HSS Zero Flute Countersink

[rxh]

After countersinking about 50 holes in mild steel this bit no longer cuts. Please can anyone tell me how I can re-sharpen it?

 

[Rorschach]

They are not terribly easy to do but you can normally get one or two "honings" out of them before the edge geometry is gone.

Use a round slipstone or diamond file and sharpen the leading edge INSIDE the hole. If you try and sharpen the outside you will ruin the geometry unless you have a special purpose setup on a T&C grinder.

 

[TheTiddles]

Emery paper on a stick, but I think that type of countersink is not meant for metals?
Aidan

 

[chaoticbob]

They work fine for countersinking metal - I often use them in mild steel.
Like Rorschach, I sharpen inside the hole - there's a good video explaining why and how here.

Rob

 

[Rorschach]

Yep they are designed to be used with metal (as well as any other material). I much prefer them over other styles of countersink as they are less fussy about speed, run a standard countersink too fast or get it off centre and you get chatter. Once that chatter starts the countersink never looks good, it always has that "starburst" look to it. The zero flute never chatters no matter how rough you are with it.

 

[rxh]

Thanks for your replies. I used the method of sharpening using a Dremel tool, as shown in the video linked by chaoticbob and I'm pleased to say that it worked fine