I have purchased (thru Ebay) sets of 50 assorted sizes for <$20 US. There=
's
a guy that sells these regularly  - put in a nice plastic case with holes=
 in
the base to hold all the drills neatly. My only gripe with him is that he
doesn't mix the sizes fairly - often there are too many of an unwanted si=
ze
and only one or two of the sizes I want.

BTW, these are excellent for metal work. I have used them on various meta=
ls
down to about .007 in. and can often get 100's of holes from one drill. J=
ust
be sure to use coolant, spindle speed and feed rates according to standar=
d
practice for the material being drilled. I'm sure that in these sizes the
spindle should be   thousands of RPM .......Hmmm, lets see, in inches it
goes something like this:

RPM =3D cutting speed * 12 / diameter X pi
so .25mm in steel =3D  100 x 12 / .010 * 3.14 (close enough) =3D 38k RPM.=
 at a
minimum cutting speed of 40, it comes down to about 15kRPM.

Cutting speed is in SFPM, or Surface Feet per Minute. For aluminum use
between 200 & 300 SFPM, for steels, use from 40 to 150, depending upon th=
e
carbon content of the alloy. (don't even try to drill aluminum dry with
carbides)

A tight spindle, well-held workpiece and gentle feed rate of perhaps < .0=
01
in/rev will have you making nice small holes in metals with these drills.
That .25 mm hole in 1/8 in steel should only take about .5 sec of feed to
get through. If feeding by hand, a good rule of thumb is that if you can
feel resistance against your feed, the drill has probably just broken - y=
ou
really need a sensitive, light touch. Mini-drill presses for this kind of
work are often referred to as "sensitive feed" type.

C


> -----Original Message-----
> From: pic microcontroller discussion list
> [mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Jan-erik S=F6derholm (QAC)
> Sent: Sunday, April 13, 2003 6:55 AM
> To: PICLIST@MITVMA.MIT.EDU
> Subject: Re: [EE]: *Thin* drill bits
>
>
> Sure !
> Since yesterday I'v been thinking about this.
> What about a "thin-drill" box of 50 mixed
> sizes 0.25mm - 0.55mm ? What would you be
> prepared to pay for that ? $10 (+p&p)
>
> Or what did you ment by "make a set available" ?
> To give them away for free ? Well, I'm not *that*
> desperate right now :-)
>
> I'v also been thinking about making the same kind of
> "large-drill" set available with lets say, 25 drills
> between 2mm and 5mm.
>
> Anyway, our guest room is full of drill boxes right
> now (about 35.000 drills total) and my wife is a bit
> "disturbed", so I'll better take care of them (the drills)...
>
> Jan-Erik.
>
> Larry Reynolds wrote:
>
> > Jan,
> > Maybe you  could make a set (like 10 each) available to all on the
> > list.  I'd be interested in a set.
> >
> > Larry
>
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