Re: Machining

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

Original poster: Jim Lux <jimlux-at-earthlink-dot-net> 

At 12:18 PM 4/21/2004 -0600, you wrote:
>Original poster: Terry Fritz <teslalist-at-twfpowerelectronics-dot-com>
>
>Hi Gerry,
>
>High speed steel is a relatively cheap hard tool steel used for most 
>ordinary purposes.  It cuts wood plastic and other easy materials 
>well.  The bits can bend so they are very durable for say hand 
>drills.  The steel is tempered so if they overheat they are softened and 
>ruined.

If the bit discolors (from what it was when it was new), you've probably 
lost the heat treatment.

Steel drill bits are also easily sharpened.  Get one of those nifty jigs 
(or something like a "drill doctor"). Watch the overheating while sharpening.

HSS and a decent lube will work very well on lots of materials (including 
iron and steel, because the tool is harder than the work), except ones that 
are hard.. see below.



>Tungsten Carbide is a very hard material and can cut hard materials like 
>glass, rock, stainless steel...  It is pretty heat resistant and will not 
>de-temper.  Difficult to sharpen and it is usually braised to a steel 
>backing.  It weakness is that it is very brittle and can crack easily.  It 
>is often used in wood working tools where cracking is not a big problem 
>with the soft wood.

Circular saw blades with carbide tips are common, but watch out, sometimes 
you'll lose a tip.  The blade will still cut fairly well, but will be 
unbalanced.


>   Very expensive compared to steel.  In our case, carbide tools stand up 
> to FR-4 phenolics very well where tool steel dulls fast.

Because FR-4 has glass in it. Glass is very hard, compared to the usual 
tool steel, so cutting glass fibers dulls a blade real fast.


>  Almost all printed circuit board drilling and routing is done with very 
> high speed tungsten carbide tools.  Carbide is often used in metal 
> working lathes where a small tool edge can last a long time in a well 
> controlled situation without being subject to impact damage.