's a big deal. Not in my 'shop' (backyard, that is). Because the work it has to do I could virtually do with my thumbnail if you'll forgive a little exaggeration for effect.

Take a little edge off some softwood, or Mdf? At 2000 rpm or whatever it is? You could cut grooves longtitudinally down the cone and make a tapered reamer type thing out of it and it'd cut those edges away - 'countersinking' the hole.

Virtually the only way to stop the thing working is to do what I did the first time or two that I tried to sharpen it. Trust me.

I tried to make a slightly acute angle on the cutting edge by filing (whetstoneing, really) the edge.

What I was doing was lowering the cutting edge below the circumference of the spinning disk of the thing.

My new sharpened cutting edge never touched the wood.

I'd made it blunter than it ever was.

Like I just said I reckon if I'd just made a cut longtitudinally down the cone from tip to base - just one cut only, even - that would have become a new cutting edge and it would have started cutting.

When i get another one I'll play with it and see.

'Fluted'. That's the word. 'Fluted'. If I cut flutes into the cone it'd cut away and countersink I'm thinking.

Are those things a modern design? Or is that a traditional design from the days of brace and bit?

Thanks Malb! That's a good bit of info. I will keep in it mind!

Abrogard, I think most of us were on the same page with your first description.

I'm guessing but think it would be easy to loose your way with these countersink bits once you start changing to many angles. It's not like a twist drill where you can just grind it off and start again.

I can see kryn's point in that regard, however I bet you still can freehand or jig sharpen this cutters both on the inside cutting face as well as outside cone. Someone will eventually put up a good video tutorial on it!
Free hand grinding the outside worked for Elan an I have done it as well with decent results.

Probably the easier approach to it though is just touching up the cutting face.
Most people treat cutting tools as disposable items now days. It's a shame really but a blessing for the backyard sharpeners. I can see that the vast majority of users would toss a dull countersink or just force it through the cut.

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.

I'm ALWAYS grumpy lately.
The countersink with the hole in it, is all I ever use, as the majority of my work is steel, occasionally used on wood. I do have a set of drill bits with a countersink on them for pilot holes for screwing.
Kryn