Sharpening a snail countersink brace bit.

[baldpate]

Hi,

does anyone know how can I sharpen a snail-type countersink brace bit, please? Is there a standard method?

I've already got a small size one which is sharp, and cuts very nicely, so I know that the larger one I later bought is blunt. I've tried rubbing the inside of the cutting edge along the side of an oil-stone, without any discernible improvement. I'm assuming one doesn't attempt to grind the outer cone. Any tips, or tricks (before it gets binned)?

Thanks

Chris

 

[AndyT]

There's a funny thing. I too have nice sharp snail countersink that I use in a brace. And last weekend I bought another one, for pennies, which is blunt!

I will try and get round to sharpening it sooner rather than later and take some photos.


First thoughts are to use a round needle file, or the edge of a small slipstone, on the inside of the curl, leaving the outside untouched, as you say.

 

[Phil Pascoe]

I have a snail countersink for a No.131 Yankee screwdriver. I managed to sharpen it on a diamond plate and it will do a counterbored countersink in one hit.

 

[Cottonwood]

I have often wondered about this...
Funnily enough only yesterday I was studying how plane floats can be made, where the teeth are file seperately, where they use a blue stain to show how far to file down.
Perhaps the countersink needs to becarefully rotated along the side of a grinding wheel (to get a perfect cone) then stain it, then file until the blue has all gone off each tip? So as to get each of the 8 (?) teeth all on the same plane so to speak, just a thought
cheers J R

 

[AndyT]

I got round to trying this tonight.

In case anyone else wants to try - or knows what they are doing! - this is what I did.

This is a known good countersink, of the sort I call a snail - but we could be at cross purposes - there is another sort which looks like a cone with a hole through it, as well as the commoner 'umbrella' type.

This is the knackered old one, possibly not worth the 20p I paid for it:

I tried a gentle approach with needle file or slipstone but was getting nowhere. A conical stone in a Dremel-alike was more use:

I was trying to undercut a bit, to leave a sharp scraping edge. This sort of worked. I followed up by grinding the whole of the outside of the cone thouugh, trying to regain a bit of relief angle. If there is any part of the cone sticking out further than the edge, then the edge will be held off the wood and not cut. So I was trying to make it 'all downhill' from the edge. (This does make the cone a bit smaller, but not too much.)

After the grinder I smoothed off the outside surface with a little diamond hone.

Here is the proof that it did work; whether it was worth the effort is another question!

 

[Cottonwood]

We were at cross purposes, I had in my minds eye the sort I own with 8 seperate cutting edges (umbrella shape?) I have another that is a perfect cone with just one cutting edge. The snail ones seem exotic!
Thinking about it, it should be possible to simply file 8 new edges on an "umbrella" type with a 3 square file, its just the "topping" phase (as in saw filing) that would be tricky... :?: any ideas

 

[Phil Pascoe]

IIRC that's a "rose" countersink. One cutting edge is usually a "snail".

 

[baldpate]

Thanks for the post & pics. Andy. Mine looks much like the dud in your 'before 'picture, with the curl needing quite a bit of under-cutting to restore an edge. Like you, I made no progress with files & honing stones. I didn't think of using a dremel-type tool - that certainly looks like the way to go.