Subject: Re: Drill Sharpening

From: [email-masked] (David Jenkins)
Date: 16 Dec 1994 10:16:37 GMT

>From  article <[email-masked]>, by Doug MacDonald <[email-masked]>:
> [email-masked] (Frank Carlsen) wrote:
>>
>> 
>> While trying to remove an ugly chip from the tip of one of my carbide 
>> lathe tools tonight, I held it to the wheel a little too long and caused 
>> a slight burn. Given my impatience this does happen all too often, but I 
>> haven't found that it causes any problem with the tool. But I wonder, 
>> does this slight burning cause any harm to the underlying steel? 
> 
> Yes--you take the temper out of the steel, and the drill won't stay
> sharp as long.  A temperature high enough to cause a discoloration
> of the steel (typically blue or purple) softens the steel.  As far
> as i know, though, it doesn't damage the steel in any other way.
> 

Hold on... I'm confused... the original message talked about a _carbide_
tipped tool which was overheated, not a HSS one.

If the steel backing for the carbide tip got overheated then I can't imagine
that it'd make a great deal of difference.  Other possible problems may
arise though, e.g.

1. The brazing between the tip and the body may be overheated or weakened -
this is unlikely as industrial carbide tips are run red-hot, with coolant
flooding over it.  This might be a possibility if the tool isn't top-quality
industrial grade.

2. The tip may suffer microscopic cracks, leading to an early failure.

On the other hand, you may not notice any difference.  :-)

-- 
David Jenkins						Not long now...
--------------------------%<-------------------------------------------
	 Cuius testiculos habes, habeas cardia et cerebellum.
			Terry Pratchett --- Small Gods.