Tool Sharpening

In order to best visualize the relationship of the various angles of surfaces and
 how they relate to real cutting tools, just examine the photos with matching
 numbers. These are 1/4" square HSS lathe bits ground to three different cutting
 profiles.

 I like to grind my bits on a 60-grit gray aluminum oxide wheel for all the initial
 rough grinds. You do not need to waste time on a fine wheel that barely takes off
 metal. Finished surfaces are ground on a white aluminum oxide 100 grit wheel.
 This finer wheel puts on such a good finish that you almost do not need to hone
 your edges. As you machine, you might have to touch up the various edges
 avery once in a while. Many times you simply can get away with a light honing
 with a fine stone and some oil. Heavy nicks and other defects will require a pass
 through the 100-grit wheel. 

Angles of the clearances will vary from almost zero if you are going to machine
 brass, to 10 -20 degrees. These angles do not need to be exact. Just get it close
 and it will work just fine. Certain materials like aluminum will need much steeper
 clearances or they will not machine cleanly. I like to put around 20 degrees of
 clearance or "rake" on all my bits that will be cutting aluminum. Steels and other
 ferrous metals will do well on angles between 10 and 15 degrees. You will have
 to experiment to see what works best.

 Those of you who scrounge in metal scrap yards will no doubt find plenty of good
 and cheap material to work with. The problem is that many times you may not be
 able to accurately identify the particular alloy you bring home. Aluminum and
 stainless steels may be of unknown parentage and will display different
 machining characteristics. You will have to experiment to see what works best.

Though the diagrams above depict the cutting point as a very sharp one, you
 should always hone a very slight radius to break the sharp point to a gentler one.
 This will result in much smoother finishes all of your cuts.

 Do not ever grind with such pressure and for such lengths of time that you see
 the metal turn blue. This is the quickest way to ruin a bit. Keep a bucket filled with
 cold water and quench that tool frequently. How often you ask? My rule of thumb
 is if you are holding the tool about an inch from the end you are grinding, and it
 begins to burn you, you need to quench!!!