drill bit sharpening

Ahma haveta read it 15 times! Man, what a cupla pictures--or a video--wouldn't do!!

But, perhaps Teenut's bottom line is: Real men sharpen bits by hand.... :)

---------------------------- Mr. P.V.'d formerly Droll Troll "Karl Townsend" wrote in message news:CAbce.855$ snipped-for-privacy@newsread2.news.pas.earthlink.net...

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Proctologically Violated©®
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Lots of good advice has been given on how to freehand sharpen drill bit and plenty of people are well skilled in this art. Pretty well all of it is directed towards duplicating the usual offset cone geometry found on standard machine ground jobber drills. However, for newcomers it is sometimes easier to learn to use use the 4 facet drill grind.

Commercially this is only used on the more expensive special purpose drills because it needs 2 extra grinds per drill point and is only marginally better.However the beauty of the 4 facet system is that it's much easier to describe and understand.

It's best carried out using a cup wheel.

For resharpening a blunt but OK drill, present one drill cutting edge to the wheel.

Set the length of the edge horizontal and almost touching the wheel surface

Tilt the top surface of the flute which forms the cutting edge roughly 10 deg.

This is exactly the same operation as grinding a 10 deg front or side clearance on a lathe tool but now only grind away as little as possible - just deep enough to remove the blunt area.

Repeat the operation for the second drill flute taking care to grind away the same amount so that the facets are symmetrical. If you get this a bit wrong the drill will still cut well but will drill oversize.

This completes the sharpening of the cutting edges but the back edge of the flutes may foul the newly cut surfaces. You need an additional grind to eliminate this.

The exact shape of this grind is not important because it doesn't need to form part of the cutting action.The easiest method is simply an exact repeat of the first sharpening operation but using 30 deg downward tilt. In an ideal world this grinding should continue until the new facet overlaps the first facet halfway along the central chisel edge. However this is not essential and, as long as the new facet extends 1/3 or more round the periphery of the flute, clearance will be established and the drill will cut just fine.

If you haven't got a cup wheel you can grind on the periphery of a disk wheel but it's a bit more difficult to eyball the angles.

If the drill is damaged or mis shapen, use the 30/60/90deg protracter from a childs geometry set. With the long hypotenuse edge laid along the drill the shorter remaining edge shows the correct angle to present to the wheel.

Jim

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pentagrid

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Waynemak

My M5 does wierd with parabolic flute drills. But other than that..works fine.

Gunner

Liberals - Cosmopolitan critics, men who are the friends of every country save their own. Benjamin Disraeli

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Gunner

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