Re: Leadscrews, PCB router experiment

Hi,
I just tested the 60 degree mechanical etching bits from
Think and Tinker. They are micro grain carbide, and they stick
to a magnet. T&T told me to use 30,000 RPM at 16" per minute
when milling. I am running the bits at about 8,000 RPM with
a feedrate of 5" per minute. My boards take around an hour to
cut at that rate. For wider isolation paths a carbide drill bit
is a cheaper option. I do IC boards. This is Kleinbauer's
method. He also told me to coat the board with motor oil before
milling. I find this keeps the dust down.

Bob

--- In CAD_CAM_EDM_DRO@y..., Jon Elson <elson@p...> wrote:
> JanRwl@A... wrote:
>
> > In a message dated 24-Jul-01 02:21:40 Central Daylight Time,
> > elson@p... writes:
> >
> > > The experts can tap the shank on their fingernail and listen
for the ringing
> > > of the cantilevered drill bit. If it rings with a very high
pitch, close to
> > > 10 KHz, then it is carbide for sure. HSS is magnetic, of
course, but some
> > > other cutter steels are not.
> > >
> >
> > The most OBVIOUS way to tell "in an instant" is to "weigh" the
piece in your
> > delicate fingers! If it is OBVIOUSLY heavier than steel --- like
LEAD would
> > be, only even heavier, yet! --- it is solid-carbide! Dull grey,
not shiny,
> > like HSS.
>
> Unfortunately, the drill bits in question are quite small, and the
shanks are
> often HSS or similar material, so the tiny drill bit's weight is
lost in all
> that.
>
> > Carbide is even MORE magnetic than HSS!!! NOT a useful test!
>
> I find this hard to believe. At least, PURE WC (Tungsten Carbide)
is not
> magnetic at all. The various commercial formulations often have
large
> amounts of Cobalt and other magnetic metals alloyed in them, which
makes
> them mildly magnetic. I just went into my shop to check this, and
found
> most of my "solid carbide" tools to be very slightly magnetic,
although the
> shanks of many of them were much more strongly magnetic than the
> cutting end. I didn't fina any where the cutting end was strongly
magnetic
> at all, but the HSS tools definitely were.
>
> Jon