sharpening HSS drill bits

[disco_monkey79]

Hello,

I've got a set of titanium-coated HSS drill bits. I bought them from Halfords a few years ago, and they've been great.

However, they're now pretty much all blunt (they're OK for wood, but steel now thumbs its nose at 'em). I've never re-sharpened drill bits before - is this practical/worthwhile with HSS, or should I just buy a new set?

If sharpening is possible, what techniques/equipment do people recommend?

Many thanks

 

[grandad211]

Bin them, if you've worn through the Tin coating, they're only pointy bits of metal now.

 

[Graham Orm]

Hello,

I've got a set of titanium-coated HSS drill bits. I bought them from Halfords a few years ago, and they've been great.

However, they're now pretty much all blunt (they're OK for wood, but steel now thumbs its nose at 'em). I've never re-sharpened drill bits before - is this practical/worthwhile with HSS, or should I just buy a new set?

If sharpening is possible, what techniques/equipment do people recommend?

Many thanks

It's easy enough if you've got a grinder, this just about cover's it http://www.youtube.com/watch?v=DGibYeprpkk You start with the cutting edge against the wheel and roll the drill so that all metal behind the cutting edge is lower than the cutting edge. The 118 degree isn't an absolutely critical angle, but it's easy enough to make a gauge with a protractor. What he doesn't mention is that it's important to keep the point central...don't grind more off one side than the other or it will cut larger holes than you are expecting.

Never tried to sharpen Titanium coated. Personally I throw away small drills and just replace, they are too fiddly to try and sharpen anyway.

 

[disco_monkey79]

Thanks all. I have a bench grinder so will have a go at one or two of the larger ones

 

[CHJ]

Preferably use a White Oxide wheel if you have one, better finer finish, should be no problem at all.

Forget the yellow Titanium Nitride coating, of no relevance as far as sharpening, basically there to harden the surface and reduce friction of waste removal, in most DIY applications I doubt many will detect any difference.

Freehand sharpening is a knack but once mastered is well worth the few minutes and a couple of scrap drills to play with.

Like any cutting tool the quality of results and ease of use is all down to keeping the edge sharp, you really need to to get in the habit of checking the sharpness before any new project, it's a matter of a few seconds to bring back the edge.

 

[Graham Orm]

PLUS!!! Important to keep it cool, dip into cold water after every grind.

 

[CHJ]

PLUS!!! Important to keep it cool, dip into cold water after every grind.

True for Carbon steel but not HSS.

As long as you keep the temperature down below any edge bluing then HSS will be fine, it can stand some 550oC (dull red colour) before loosing hardness. If you can hold a HSS drill in the hand then it should be fine.
Quenching a very hot HSS in water can cause micro fractures of the fine edge.

 

[Graham Orm]

PLUS!!! Important to keep it cool, dip into cold water after every grind.

True for Carbon steel but not HSS.

As long as you keep the temperature down below any edge bluing then HSS will be fine, it can stand some 550oC (dull red colour) before loosing hardness. If you can hold a HSS drill in the hand then it should be fine.
Quenching a very hot HSS in water can cause micro fractures of the fine edge.

Thanks Chas, good info that. Trouble is blueing happens so quick on something as small as a drill.

 

[CHJ]

..
Thanks Chas, good info that. Trouble is blueing happens so quick on something as small as a drill.

Yes it can but a good sharp grinding wheel* with little or no pressure applied is the answer.

The occasional straw or blue on a HSS will not be detrimental but it's a good indicator that sharpening routine or method could do with improvement.

* a grinding wheel needs to be kept unglazed and sharp just the same as the cutting tools.