Re: Machining

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: Ian Macky <ian.macky-at-oracle-dot-com> 

 > Gerry:  high speed steel drills are cheep and easy to sharpen. Carbide are
 > the best most expensive and hard to sharpen. Cobalt are in-between. The
 > coated cut well and can not be sharpened so your investment is lost as a
 > throw - away item.

My $0.01 is that High Speed Steel (HSS; not to be confused with the other
HSS, High Strength Steel, which is the sheet metal used to form unibody
cars) stands overheating pretty well, which is one reason it's popular
with hobbyists, as they tend to be a little more abusive of tools (mostly
through lack of training/education).  But if you scorch the cutting end,
you can grind it off, removing all the Heat Affected Zone, and re-form with
Drill Dr. or similar.  So, HSS bits can have a long life: they get shorter
and shorter, but still Drill On.  Cost effective.

--ian